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

The time-resolved infrared fluorescence (IRF) technique has been used to study the vibrational deactivation of CO2(0001) by large polyatomic molecules at ambient temperature (295 ± 2 K).The excited CO2 molecules were prepared by direct pumping with the P(21) line of a pulsed CO2 laser at 10.6 μm. The bimolecular rate constant for deactivation by CO2 was determined to be (0.353 ± 0.026) × 103 Torr−1 s−1, in excellent agreement with previous work. The rate constants for deactivation by the large polyatomic molecules, c-C6H10, c-C6H12, C6H6, C6D6, C7H8, C7D8, C6H5 F, p-C6H4F2, C6HF5 and C6F6, 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) × 103 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, C6F6 is clearly less efficient than its hydrocarbon analogue, C6H6. The perdeuterated species, C6D6 and C7D8 show considerably enhanced deactivation relative to the other species, probably as a result of near-resonant intermolecular V-V energy transfer.