Proceedings Volume 2124

Laser Techniques for State-Selected and State-to-State Chemistry II

John W. Hepburn
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Proceedings Volume 2124

Laser Techniques for State-Selected and State-to-State Chemistry II

John W. Hepburn
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 17 June 1994
Contents: 8 Sessions, 45 Papers, 0 Presentations
Conference: OE/LASE '94 1994
Volume Number: 2124

Table of Contents

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Table of Contents

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  • Reaction Dynamics
  • Laser Coherent Control I
  • Laser Coherent Control II
  • Laser Diagnostics for Combustion
  • Laser Spectroscopy of Radicals
  • Spectroscopy of Clusters I
  • Spectroscopy of Clusters II
  • Poster Presentations
Reaction Dynamics
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Time-resolved infrared absorption studies applied to the study of radical plus molecule reactions
Gregory A. Bethardy, Frederick J. Northrup, Robert Glen Macdonald
The reaction of the cyano radical (CN) with ethane (C2H6) was studied using time resolved infrared absorption to monitor the product hydrogen cyanide (HCN) in individual ro-vibrational states. Pulse laser photolysis was used to provide an initial excess of the CN radical and the time dependence of individual ro-vibrational states of the high frequency antisymmetric stretching mode of HCN (0,0,v3) was followed. These experiments reveal that the initial product state distribution of HCN is not highly excited in the HCN(0,0,v3) vibrational manifold.
Photochemistry of the N2O-H2O complexes produced in supersonic jets
Ichiro Hanazaki, Hong-Lae Kim, Masao Takayanagi
We have studied 193 nm photodissociation of N2O(DOT)H2O complexes produced in a supersonic jet resulting in the reactant-pair reaction N2O(DOT)H2O + hv yields 2OH + N2. Measured internal energy, and spin-orbit and (Lambda) -doublet distributions in OH by laser induced fluorescence suggest a reaction scheme much different from the corresponding bimolecular reaction, O(1D) + H2O yields 2OH, observed in bulb experiments. The reaction should occur indirectly with early escape of N2 and proceed slowly in a relatively long-lived intermediate O(DOT)H2O.
Reaction of oxygen atoms with hydrocarbon monomers and clusters: the power of state-selectivity
Yoram Hurwitz, Yinon Rudich, Ron Naaman
Reactions of O(1D) with hydrocarbon monomers and clusters were investigated by a crossed molecular beam experiment applying laser induced fluorescence for the detection of the OH product. The rotational, spin-orbit and (Lambda) -doubling state populations were analyzed. Based on this information the mechanisms for the reactions of O(1D) with methane, propane and their clusters were established. Nonstatistical distributions are observed even for reactions of large clusters. These are discussed in terms of non-adiabatic effects induced by the long lived collision complex. Effect of the initial rotational temperature of the reactants on the energy distribution in the products is also presented.
Rotationally inelastic scattering of hydrogen fluoride as probed by a hydrogen fluoride chemical laser
Mark Keil, Leslie J. Rawluk, Millard Alexander, et al.
Rotationally inelastic collisions of HF are studied using a crossed molecular beams apparatus. We observe a rotational rainbow effect for highly excited rotational states, corresponding to strongly repulsive scattering of Ar off the repulsive core of the HF. In addition, we observe a novel `shoulder' for scattering into the rotationless state.
Two-color sub-Doppler double resonance: a spectroscopic method of obtaining the differential cross-section
Anthony J. McCaffery, Jon P. Richardson, Ruth J. Wilson, et al.
We describe a wholly spectroscopic technique in which the state-to-state differential scattering cross-section is determined for rotationally inelastic atom-molecule collisions. The method uses two single frequency tunable dye lasers in a sub-Doppler double resonance experiment. The method has the added advantage that dependence on initial velocity may be determined. The method is illustrated for the case of rotational transfer in Li2 - Xe collisions.
