Despite its great successes for the standard rovibrational problem, there is still a large domain in which high-resolution molecular spectroscopy lacks both extensive experimental data and a complete and convincing theory: the full rovibronic problem. This is the case of a molecule in a degenerate electronic state, i.e. when the Born-Oppenheimer approximation breaks down. It means that the electronic, vibrational and rotational degrees of freedom must be treated simultaneously. Complex (ro)vibronic couplings (Jahn-Teller “effect”, etc) are then involved. Some octahedral transition metal hexafluorides and hexacarbonyls are known since many years to be stable open-shell systems with degenerate electronic ground states leading to very unusual absorption spectra. However, the extreme complexity of this kind of problem (from both experimental and theoretical sides) prevented to go any further in this direction until very recently. In this paper, we will give an overview of the tensorial rovibronic model that we have developed in the Dijon group for such systems. This model enables the systematic development of the rovibronic Hamiltonian and transition moments (dipole moment and polarizability) in a given degenerate electronic state. We will then review the current status of rovibronic spectroscopy of octahedral molecules. This includes the recent data obtained using supersonic expansion jet infrared spectroscopy V(CO)₆ and ReF₆, for which we will present detailed analyses.

Intramolecular vibrational redistribution in a polyatomic molecule leads to very considerable narrowing of spectra of purely rotational transitions in microcanonical ensembles of many vibrational states. It is discussed how this effect may be explored to study two important characteristics of intramolecular vibrational dynamics: the onset of transition form the regular vibrational motion to the chaotic one, and the rate of intramolecular redistribution of vibrational energy from one mode of a molecule to another modes.

The quality of the models used for the calculation of energy levels and line intensities is discussed for planar C_s type molecules in the case of strong resonances affecting the energy levels of at least two resonating states. The Hamiltonian model which is used classically to reproduce the energy levels involves for the v-diagonal blocks, rotational operators written in an orthorhombic reduced form as proposed by Watson [“Aspects of quartic and sextic centrifugal effects on rotational energy levels” J.K.G.Watson, Chap. 1, in “Vibrational spectra and structure”, J.Durig editor, Elsevier, (1977)]. This means that the non-orthorhombic character of the molecule is only accounted for through the operators off-diagonal in v. For example, for planar C_s type molecules the resonances which perturb the resonating levels are taken into account in these off-diagonal blocks either by both anharmonic and C-type Coriolis operators for vibrational states of the same symmetry species in C_s (A’ ↔ A’ or A” ↔ A>>) or by both A- and B-type Coriolis operators for resonating states with differing symmetries (A’ ↔ A”). For a well-identified scheme of resonances this “classical” model gives excellent results when the perturbations involving the perturbed energy levels are rather localized. On the other hand in case of overall strong resonances this “classical” model may fail and it is necessary to use a Hamiltonian which possesses also non-orthorhombic terms in the v-diagonal part of the Hamiltonian. This is because a common system of inertial axes cannot be used for the strongly resonating vibrational states. This effect has also to be accounted for during the calculation of line intensities.

Experiments combining intracavity laser absorption and stepping-mode time-resolved Fourier transform spectroscopies are presented and discussed. They allow to record broadband absorption spectra comprised of hundreds of time-components for absorption path lengths up to tens of kilometers in the near infrared.

Modern quantum chemistry is the quantum theory of structure an dynamics of molecular systems. The development of quantum chemistry for almost 8 decades gave birth to many concepts of modern chemistry and created many calculation technique which are widely used to obtain preliminary as well as high-precision information on molecular properties. In the end of XXth century it becomes the real fundamental base of chemistry and the active tool for the qualitative interpretation of structural features and physical and chemical properties including dynamics of chemical transformations. It turns out to be a very power means to obtaining quantitative results for molecular clusters as well as isolated molecules in free states and in external fields. The computational programs created in the last decades of the XXth century and permanently refined provide the reliable quantitative information on molecular equilibrium configurations, harmonic vibrational frequencies and anharmonic force constants, frequencies and intensities of the first electronic transitions, energies of the formations and potential barriers, the parameters important for interpretation of ESR and NMR spectra, electric and magnetic moments, and many other characteristics of molecular systems. The last two decades turned many quantum chemists to comparatively large molecules especially those with the distinctly pronounced biological activity. Nevertheless, small molecules the calculation results for which can pretend on the highest precision still serve as a strong attractor for the people who deal with methodological as well as applied problems.

