Diode laser probing of the high-frequency vibrational modes of baths of CO2, N2O, and CO excited by relaxation of highly excited NO2

Abstract

Quenching of highly excited vibrational states of NO2 in baths of CO2, N2O, and CO has been investigated. Dilute NO2 mixtures were excited by a pulse from an excimer pumped dye laser operating at 495 nm. The ν3 antisymmetric stretching modes of CO2 (2349 cm−1) and N2O (2223 cm−1) and the v=1 level of CO (2143 cm−1) were probed with continuous wave IR diode lasers. The amount of energy transferred from excited NO2 to the ν3 modes of both CO2 and N2O was found to be 3%±1% of the original excitation energy. On the other hand, a smaller amount of energy (0.9%±0.3%) was deposited into the CO vibrational mode for NO2 contained in a dilute CO bath. These results support a picture of very inefficient transfer from high energy states of donor molecules to the high-frequency vibrational modes of small bath molecules. Differences in the efficiency of energy reception by the high-frequency modes of these three molecules scale roughly as the infrared transition moments for the bath states indicating the importance of resonance effects in the energy transfer process, but a combination of short- and long-range force mechanisms is probably necessary to account for the observed differences.