Doppler spectroscopy: a powerful tool for studying molecular collision dynamics
Jean-Michel Mestdagh, J. P. Visticot, Arthur G. Suits
The present review describes the application of Doppler spectroscopy to studies in collision dynamics. The method was originally introduced by Kinsey. We used it to obtain angular and velocity distributions of Ba(6s6p1P1) atoms scattered in the 6s6p3P2 level by collisions with Argon and simple molecules. After a short review of our recent work, we outline those areas where Doppler spectroscopy is a valuable tool (sometimes the only tool) for exploring gas phase collision dynamics. In particular we make clear the Doppler spectroscopy should not be considered as alternative but rather as complementary to the standard way of measuring differential cross sections where a rotating mass spectrometer rather than laser induced fluorescence is used to detect the scattered particles.
Laser Coherent Control I
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Control of molecular photodissociation via frequency tuning of intense laser fields
Zhidang Chen, Moshe Shapiro, Paul W. Brumer
We show that control over product ratios and channel specific line shapes in molecular photodissociation can be resulted from quantum interference effects which can be manipulated by varying the frequencies, instead of the relative phase, of two intense laser fields.
Experimental investigations of coherent control
Daniel S. Elliott, Ce Chen, Yi-Yian Yin, et al.
The potential of using interferences between transition amplitudes for the coherent control of photoionization rates and of asymmetric photoelectron angular distributions has been demonstrated previously. Current efforts in our laboratories are directed toward control of photoionization of NO, and on control of photoionization channels in atomic barium. This latter system is, of course, much simpler than a molecular system, and thus may provide better insight into the mechanisms involved. We will discuss our investigations of the effects of nonlinear coupling, absorption, and dispersion of the laser beams on their propagation through dense media, as observed via interference effects. Laser band structure effects and the effect of Doppler broadening will also be discussed.
Robust approaches to laser-selective chemistry and quantum molecular control
An absorption cell inside a Sagnac interferometer shapes laser pulses optimized to specific molecules, and a new acousto-optic pulse shaping technique provides improved flexibility for generating the complex waveforms needed for chemical applications.
Control of quantum dynamics: issues and alternatives
This paper gives an overview of the logic behind current conceptual issues directed towards controlling quantum phenomena. The role of theory to translate these concepts into laboratory designs will be highlighted, along with an explanation of the complexities of achieving realistic designs. As a result, it will be argued that closed-loop feedback control of quantum dynamics in the laboratory is not only feasible, but will typically be a necessity for the achievement of practical control over quantum phenomena.
Laser Coherent Control II
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Superpositions of chiral amplitudes
Jeff A. Cina, Robert A. Harris
A recent analysis has suggested that a version of femtosecond pump-probe spectroscopy, in which both pulses are themselves optical phase-controlled pulse pairs, would be useful in preparing and measuring chiral coherences. These coherences are absent in a racemic mixture or an incoherent sum of left- and right-handed states. Here we discuss the preparation of chiral coherences and the observation of their degradation via interaction with a low temperature medium.
Optimal control of product selectivity in the reations of polyatomic molecules: a reduced space analysis
Stuart A. Rice, Meishan Zhao
The methods proposed for the control of the dynamical evolution of a quantum system are, in principle, applicable to molecules of any size. However, the complexity of the description of the states of a molecule with many degrees of freedom has the practical consequence that obtaining the information necessary to design a control field is very difficult. To overcome this difficulty we propose, for the case of enhancement of specific product formation in a unimolecular reaction, the use of a particular reduced description of the many body dynamics, namely, a constrained reaction path representation. The formalism for this scheme is sketched, and some of the consequences of the approximations used are briefly discussed.
