TRANSLATIONAL AND ROTATIONAL-EXCITATION OF THE CO2(00(0)0) VIBRATIONLESS STATE IN THE COLLISIONAL QUENCHING OF HIGHLY VIBRATIONALLY EXCITEDPERFLUOROBENZENE - EVIDENCE FOR IMPULSIVE COLLISIONS ACCOMPANIED BY LARGE ENERGY TRANSFERS
Ca. Michaels et al., TRANSLATIONAL AND ROTATIONAL-EXCITATION OF THE CO2(00(0)0) VIBRATIONLESS STATE IN THE COLLISIONAL QUENCHING OF HIGHLY VIBRATIONALLY EXCITEDPERFLUOROBENZENE - EVIDENCE FOR IMPULSIVE COLLISIONS ACCOMPANIED BY LARGE ENERGY TRANSFERS, The Journal of chemical physics, 106(17), 1997, pp. 7055-7071
The relaxation of highly vibrationally excited perfluorobenzene (C6F6)
by collisions with CO2 molecules has been investigated over the tempe
rature range 243-364 K using diode laser transient absorption spectros
copy. Particular focus is placed on understanding both the dynamical f
eatures and the kinetics of collisions which are accompanied by large
energy transfers into the CO2 rotational and translational degrees of
freedom. Vibrationally hot perfluorobenzene (E-vib=41 822 cm(-1)) was
prepared by 248 nm excimer laser pumping, followed by rapid radiationl
ess transitions to the ground electronic state. The nascent rotational
population distributions (J=64-80) of the 00(0)0 ground state of CO2
resulting from collisions with hot perfluorobenzene were probed at sho
rt times following the excimer laser pulse. Doppler spectroscopy was u
sed to measure the distributions of CO2 recoil velocities for individu
al rotational levels of the 00(0)0 state. In addition, the temperature
dependence of the state resolved, absolute rate constants for collisi
ons populating high J states of CO2 was determined. The rotational dis
tributions, distributions of recoil velocities, and quenching rates fo
r production of CO2 high J states (J=64-80) exhibit a very weak temper
ature dependence. The slight temperature dependence indicates that CO2
molecules which scatter into high J states of the ground vibrationles
s level originate from rotational levels near the mean of the pre-coll
ision thermal rotational distribution. A gap law model is used to esti
mate the probability of collisions which are accompanied by large ener
gy transfers yielding values less than 2X10(-5)/cm(-1) for Delta E >20
00 cm(-1). (C) 1997 American Institute of Physics.