The review of modern methods of precision measurements of spectral line parameters used in Microwave Molecular Spectroscopy Laboratory in Nizhny Novgorod is presented. Various line shape models used for measurements of spectral line parameters are considered. Analysis of possible sources of systematic errors in parameters determination is given. Wide-range spectral studies possibilities and high accuracy of obtained parameters are demonstrated on example of investigations of practically important for atmosphere remote sensing spectral lines of water and oxygen by means of two spectrometers with complementary abilities.

High resolution FT absorption spectrum of H₂S from 5700 to 6600 cm^-1 was experimentally recorded and theoretically treated. As a result of the spectrum assignment 1100 precise energy levels were derived for the 2nd hexad interacting states of H₂³²S, H₂³³S, and H₂³⁴S isotope species including the highly excited (050) state. These energy levels were modeled using Watson-type rotational Hamiltonian and taking into account Coriolis, Darling-Dennison and weak Fermi-resonance interactions inside polyad of interacting states. An average accuracy of the energy levels fitting is of 0.0019 cm^-1 for the main isotope species. New evaluation of the band origin of the dark (012) state E_v = 6385.299cm^-1 is obtained from the fitting process which agrees well with recent prediction by Naumenko et al. (J. Mol. Spectrosc. 50, 100-110 (2001)). Precise line intensity measurements were performed for more than 1200 absorption lines with accuracy varying from 1 to 7%. These intensities were modeled within 3.3% using wavefunctions derived in the process of the energy levels fitting. The transformed transition moment expansion with 29 terms for 1088 intensities was used. Detailed and accurate H₂S absorption line list was generated in the HITRAN format for the analyzed spectral region.

New high-resolution experimental data are reported on the linestrengths and self-pressure-broadened Lorentzian widths for the P₁(1)-P₁(10), R₁(0)-R₁(15), and P₂(13)-R₂(12) vibration-rotation lines in the fundamental and the first overtone absorption bands of HI. An improved dipole moment expansion as a function of the reduced nuclear displacement is generated and compared with the available ab initio calculations. A new set of the Herman - Wallis coefficients is obtained, which is in a better agreement with theory than previously published results.

The analysis of interaction between the ground X¹A₁ and excited B¹A₁ electronic states of the water molecule have been made and it was shown that the centrifugal distortion near the linear HOH configuration may lead to a considerable state mixing in the case when both lower and upper state wave functions are localised near linear configuration. As a result, transitions to the high-bending states, such as (0V₂0) with V₂~20, within the ground electronic state may be intense due to intensity borrowing. This effect appears to explain the weak 0.27 mkm feature in the near UV water vapor spectrum observed early experimentally.

It is shown that torsional Coriolis coupling can alter the torsional splittings in molecules with hindered internal rotation. Splitting patterns that would occur in the absence of any vibrational contribution to the torsional angular momentum, with reference to a molecular axis system (IAM), are called regular. It is shown that different sets of vibrational coordinates, corresponding to vibrational states with different splitting patterns, can be defined for modes normal to the internal rotation axis. The forms of normal coordinates appropriate to basis vibrational states with regular and inverted splitting patterns are identified. It is found that in normal coordinates appropriate to vibrational states with regular torsional splitting patterns, the relative orientation of the displacements of pairs of atoms belonging to different molecular moieties is independent of the internal rotation angle, and relative displacements normal to the internal rotation axis can be cis or trans at any conformation. On the contrary, in normal coordinates appropriate to vibrational states with inverted torsional splitting patterns the relative orientation of such displacements changes by π(cis-trans interchange) upon half the internal rotation converting two neighbor equivalent conformations (as in a staggered-eclipsed conformational conversion). The formation of the actual torsional splitting patterns in degenerate vibrational states of CH₃CH₃-type molecules depends on the joint effect of torsional Coriolis and head-tail coupling. The torsional Coriolis operator can tune pairs of levels to resonance for the action of typical head-tail coupling operators (torsion-dependent vibrational operators), depending on the values of the torsional Coriolis coefficients, generating vibrational states with either regular or inverted torsional splitting patterns and affecting the splitting magnitude. It is shown that operators with a sin3τ-type torsional dependence favor the formation of inverted splitting patterns. In less symmetric molecules torsional Coriolis coupling affects the torsional splitting patterns by the same mechanism as in CH₃CH₃-type molecules, but the torsion-dependent operators are different and their action is expected to be less effective. Typical anomalous perpendicular splitting patterns can be predicted for non-degenerate modes localized in a single molecular moiety, normal or with a component normal to the internal rotation axis, having fixed orientation in that moiety (as the C=O or C-H stretchings of acetaldehyde). Adopting a barrier-hindered torsional basis, where the lower torsional levels can be seen as vibrational states with quantum numbers v_τ exhibiting tunneling splitting, one finds that all operators generating matrix elements with Δv_τ=±1, or in general odd, work toward the formation of inverted splitting patterns, generating anomalous patterns.