Quantum control of electron dynamics
Jeffrey L. Krause, Kent R. Wilson, Yijing Yan
We present computational examples of the quantum control of electron dynamics in the time-domain. We use a general Liouville-space, density matrix formalism to predict the electric field that best drives a system to a chosen outcome, at a chosen time. The method is applicable, in principle, to atoms and molecules, and to gases, clusters, surfaces and condensed phases. In this work, we specialize to the control of radial electron wave packets in the hydrogen atom. We illustrate the method with two examples, a reflectron and a transient quantum nanostructure. In the reflection, we focus an electronic wave packet to have maximum overlap at a specified time with a Gaussian target localized in position and momentum, with the momentum directed towards the nucleus. In the nanostructure, we focus the wave packet onto a target that is double-peaked in position, with momentum directed away from the nucleus.
Laser Diagnostics for Combustion
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Optical diagnostics of diamond CVD plasmas
Jay B. Jeffries, George A. Raiche, Michael S. Brown
Chemical vapor deposition of diamond occurs in a dynamic reacting environment which is far from chemical equilibrium. Real time, in situ, non intrusive diagnostics of the reacting gas mixture are needed to develop and test models of the chemical mechanism of diamond growth. We demonstrate the use of laser- induced fluorescence to probe the rotational state distribution in diamond depositing dc-arc-jet plasma to infer the gas temperature which is required to model the chemistry. Compensation for collision dynamics of the laser-excited state plays an important role in the determination of accurate and precise gas temperatures.
Laser imaging of chemistry-flowfield interactions: enhanced soot formation in time-varying diffusion flames
Joel E. Harrington, Christopher R. Shaddix, Kermit C. Smyth
Models of detailed flame chemistry and soot formation are based upon experimental results obtained in steady, laminar flames. For successful application of these descriptions to turbulent combustion, it is instructive to test predictions against measurements in time-varying flowfields. This paper reports the use of optical methods to examine soot production and oxidation processes in a co-flowing, axisymmetric CH4/air diffusion flame in which the fuel flow rate is acoustically forced to create a time-varying flowfield.
Optical detection of CH3 during diamond chemical vapor deposition
David G. Goodwin, Nick G. Glumac, Evaldo J. Corat
Measurements of CH3 have been made using resonance-enhanced multiphoton ionization (REMPI) in two different diamond growth environments. Spatial profiles of methyl above the substrate have been measured in a filament- assisted reactor, which show that the CH3 concentration is depleted near the substrate. The CH3 concentration at the substrate shows an approximate Arrhenius dependence on substrate temperature below 1000 K, characterized by an activation energy of 4 kcal/mole. Methyl measurements were also made in 35 Torr hydrogen/oxygen flame into which methane is injected near the substrate. Radial profiles of methyl, acquired using REMPI, and of CH4, acquired using sampling mass spectroscopy, are in good qualitative agreement with the results of numerical simulations.
Laser Spectroscopy of Radicals
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Photoelectron spectra of organic radicals and biradicals
Cameron F. Logan, Eric S. J. Robles, Daniel W. Kohn, et al.
Data reduction for photoelectron spectra of transient organic reactive intermediates is demonstrated for the extraction of thermochemical information from poorly resolved spectra. Application to dichlorocarbene and the (alpha) ,3-dehydrotoluene biradical are shown.
Laser-induced fluorescence spectra of jet-cooled organometallic radicals
Terry A. Miller
Less than ten years ago, the gas phase spectroscopy of organometallic radicals was, except for diatomics and other closely related species, essentially non-existant. The situation changed dramatically with the reports of laser induced fluorescence (LIF) spectra of organometallic radicals by Bemath and co-workers. They prepared a number of species in a Brodia oven reactor wherein a metal vapor, produced from equillibrium heating of a metallic solid, is reacted with a suitable reagent to form an organometallic radical. The species produced were at ambient temperature or above and oftentimes their LIF spectra were quite congested; however, a number of very interesting observations were made concerning their electronic spectra and structure, and the foundation for future experiments was firmly laid. Somewhat after the promising experiments of Bernath and co-workers, our laboratory pioneered the production of similar organometallic radicals in a supersonic free jet expansion. The cooling of the organometallic radicals by the jet to a few degrees Kelvin greatly simplified many of their LIF spectra and allowed for detailed analysis.
