Rapid vibrational quenching of CO(V) by H2O and C2H2

Rapid relaxation of vibrationally excited carbon monoxide molecules by H2O and C2H2 has been studied by time-resolved Fourier transform infrared emiss ion spectroscopy. The CO(upsilon) molecules were prepared by the laser-indu ced chemical reaction of CHBr3 with O-2. The temporal vibrational populatio ns of CO(upsilon) are deduced from the time-resolved spectra. For H2O, eigh t relaxation rate constants of CO(upsilon = 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 (x10(-13) cm(3) molecule(-1) s(-1)), respectively. For C 2H2, three rate constants of CO(upsilon = 1-3) are deduced to be 2.0 +/- 0. 1, 6.0 +/- 0.5, and 9.4 +/- 2.0 (x10(-13) cm(3) molecule(-1) s(-1)), respec tively. The excited CO(upsilon) molecules possibly transfer their vibration al energy to the nu(2) vibational modes of H2O or C2H2. The rapid relaxatio n of CO(upsilon) may be caused by many vibrational impacts in a transient h ydrogen-bonded complex. Ab initio calulations are carried out for the CO-H2 O and CO-C2H2 complexes. Theoretical calculations are also performed for th e quenching rate constants based on both SSH theory and the V-V,R model.