Translational and rotational excitation of the CO{sub 2}(00{sup 0}0) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene: Evidence for impulsive collisions accompanied by large energy transfers
- Department of Chemistry and Columbia Radiation Laboratory, Columbia University, New York, New York 10027 (United States)
The relaxation of highly vibrationally excited perfluorobenzene (C{sub 6}F{sub 6}) by collisions with CO{sub 2} molecules has been investigated over the temperature range 243{endash}364 K using diode laser transient absorption spectroscopy. Particular focus is placed on understanding both the dynamical features and the kinetics of collisions which are accompanied by large energy transfers into the CO{sub 2} rotational and translational degrees of freedom. Vibrationally hot perfluorobenzene (E{sub vib}=41822 cm{sup {minus}1}) was prepared by 248 nm excimer laser pumping, followed by rapid radiationless transitions to the ground electronic state. The nascent rotational population distributions (J=64{endash}80) of the 00{sup 0}0 ground state of CO{sub 2} resulting from collisions with hot perfluorobenzene were probed at short times following the excimer laser pulse. Doppler spectroscopy was used to measure the distributions of CO{sub 2} recoil velocities for individual rotational levels of the 00{sup 0}0 state. In addition, the temperature dependence of the state resolved, absolute rate constants for collisions populating high J states of CO{sub 2} was determined. The rotational distributions, distributions of recoil velocities, and quenching rates for production of CO{sub 2} high J states (J=64{endash}80) exhibit a very weak temperature dependence. The slight temperature dependence indicates that CO{sub 2} molecules which scatter into high J states of the ground vibrationless level originate from rotational levels near the mean of the pre-collision thermal rotational distribution. A gap law model is used to estimate the probability of collisions which are accompanied by large energy transfers yielding values less than 2{times}10{sup {minus}5}/cm{sup {minus}1} for {Delta}E{gt}2000 cm{sup {minus}1}. {copyright} {ital 1997 American Institute of Physics.}
- DOE Contract Number:
- FG02-88ER13937
- OSTI ID:
- 554233
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 17 Vol. 106; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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