Spectroscopy of vibrationally excited states of CCH
Yen-Chu Hsu
Vibrationally excited states of CCH radical, up to 5000 cm-1 above the ground vibrational level of the X2(Sigma) + state, have been studied by laser-induced fluorescence in both a flow cell and a supersonic beam expansion. CCH radical was generated by photolyzing acetylene with 193 nm laser light. Ten uv bands of parallel type transitions have been assigned as the transitions from X(0,v2,0) (v2 equals 1, 3-11) to S (Kequals0) or U (Kequals1). Comparison between the experimental observations and ab initio calculations of the bending vibrational levels will be given.
Negative ion photoelectron spectroscopy of organometallic radicals: MCO and HMCO complexes of the first transition series
Peter W. Villalta, P. Thomas Fenn, Doreen G. Leopold
The effect of a input second-harmonic seed wave on the second-harmonic generation process is described. Experimentally, we demonstrate a 4.6-to-1 modulation depth imposed on the fluence of an intense 1.06 micrometers picosecond pulse by varying the relative phase of a weak second-harmonic control pulse under near phase-matched conditions. This transistor-like action is based on quadratic nonlinearities in KTP.
Nonresonant two-photon pulsed field ionization studies of organosulfur molecules and radicals
C.-W. Hsu, David P. Baldwin, Chung-Lin Liao, et al.
Threshold photoelectron (PE) spectra for CH3SH, CH3S, and SH have been measured using the nonresonant two-photon pulse field ionization (N2P-PFI) technique. The rotationally resolved N2P-PFI-PE spectrum obtained for SH indicates that photoionization dynamics favors the rotational angular momentum change (Delta) N < 0 with the (Delta) N value up to -3.
Spectroscopy of Clusters I
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Understanding barriers to internal rotation in toluene, phenylsilane, and their cations
Kueih-Tzu Lu, James C. Weisshaar
Threshold photoionization spectra of toluene+ and phenylsilane+ using the new pulsed field ionization technique resolve internal rotor states. As in the neutral S0 and S1 states, sixfold barriers to internal rotation are small in the cations, < 25 cm-1. Ab initio calculations support a donor-acceptor model that qualitatively explains why all sixfold barriers are small while some threefold barriers are much larger.
Role of solvent and vibrations on proton tunneling in clusters
Jack A. Syage
In this paper we present a theoretical framework for describing the role of solvent and vibrations on proton tunneling rates. Recent experiments indicate that excited-state proton transfer in ROH(NH3)n clusters (where ROH is 1-naphthol or phenol) occurs by a tunneling mechanism. Two previous models of proton tunneling are examined; one based on a solvent-independent bound- continuum potential and the other on a solvent-activated bound-bound potential. Here we extend the latter model to incorporate coupling of the proton to reactant and product vibrations. All three models are compared to experimental tunneling rates in clusters.
High-resolution spectroscopy of small transition metal molecules: recent experimental and theoretical progress on group 5 diatomics
Benoit Simard, Andrew M. James, Pawel Kowalczyk, et al.
Current understanding of spectroscopy and bonding in group 5 metal dimers is reviewed and new experimental and theoretical data are presented. In particular, density functional calculations on the lowest triplet and the lowest single state of VNb and on the ground state of the singly charged cations V2+, VNb+ and Nb2+ are reported and discussed for the first time.
Electronic spectroscopy and electronic structure of the smallest metal clusters: the diatomic 3D transition metal aluminides
Jane M. Behm, Michael D. Morse
A systematic study of the electronic spectroscopy, electronic structure, and chemical bonding has been initiated for the 3d series of diatomic transition metal aluminides. This report provides a review of the progress to date, with specific emphasis on AlCa, AlV, AlCr, AlMn, AlCo, AlNi, AlCu, and AlZn.
