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Proceedings Paper

Vibrationally excited benzene molecular cooling in supersonic beams
Author(s): V. N. Ishchenko; S. A. Kochubei; V. I. Makarov
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Paper Abstract

There were examined photoionization spectra of benzene cooled in supersonic molecular beams. Compounds of benzene vapor with several buffer gases were used -- He, Ne, Ar, Kr, N2, CH4. The photoionization was performed by frequency tuning KrF laser (linewidth 0.8 cm-1; tuning range 120 cm-1). The process is step-by-step, with the real intermediate level. The tuning range envelops two vibronic bands 6011011611 and 611103, belonging to electron transition 1A1g - 1B2u. The ionization spectrum is mainly dependent on the absorption spectrum at the first step. The both bands are hot, but nevertheless the ionization efficiency at supersonic beam conditions is rather high; it's caused by large 'gap' of vibronic temperature from rotational and translative ones. As it was experimentally defined with various buffer gases, that bands intensity relation varies too. This fact testify about vibronic cooling dependence on the sort of buffer. Besides, a significant difference in the bands envelope contour widths was discovered. That is rather unusual fact, as the band width mainly depends on rotative temperature in the low state (rotative band structure wasn't resolved in that experiments). Based on their data the rotative temperature estimation shows for benzene, that rotative temperature of molecules with excited 6th vibronic mode is always lower (approximately equals 4.5 K with Ne buffer), than molecules with 16th one (approximately equals 15 K at the same conditions). This fact was interpreted as the rotationally-vibronic interaction result. As degenerated 6th mode has vibrational angular momentum, which is absent in the 16th, degenerated as well, so rotative-vibronic interaction in the first case is significantly strong, and leads to levels splitting comparable with the rotative structure. As the result rotative levels density for 6th mode twice more. The interpretation moment for rotative relaxation, i.e., the time, or characteristic distance from the nozzle cut-off, where rotative relaxation in the molecular beam forming on translative temperature and molecular density as well as sublevels energy interval. The last is twice less for molecula with the excited 6th mode, that is the reason of their more intense rotative cooling.

Paper Details

Date Published: 21 October 1998
PDF: 7 pages
Proc. SPIE 3485, 11th International Vavilov Conference on Nonlinear Optics, (21 October 1998); doi: 10.1117/12.328296
Show Author Affiliations
V. N. Ishchenko, Institute of Semiconductor Physics (Russia)
S. A. Kochubei, Institute of Semiconductor Physics (Russia)
V. I. Makarov, Institute of Chemical Kinetics and Combustion (Russia)


Published in SPIE Proceedings Vol. 3485:
11th International Vavilov Conference on Nonlinear Optics
Sergei G. Rautian, Editor(s)

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