Rotationally specific mode-to-mode vibrational energy transfer in D2CO/D2CO collisions. II. Kinetics and modeling

C. P. Bewick, J. F. Martins, B. J. Orr*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

Time-resolved infrared-ultraviolet double resonance (IRUVDR) spectroscopy is used to study the kinetics of collision-induced rovibrational energy transfer between the v6 and v4 modes of D2CO in the vapor phase. As in paper I [J. Chem. Phys. 93, 8634 (1990)] of the series, attention rests on the existence of V-V transfer channels which are rotationally specific with respect to both J and Ka. Infrared excitation by the 10R (32) CO2-laser line prepares D2CO in two discrete rovibrational states, (J,Ka,Kc) = (11,4,7) and (7,2,6), of the v6 = 1 vibrational manifold. D2CO/D2CO collisions then disperse this selected population to various states of the (v4,v6) rovibrational manifold, through a combination of rotational energy transfer (RET) and v6 → v4 transfer. This yields an extensive range of (J,Ka)-resolved IRUVDR kinetic curves, demonstrating the collision-induced evolution of rovibrational population and enabling that evolution to be modeled by means of a master-equation approach. The features of the model of best fit are as follows: the dominant K a-resolved channel of v6→ v4 transfer is that with Ka= 4→6; accompanying J-resolved v6- →v4 transfer channels favor ΔJ = 0, with state-to-state rate constants scaling as J3.4; additional (J,Ka)-resolved v6→v4 channels allow a spread of J- and K a-changing V-V transfer. These features are consistent with the accepted mechanism of v6-→v4 transfer in D 2CO, involving enhancement by a combination of Coriolis coupling and rotor asymmetry perturbations. In addition to v6→v4 transfer, RET provides the predominant channels of collision-induced relaxation: J-changing RET is described by a conventional fitting law based on the energy gap |ΔE| for the state-selected molecule; Ka-changing RET favors even values of ΔKa and, contrary to previous expectations, is J selective with a propensity for ΔJ = 0. The physical implications of these results are discussed.

Original languageEnglish
Pages (from-to)8643-8657
Number of pages15
JournalThe Journal of Chemical Physics
Volume93
Issue number12
DOIs
Publication statusPublished - 15 Dec 1990

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