Structural dynamics of carbon- and metal- containing carbon clusters
David E. Clemmer, Martin F. Jarrold
A summary of recent studies of the geometries and structural dynamics of pure carbon and metal containing carbon clusters is given. For pure carbon clusters the bicyclic and polycyclic rings can be converted into either monocyclic rings or fullerenes. Formation of the monocyclic rings is driven by a decrease in the strain energy, while fullerene formation is driven by formation of the stable fullerene cage. Mechanisms which explain the formation of bicyclic and polycyclic rings, as well as the conversion of these into monocyclic rings and fullerenes are discussed.
Spectroscopy of Clusters II
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Optical absorption spectra of Ag8 and Ag20 in solid neon
Wolfgang Harbich, R. Kleiber, Y. Caloz, et al.
Ag8+ and Ag20+ have been produced by sputtering, mass selected in a quadrupole mass filter and deposited at 30 eV landing energies together with neon on a 5 K sapphire surface. The cluster ions are neutralized during the deposition process. In contrast to the other rare gases (Xe, Kr, Ar) no fragmentation has been detected. The absorption spectra show results very similar to the system Agn/Ar but are better resolved in the case for Ag8. The spectra are compared to gas phase photodepletion data and Nan.
Photodissociation spectroscopy of metal clusters: a status report
Douglas Cameron, Susanne Haupt, Julian Kaller, et al.
Photodissociation spectroscopy has been applied to the characterization of the electronic and geometric structure of cold silver cluster cations (Agx+, x < 22). Preliminary results are described.
Poster Presentations
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Mechanical mechanism for the ultrafast perturbation of electronic states in solution
Mark A. Berg, John T. Fourkas, Andrea Benigno
The interaction dynamics between a nonpolar solute (dimethyl-s-tetrazine) and a nonpolar solvent (n-butylbenzene) have been explored over a wide temperature range (40 K - 300 K). On the basis of the results, a new model based on mechanical interaction between solute and solvent is proposed. The dynamics consist of two distinct components. A subpicosecond component is linked to the phonon-like motion about the instantaneous liquid structure. The other component is related to structural reorganization of the solvent. The time scale of the structural dynamics is identical to the shear relaxation time of the solvent. A model in which the solvent responds as a viscoelastic continuum to the difference in size and shape of the solute in the ground and excited states is presented. It accounts for the existence and time scales of both solvation components.
Quantum-resolved vibrational energy transfer in Br2 B3II(Ou+)
Courtney D. Holmberg, Glen P. Perram
State-to-state vibrational energy transfer and electronic quenching in the lower vibrational levels, v' <EQ 3 of the B3II (Ou+) state of 79Br2 were investigated using spectrally resolved, temporally resolved laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated Br2 (B) vibrational levels were observed for Br2 and rare gas collision partners. Vibrational transfer is quite efficient in the non-predissociated levels and is adequately described by the Montroll- Shuler model for harmonic oscillators. A fundamental rate coefficient for vibrational transfer from v' equals 1 to v' equals 0, kv (1,0), was used to characterize vibrational relaxation.
New spectroscopy of free radicals produced by the reactions of fluorine and chlorine with diborane
Jeffrey W. Hudgens, Karl K. Irikura, Russell D. Johnson III
We report the first resonance enhanced multiphoton ionization (REMPI) spectra of the boron-centered free radicals, BF, BCl, B2, BF2 and atomic boron. These spectra were observed between 300 and 380 nm by two photon resonances with previously unreported Rydberg states that reside between 58000 and 65600 cm-1. The radicals were produced by chain reactions of fluorine and chlorine atoms in a flow reactor and ion signals were analyzed by mass spectrometry. The REMPI spectra BF, BCl, B2, and BF2 originate from 3s and 4s Rydberg states. The spectrum of boron atoms arises from a new np Rydberg series and from a nf Rydberg series.