The new linelist for the water vapor in the 14395-14407 cm^-1 region is created with a goal to use the refined line parameters in the atmospheric transmittance calculations. The refinements include i) the line assignments based on accurate line position and strength calculations, ii) new width and pressure shift calculated by semiempirical method, iii) the temperature exponents for each line. The calculation of the atmospheric transmission spectrum has been carried out in this region.

As part of a global analyis of the infrared spectrum of chloromethane, the region of the fifth polyad involving the upper states of seven interacting bands 2υ6, υ₂+υ₃, υ₃+υ₅, 3υ₃, υ₂+υ₆, υ₅+υ₆, 2υ₃+υ₆, from 1900 to 2600 cm^-1 has been re-investigated. More than 20 000 transitions for each isotopomer ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been assigned and fitted with a standard deviation better than 4 10^-4 cm^-1 close to the experimental precision. The present paper is focussed on the determination of the ground state constants of ¹²CH₃³⁷Cl by exploiting in a global theoretical model perturbation-allowed transitions already observed for ¹²CH₃³⁵Cl by Di Lauro and Alamichel (J. Mol. Spectrosc. 81, 390-412 (1980)).

We present a high-temperature version, CDSD-1000, of the Carbon Dioxide Spectroscopic Databank and the associated information system on the spectroscopy of the carbon dioxide molecule. The databank contains the line parameters (positions, intensities, air- and self-broadened halfwidths and coefficients of temperature dependence of air-broadened halfwidths) of the four most abundant isotopic species of CO₂. The reference temperature is T_ref=1000 K and the intensity cutoff is I_cut=10^-27 cm^-1/(molecule cm^-2). More than 3 million lines covering the 260-8310 cm^-1, 418-2454 cm^-1, 394-4662 cm^-1, and 429-2846 cm^-1 spectral ranges for ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹²C¹⁶O¹⁸O, and ¹²C¹⁶O¹⁷O, respectively, are included in to CDSD-1000. The line positions and line intensities have been generated within the framework of the method of effective operators. The calculations are based on global fittings of parameters of effective Hamiltonians and effective dipole moment operators to the observed data collected from the literature. The line widths and coefficients of temperature dependence of the line widths have been generated using a semi-empirical approach. Line-by-line simulations of several medium resolution high-temperature (T=1000-1550 K) spectra have been performed in order to validate the databank. CDSD-1000 is freely accessible via ftp://ftp.iao.ru/pub/CDSD-1000. An information system on the spectroscopy of carbon dioxide molecule based on CDSD databank (http://cdsd.iao.ru and http://cdsd.lpma.jussieu.fr) has been elaborated. It allows users to calculate absorption coefficients, absorption, transmittance, radiance in wide ranges of temperatures and pressure for defined isotopic abundance and path length. This system also allows for modeling of spectra recorded with different kinds of spectrometers at different resolutions.

The general expressions for intermolecular potential are obtained on the base of the symmetrical approach. The convergence of intermolecular potential representations to be used for practical relaxation parameter calculations is investigated. It is found the series of intermolecular potential over inverse orders of intermolecular distance are divergent. In this work the technique for the summing of divergent series is supposed. The vibrational dependence of intermolecular potential is analyzed.

