Time-resolved infrared fluorescence studies of the collisional deactivation of CO2(0001) by large polyatomic molecules

Abstract

Abstract The time-resolved infrared fluorescence (IRF) technique has been used to study the vibrational deactivation of CO 2 (00 0 1) by large polyatomic molecules at ambient temperature (295 ± 2 K).The excited CO 2 molecules were prepared by direct pumping with the P(21) line of a pulsed CO 2 laser at 10.6 μm. The bimolecular rate constant for deactivation by CO 2 was determined to be (0.353 ± 0.026) × 10 3 Torr −1 s −1 , in excellent agreement with previous work. The rate constants for deactivation by the large polyatomic molecules, c-C 6 H 10 , c-C 6 H 12 , C 6 H 6 , C 6 D 6 , C 7 H 8 , C 7 D 8 , C 6 H 5 F, p -C 6 H 4 F 2 , C 6 HF 5 and C 6 F 6 , were found to be (143 ± 18), (150 ± 12), (120 ± 4), (238 ± 9), (140 ± 5), (234 ± 15), (121 ± 7), (132 ± 23), (132 ± 12), and (94 ± 5) × 10 3 Torr −1 s −1 , respectively. Experimental deactivation probabilities and average energies removed per collision are calculated and compared. There is little difference in deactivation probabilities between the acyclic ring compounds and their aromatic analogues but the perfluorinated compound, C 6 F 6 is clearly less efficient than its hydrocarbon analogue, C 6 H 6 . The perdeuterated species, C 6 D 6 and C 7 D 8 show considerably enhanced deactivation relative to the other species, probably as a result of near-resonant intermolecular V-V energy transfer.