Site propensities for HCl and DCl formation in the reaction of Cl with selectively-deuterated alkanes
Brent D. Koplitz, Yu-Fong Yen
Gas-phase hydrogen abstraction reactions involving Cl and selectively- deuterated propanes and isobutanes have been studied. Cl atoms are generated through the 351 nm photolysis of Cl2, and both the HCl and DCl products are detected via 2 + 1 multiphoton ionization at approximately 240 nm. Labelled compounds enable one to identify positively with individual reactive sties within a given target molecule. For propanes over the quantum states probed, DCl is formed with nearly equal probability independent of whether CH3CD2CH3 or CD3CH2CD3 is the target molecule. For HCl formation, Cl reacting with CH3CD2CH3 generates slightly more HCl than does Cl reacting with CD3CH2CD3. For Cl attacking labelled isobutanes, kinetic and/or steric effects appear to be significant. Overall, the results are discussed in terms of their implications for `site-specific' bimolecular behavior.
Laser-induced graft co-polymerization on the surface of polymer
Vadim B. Oshurko, A. A. Chistyakov, Yuri A. Bykovsky
The main problem in laser stimulation of selective (nonequilibrium) reactions in solids is to overcome the fast internal conversion which led to electronic states deactivation and heating with thermal dissociation. But sometimes it's possible to find a condition when the heating of surface is negligible but the intensity is enough to initiate multiphoton excitation of molecules. In present work the effect of direct (i.e. without sensitizers) graft co- polymerization under pulsed UV-laser radiation on the surface of polymer in gas atmosphere was found. Absorption, luminescent spectroscopy and time-of- flight mass-spectrometry were used as experimental methods as well as chemical analysis. The effect of co-polymerization shows nonlinear dependence on power density. It has been found that co-polymerization due to nonlinear nonthermal macromolecules dissociation on the surface and the excitation of molecules in gas phase play no role. Ion-exchange, properties of new material have been studied.
UV-laser control of macromolecules dissociation mechanisms on the surface of polymer
Vadim B. Oshurko, Yuri A. Bykovsky, A. A. Chistyakov
In present work experimental studies of macromolecules dissociation mechanism under short UV-laser pulses in a wide range of power density have been carried out. As experimental methods of time-of-flight mass-spectrometry and laser- induced fluorescence have been used.
Intracavity laser spectroscopy of flames: detection of oxygen atoms
Sergey Cheskis, S. A. Kovalenko
The absolute concentration of atomic oxygen in atmospheric pressure hydrogen/air flame has been measured using Intracavity Laser Spectroscopy based on a dye laser pumped by an argon-ion laser. Absorptions at the highly forbidden transitions at 630.030 and 636.380 nm were observed at an equivalent optical length of up to 10 km. The relatively low intensity of the dye laser avoids photochemical interferences that are inherent to some other methods for detecting atomic oxygen. Detection sensitivity is about 6 X 1014 atom/cm3 and can be improved with better flame and laser stabilization.
Laser control of photopredissociation by Cl2 by two color interference
Andre D. Bandrauk, Jean-Marc Gauthier, James F. McCann
A coupled equations approach based on a general artificial channel method is used to demonstrate two color laser coherent control of photopredissociation and photoionization in Cl2. Photopredissociation angular distributions illustrate the suppression of the corresponding transition in selective rotational states.
Augmented Lagrangian method for optimal laser control
Hai Shen, Jean-Pierre Dussault, Andre D. Bandrauk
We use penalty methods derived from Augmented Lagrangians coupled with unitary exponential operator methods to solve the optimal control problem for molecular time-dependent Schodinger equations involving laser pulse excitations. A stable numerical algorithm is presented which propagates directly from initial states to given final states. Results are reported for an analytically solvable model for the complete inversion of a three-state system.
Pulsed-laser ionization and dissociation of Mn2(CO)10
Yong-jun Wang, Ming-fei Zhou, Shi-min Shi, et al.