Within the framework of the algebraic disturbance method for eigenvalues and eigenvectors using the projectors theory, a research into the structure parameters of molecules excited vibrations has been performed. For this purpose, the formulae for higher-order elements of tensor of vibrations form have been obtained, on the basis of which, in accordance with an order of disturbance theory, the changes in intramolecular dynamic parameters and coefficients of kinematic interactions of excited vibrational states form, and the change in the elements of matrix for the n-order of disturbance theory have been determined.

Vibration - rotation energy levels of diatomic molecules are usually represented as a power series on vibration (v+1/2) and rotation J(J+1) quantum numbers - Dunham series. These series can be slowly convergent or even divergent for highly excited states, therefor, one needs to use the special method of their summation (Refs.[1-8] in the reference list are an examples). In the present we report the application of the Generalized Euler Transformation - a method for divergent series summation, for calculation of vibration-rotation spectra of diatomic molecules.

The detailed spectroscope information about highly excited molecules and radicals such us as H⁺₃, H₂, HI, H₂O, CH₂ is needed for a number of applications in the field of laser physics, astrophysics and chemistry. Studies of highly excited molecular vibration-rotation states face several problems connected with slowly convergence or even divergences of perturbation expansions. The physical reason for a perturbation expansion divergence is the large amplitude motion and strong vibration-rotation coupling. In this case one needs to use the special method of series summation. There were a number of papers devoted to this problem: papers 1-10 in the reference list are only example of studies on this topic. The present report is aimed at the application of GET method (Generalized Euler Transformation) to the diatomic molecule. Energy levels of a diatomic molecule is usually represented as Dunham series on rotational J(J+1) and vibrational (V+1/2) quantum numbers (within the perturbation approach). However, perturbation theory is not applicable for highly excited vibration-rotation states because the perturbation expansion in this case becomes divergent. As a consequence one need to use special method for the series summation. The Generalized Euler Transformation (GET) is known to be efficient method for summing of slowly convergent series, it was already used for solving of several quantum problems Refs.13 and 14. In this report the results of Euler transformation of diatomic molecule Dunham series are presented. It is shown that Dunham power series can be represented of functional series that is equivalent to its partial summation. It is also shown that transformed series has the butter convergent properties, than the initial series.

Using the effective Hamiltonian suggested in (V.I. Perevalov, E.I. Lobodenko, and J.-L. Teffo, "Reduced effective Hamiltonian for global fitting of C₂H₂ rovibrational lines", Proceedings of Twelfth Symposium and School on High-Resolutions Molecular Spectroscopy. SPIE. 3090, 143-149, 1997) the global fitting of the vibration-rotation line positions of acetylene molecule in the spectral range 0 - 9700 cm^-1 has been performed. The effective Hamiltonian is based on the assumption of the cluster structure of vibrational energy levels. A set of 147 effective Hamiltonian parameters, which consists of 90 diagonal and 57 resonance parameters, has been fitted to 7291 line positions of 109 bands, collected from 10 different experimental sources. The RMS deviation of 0.0045 cm^-1 has been achieved.

The structures of AuCl₄^-, AuCl₃(H₂O) and [AuCl₂(H₂O)₂]⁺ complexes were calculated by different methods of quantum chemistry. Basing of the calculation results, Density Functional Theory (DFT) with exchange-correlation PBE functional was chosen as the best one.

The expression for the second - order transformed polarizability operator for non-linear X₂Y -type molecules is derived using the method of contact transformation. This operator is used for the calculation of ro-vibrational Raman cross sections of the H₂O molecule. It is shown that the ro-vibrational correction terms change the integral intensity of pure rotational lines significantly and the ν₂ band slightly. The vibrational dependence of the mean polarizability of H₂O is analyzed in the calculation of integral intensity of one and two quantum bands.

One of the features of the H₂S molecule is quite weak intensity of the fundamental bands. Another feature is anomalous distribution of intensity over branches and its dependence on the rotational quantum number K. Correctly calculated parameters of the dipole moment function for the H₂S molecule allowed us to estimate the first and second rotational corrections in the transition moment operator for the fundamental bands. The calculated corrections appeared from the vibration-rotation coupling well reproduce the unusual intensity pattern of the P, Q and R branches in the H₂S molecule.

