Rapid Vibrational Quenching of CO(V) by H2O and C2H2

Abstract

Rapid relaxation of vibrationally excited carbon monoxide molecules by H2O and C2H2 has been studied by time-resolved Fourier transform infrared emission spectroscopy. The CO(v) molecules were prepared by the laser-induced chemical reaction of CHBr3 with O2. The temporal vibrational populations of CO(v) are deduced from the time-resolved spectra. For H2O, eight relaxation rate constants of CO(v = 1−8) are determined to be 1.7 ± 0.1, 3.4 ± 0.3, 6.2 ± 0.6, 8.0 ± 1.0, 9.0 ± 2.0, 12 ± 3, 16 ± 6, and 18 ± 10 (×10-13 cm3 molecule-1 s-1), respectively. For C2H2, three rate constants of CO(v = 1−3) are deduced to be 2.0 ± 0.1, 6.0 ± 0.5, and 9.4 ± 2.0 (×10-13 cm3 molecule-1 s-1), respectively. The excited CO(v) molecules possibly transfer their vibrational energy to the ν2 vibational modes of H2O or C2H2. The rapid relaxation of CO(v) may be caused by many vibrational impacts in a transient hydrogen-bonded complex. Ab initio calulations are carried out for the CO−H2O and CO−C2H2 complexes. Theoretical calculation...