The pulsed-laser ionization and dissociation of dimanganese decacarbonyl, Mn2(CO)10, is investigated using time-of-flight mass spectrometry. Both positive and negative fragment ions are observed following pulsed laser irradiation of solid Mn2(CO)10 samples with a tunable dye laser at selected wavelength of 280 nm.
Photofragment imaging of angle-velocity distributions
R. A. Hertz, Jack A. Syage
Photofragment angle-velocity distributions are measured in a molecular beam using a new 2D imaging technique. We report on the detection of weak perpendicular transitions for CH3I A state photodissociation at 266 and 304 nm.
State-selected molecular ion-surface scattering: probing energetic and geometric effects in charge transfer and dissociation
J. S. Martin, J. N. Greeley, J. R. Morris, et al.
We have utilized resonance-enhanced multiphoton ionization in conjunction with ion optics to produce state-selected NO+(X1(Sigma) +, v equals 0 - 6, Etrans equals 8 - 80 eV) ions.
Spectroscopic studies of intracluster chemistry
Jong-Ho Choi, Mitchio Okumura
Infrared predissociation spectroscopy of ion-solvent clusters has allowed us to examine the effects of sequential hydration on the reactivity of cations such as NO+, NO2+, and protonated formaldehyde, H2COH+, stable gas phase ions which are known to undergo rapid reactions in aqueous solution. Our experiments demonstrate that these ions undergo hydration reactions at critical cluster sizes. The smaller clusters have spectra characteristic of H2O ligans bound to stable ion cores, but as the cluster size increases, there is a sudden onset for intracluster rearrangements, e.g. NO2+ + H2O yields H3O+ + HNO3 which occurs upon hydration with four water molecules. With this approach, we can probe microscopic aspects of solvent effects on chemical reactions including the hydration of carbonyls and acid-catalyzed hydrolysis of amides.
Autodetachment spectroscopy of a molecular anion using a diode laser
Ravi W. Marawar, Daniel C. Cowles, Ray E. Keeler, et al.
Autodetachment spectroscopy, a technique for studying molecular anions, has been applied to the past using color-center lasers or visible dye lasers. In the present work, the technique has been extended to employ a relatively weak diode laser. Laser radiation drives an infrared vibrational-rotational transition in the molecular anion NH-. The vibrationally excited anion autodetaches, and the resulting fast neutral is detected. The P1 (6.5, e- > e) transition in the fundamental (1 < -0) band of NH- has been observed near 2806 cm-1 with a signal to noise ratio of 15:1 with a 30-s averaging time. The present experiment has fewer than 500 ions of a single quantum state in the apparatus at once, interacting with 5 microwatts of laser power. Future instrumental improvements can yield orders of magnitude improvement in sensitivity.
Infrared and near infrared transient absorption spectroscopy of molecular free radicals
Trevor J. Sears, Ming T. Wu, Gregory E. Hall, et al.
Recent results obtained using absorption techniques with continuous wave lasers to measure vibrational and electronic spectra of small free radicals are reported.
New very sensitive double modulation techniques for the detection of high-resolution infrared absorption spectra of radicals, molecular ions, and excited states of stable molecules
Concepcion Maroto Domingo, Isabel Tanarro, M. M. Sanz, et al.
Two new double modulation techniques for infrared absorption spectroscopy of transient molecules are described. Both of them are based in the modulation in concentration of the unstable species and the modulation in amplitude of the laser radiation. One of the methods is specific for short lived transients; the first results obtained with it for the H3 + spectrum are given. The other one is more suitable for longer lived species; it has been applied to the study of the 113 band of CH3 and vibrational excited states of methane.
Coherent photodissociation-recombination dynamics of I2 isolated in matrix Ar and Kr
Ruben Zadoyan, Zhiming Li, Craig C. Martens, et al.
Time-resolved studies of photodissociation-recombination dynamics of I2 isolated in Ar and Kr matrices, are reported.