The work is aimed at building systematic links between accurate intra-molecular potential energy surfaces (PES) and effective rovibrational Hamiltonians for polyads of near degenerate vibrational states. A specialized computing package MOL_CT of formal rovibrational calculation developed for this purpose for a semi-rigid polyatomic molecule is presented. The general algorithm of high-order calculations, computer implementation and ordering issues are discussed. The package contains a suite of routines for PES and dipole moment surfaces (DMS) analysis, coordinate and axes transformations, change of operator representations, commutator calculations and term reductions. This allows a systematic computer assisted construction of effective rovibrational Hamiltonians for successive polyads starting with a PES for nuclear motion in a give electronic state. Some applications to asymmetric-top triatomic C_2v and C_s molecules with examples using recent accurate PES of water and ozone are briefly discussed.

The potential energy function of the ozone molecule empirically optimised to the largest set of spectroscopical high-resolution data of nine isotopomers ¹⁶O₃, ¹⁶O¹⁶O¹⁸O, ¹⁶O¹⁸O¹⁶O, ¹⁶O¹⁸O¹⁸O, ¹⁸O¹⁶O¹⁸O, ¹⁸O₃, ¹⁶O¹⁶O¹⁷O, ¹⁶O¹⁷O¹⁶O, and ¹⁶O¹⁷O¹⁷O used for this purpose so far is reported. The average accuracy of vibrational calculations for about sixty measured bands for nine isotopic species up to 3800 cm^-1 is about 0.02cm^-1. Reported variational calculations of high-J rovibrational states show a comparable accuracy up to J=45 for fundamental bands. The related global predictions were found very useful for the band and isotopic assignments of dense and complicated ¹⁸O enriched spectra recorded in Reims University and containing overlapping bands of six ¹⁸O enriched ozone isotopomers simultaneously.

Broadening coefficients for the ν₄ fundamental band of carbon tetrafluoromethane, CF₄, have been measured for the systems with argon, helium and nitrogen. Broadening coefficient behavior is similar to that previously reported for linear molecules: they coincide for P and R branches; the m-dependence in case of argon is sharper than that for helium. The broadening for nitrogen and helium are practically the same but the values for nitrogen are scattered around the general tendency. Q-branch broadening is also discussed. Our experimental data permitted us to evaluate the line intensity distribution and integrated intensity of the band.

To study the role of the off-diagonal imagery part of the relaxation matrix in the bandshape formation, the phase factor exp(-iα) has been introduced into empirical ECS expressions for the basic cross-section calculations. Analyzing the high-density 3v₃ CO₂ bandshapes in CO₂ - Ar gas mixtures, which are extremely sensitive to details of the line mixing effect, we have found that the off-diagonal imagery part of the matrix causes the sufficient shift of the band. Moreover, it causes decreasing the maximum of the branch R and increasing the maximum of the branch P. These effects correspond to the deviations between the measured and ECS calculated band profiles obtained in Ref. 1. This analysis leads to conclusion that the neglect of the off-diagonal imagery part of the relaxation matrix can provide systematic deviations of calculated spectral bandshape from observed one.

Nuclear magnetic resonance (NMR) of some nuclei (e.g. ¹H, ¹³C, ¹⁹F, ²⁹Si and ³¹P) gives strong signals which allow one for analytical investigations of gaseous compounds. The other magnetic nuclei have low natural abundance or/and contain electric quadrupole moments and therefore they are less suitable for such NMR applications. In our laboratory we have developed new experimental techniques which permit us to monitor several micrograms of chemical compounds in the gas phase. For the first time we have observed ¹⁷O and ³³S NMR spectra of gaseous compounds at the natural abundance as a function of density. We have also found density-dependent spin-spin coupling constants in many molecules. We could extend our gas-phase studies on molecules which exhibit strong intermolecular interactions and are liquids at room temperature. All the latter NMR experimental results obtained for gaseous mixtures are reviewed in this paper.

The values of the binary absorption coefficient μ₁₂ for an O₂ - Ar pair in the region of the Herzberg photodissociation continuum (200 - 230 nm) have been measured in the temperature range 295 - 120 K. It was found that for the temperatures from 295 K to 160 K the values of μ₁₂ demonstrate rather weak temperature dependence, while as the temperature decreases from 160 K to 120 K, the values of μ₁₂ increase by ~ 15%. Transition dipole moment function of exponential type was proposed to describe the observed temperature dependence of the values of the binary absorption coefficient μ₁₂ for an O₂ - Ar pair in the Herzberg III band of oxygen. Comparison of the temperature dependences of the binary absorption coefficients for an O₂ - Ar pair and for an O₂ - O₂ pair was carried out.

To calculate H₂O and CO₂ line broadening and shifting induced by nitrogen pressure the impact theory has been modified on the wider use of empiric data by introducing of the additional parameters taking into account the trajectory bending, effects of vibrational excitation, corrections to the scattering matrix obtained from the perturbation theory, etc. Model parameters were determined by fitting the broadening coefficients to experimental data. This allows sufficiently accurate prediction of the parameters of line profiles, which were not measured. Our calculated data are in satisfactory agreement with the measurements. The measured broadening coefficients also show the same trend as the calculated ones. According to developed approach the numerous calculations were performed, which allow one to make the conclusion that the calculations performed by our semiempiric method give reasonable description of water vapor and carbon dioxide line parameters induced by nitrogen pressure. As in our previous work on the water vapor line shifts in the R-branch of the v₂ band we have analysed the J-dependence of the halfwidths in a wide range of quantum numbers (up to J=15). The analysis shows that the halfwidths dependence as a function of the rotational quantum numbers have a more complicated character than it was assumed earlier. The halfwidths have an overall tendency to decrease with J for low K_a quantum numbers, but they are stable or even slightly increasing with J for large K_a.

The numerical calculation of self-broadening coefficients, shifts (δ) or half-widths (γ) leads to more than 3500 values for δ and γ for a ro-vibrational band of (formula available in paper). In the present work the analytical models for half-widths (formula available in paper) of H2O molecule (self-broadening case) are presented and discussed R is the set of rotational quantum numbers for initial, and final, states for the transition (formula available in paper). The models (available in paper) depend on the adjustable parameters, which may be determined for a given set of experimental data for γ. The self-broadening coefficients, shifts (δ) and half-widths (γ), were calculated for the first 10 vibrational bands and for the high values of (formula available in paper) molecule. The Robert Bonamy scheme ¹ was used. For (formula available in paper) band the values of δ and γ were calculated for the temperature 300 less than or equal to T less than or equal to 850 K with the step 50 K. The calculated values were compared with those obtained in a number of experimental studies.

Centre line shifts depending on the temperature are calculated using Anderson theory for water vapour induced by H₂O and N₂ pressure. It is shown, that center line shifts increase when the temperature decreases. Atmospheric depths for some altitudes were calculated. It is found, that the error of atmospheric absorption can reach 15% at the altitude 3 km, when the line shift temperature dependence is not taken into account.

General analytical expressions for non-diagonal matrix elements of intermolecular potential operator are found using the theory of linked ordering schemes¹ for ro-vibrational interactions. Non-diagonal matrix elements corresponds the long range electrostatic interactions in the system H₂O-H₂. Earlier the diagonal matrix elements of intermolecular potential operator were obtained. It is calculated the influence of the vibrational anharmonism on the non-diagonal matrix elements of intermolecular potential does not exceed 12%.

A near-infrared diode laser spectrometer was used under laboratory conditions to measure the H₂O line strengths and shifts by H₂ and He pressure near 1.39 μm. The hydrogen and helium broadened half-widths and shifts were measured for 5 transitions. These lines from the v₁ + v₃ and 2v₁ bands were selected because they are used for the “Spectrometre a diodes lasers” SDLA spectrometer (France) and to complete a set of isolated and quite strong lines with different J parameters. The experimental and calculated data are compared based on the semiempirical approximation in the absorption line broadening and shift. The helium pressure-induced shift coefficients and the hydrogen pressure-induced shift coefficients have opposite signs.

To model the signals of magnetic and frequency scanning of the rarefied gas, the problem of resonant interaction of two monochromatic waves and particles with active transition J = 0↔J = 1 in stationary magnetic field is solved by method of density matrix. The resonance with the sign depending on gas pressure, waves’ intensity and magnetic field strength was found for the system with a split ground state. Solution of wave equations for slow amplitudes.

Neutral and negatively charged individual ozone molecule and its complexes with up to eight water molecules are modeled in the MCQDPT/CASSCF/6-31++G** approximation. The results of adiabatic interaction of the dissociation products of ozone in the third and two higher excited electronic states with a water molecule and small water clusters are considered. Two alternative channels leading to the formation of OH or HO₂ radicals in a O(¹D)+H₂O system are found. The correlation diagram of the low-lying states of ozone is accordingly modified. The main product of the interaction between a singlet oxygen atom and a water cluster is determined to be hydrogen peroxide molecule. The problem of the excess electron localization by ozone in the presence of water molecules is also considered. An increase in the electron affinity of the neutral system and the electron detachment energy of the anion is treated in terms of a semiclassical solvation model.

The tunable blocking filter for the laser bigarmonic spectrometer is described. The filter prevents damage of the photoreciever CCD cells by the power optical beam. The calibration of the filter is performed by the automated procedure that speed - up the process and give the ability to check the adjustement of the interferometer of the filter avoiding it’s disassembling from the optical installation of the spectrometer. A group of laser spectroscopy specialists of the Institute of Atmospheric Optics has developed a laser spectrometer with a bigarmonic source for experimental investigation of the responce of molecular media exitied by bigarmonic optical field and verification of the hypothese about generation an optical field in these media. The spectrometer consists of: a) tunable laser based on two alumoittrium heads and frequency multiplicators, b) optical installation and gas probing cell, c) diffraction spectrograph (symbols available in paper) and linear CCD photoreceiver ILX-511, d) CAMAC modules, the computer and proper software. Peculiarity of described scheme consist in the necessity to register reemission coaxial with the pumping field. The wavelength of investigated reemission signal is close of the halfsum of the wavelength of the pumping bigarmonic. To avoid falling intense light on CCD device, which can physically damage photorecieving cells or, as minimum, completely mask usefull signal, it is necessary to mount an blocking optical filter into optical installation of the spectrometer. The filter have to provide continiuous blocking (when laser emitter tunes in diapasone of Δλ_1,2 ≈ 18526 ± 4 cm^-1) of the baffled components of the bigarmonic pumping. The present work is aimed to developing, preparing and testing such tunable rejecting filter. The Fabri - Perout interferometer was choosed as base element of the optical filter. The interferometer must be tuned to place next transmission maximum near the frequency of the investigating signal. In that way it is necessary to provide: a) optical conjugation of the interferometer with a gas probe cell and forming parallel optical beams, b) the possibility to tune the basis of the interferometer synchronously with the laser emitter tuning. To conjugate the interferometer with the cell and to form the proper optical beam, an optical scheme consisting from the lense L1 with the focal distance F₁ = 150 cm, and the telescope T equipped with a microobjective was mounted before the interferometer. After the interferometer, an diaframe (formula available in paper) and the lense L2 with the focal distance F₂ = 61 cm was mounted. Tuning of the interferometer (we’ve used an hook-up specimen of the interferometer by “NPO ANGSTREM”, Novosibirsk) is performed by constant voltage (0 ••• 150V) passed into piezoceramic plates. The voltage level is adjusted by the computer via CAMAC’s ADC device and voltage former. Sience given interferometer does not contain any thermo- and barostabilisaztion facilities and it’s parameters are greatly varying on time, it is not enough to adjust defined voltage level to operate with it. It is necessary to check interferometer’s adjustment and to prove it’s amplitude - frequency characteristics every time before working with the filter. The follows methodic and automated procedure are used in order to calibrate the filter and to proove the adjustments of the interferometer without it’s disassembling:

The grating spectrometer operating in near infrared and visible spectral regions with photoregistration system for the room and high temperature spectra investigations is presented. The spectrometer allows to investigate the absorption spectra with the spectral resolution of 0.036 cm^-1 and the precition of the line position of 0.003 cm^-1. Absorption spectra of the atmospheric air was recorded.

A fast method is offered for calculation of Voight spectral absorption line contour. A line profile is represented by a sum of terms of an absolutely converging series, containing undimensioned parameters a and b, connected with a property of the absorbing molecule, atmospheric temperature and pressure. The value b changes in a large limit from zero at the line center to 1000 and more at far wing of the line. The value a, describing a ratio of the Lorenz and Doppler effects, changes from a value ~5 near the surface of the Earth to 10^-5 in the stratosphere. Twenty terms of series ensure the high accuracy of the approximation for values b ranging from 0 to 5. The deviation from accurate Voight contour formula is less than 4*10^-4 or 0.04%. However, a large b value implies increase the number of terms, and the computing time increases accordingly. Numerical integration of Voight formula by Gauss-Hermite quadrature is simple, fast and accurate calculation for a value b> 5. In this case the deviation from accurate Voight formula is less than 2*10^-5 or 0.002%. Using the proposed approximation of the Voight profile line, the atmospheric transmission function was computed for the path Sun- satellite represented as a net of tangent heights relative to the Earth’s surface up to 100 km with 1 km step. The computation method involves 29 spectral channels of the water absorption region (933-959 nm) and 14 channels of the molecular oxygen absorption region (758-771 nm). The computations were performed for certain profiles of H₂O, O₂, temperature and pressure. The computations results were compared with experimental data.

At present some differences are observed between measured and calculated fluxes of solar radiation at the Earth’s surface. According to recent investigations these differences correlate with columnar water vapor. The results of calculation of the contribution of numerous weak absorption lines of water vapor, which usually are not taken into account as applied to atmospheric radiation problems, to the irradiance of the Earth’s surface and spectral brightness of sky are considered. Spatial-angular brightness was modeled in several spectral intervals of near IR and visible ranges at different vision directions and Sun positions. Irradiance of the Earth’s surface was estimated in the range of 4000-20000 cm^-1 under different aerosol conditions. It was performed comparative calculations for the HITRAN2000k spectral lines database and Partridge-Schwenke data. The calculated results have shown that the neglect of the contribution of weak absorption lines of water vapor in the near IR and visible regions can lead to errors (to 2% in the 100 cm^-1 intervals) in calculation of the diffuse radiation.

Atmospheric gas tunable diode laser (TDL) monitoring scheme is sensitive, local, real-time and portable. The traditional spectrophotometric methods have more performances for gas analysing, but are slow in response in high spectral resolution scheme and depend on influences by different gas species. Local measurements of small atmospheric gas components concentration (CH₄, CO, etc.) with diode-laser spectrometers are widely used in various of science and technical applications. An inverse task is usuallu solved by the correlation method (using all the measurement wavelengths) or other methods (for example, the method of fitting of the recorded spectrum under modelling). Each of these approaches has restrictions on retrieving connected with the features of measurement methods used in practice. This report, the results of the different inverse methods for retrieving the methane concentration from the data of a diode-laser spectrometer working in the NIR spectral range are analyzed. The methane diode-laser detector has a reference cell (with the known methane concentration) and a cross-flow cell (atmospheric air) as shown in Fig.1. The program of control and data processing of measurements is written with help of LabView software.

The virial coefficient data of various components of atmosphere are interesting because permit to evaluate a deviation from ideal gas model. These data may be useful while investigating the clusters generation and determination their contribution in absorption. The second cross virial coefficient B_aw for system ((nitrogen water)) has been calculated form +9°C to +50°C using the last experimental data about water vapor mole fraction. The reliability of this coefficient has been tested by analysing of errors sources and by comparing the results with other available experimental data.

A new standard installation has been developed to provide capability for calibration, testing and research of water content in such gases as atmospheric air and its components with high uncertainty at temperature from +5°C to +60°C and pressure from 0.1 MPa to 10 MPa. The humid gas has been produced by generator and then the water vapor mole fraction is measured by hygrometer.

The paper presents the calculation results for an optical system, used in a currently developed camera. The system transfers particle images of the volume under study to the region of holographic imaging. The calculation parameters are image location, resolution and adjustment tolerance.

The spectra of four substances with both similar and different absorption spectra in the region of 3-4 m were recorded. The proof is resulted that close IR region (3-4 mm) become informative at processing of spectra by the least - square method. The measurements were made on a spectrometer SA - 2 and IRS - 31.