Vibrational relaxation of H2O from 295 to 1020 K

A laser induced fluorescence/heated flow tube method has been used to measure rate constants for vibrational relaxation of the coupled ν1 and ν3 stretching levels, the 2ν2 bending overtone level, and the ν2 bending level of H2O by H2O and rare gases from 295 to 1020 K. The probability per collision for self-relaxation of the coupled stretching levels decreased monotonically from 0.146 at 295 K to 0.055 at 1020 K. The probability for self-relaxation of the 2ν2 level decreased monotonically from 0.59 at 295 K to 0.32 at 947 K. The probability for self-relaxation of the ν2 level decreased with temperature from 0.26 at 295 K to 0.16 at 947 K. At all temperatures the dominant path for H2O self-relaxation was relaxation of the stretching levels to the bending overtone level followed by V→T,R relaxation of a single bending quantum to the bending fundamental level. Relaxation of all levels by He and Ar was approximately two orders of magnitude less efficient than H2O self-relaxation. The rate constant for relaxation of the H2O stretching levels by oxygen atoms was measured at 315 and 520 K, and was a factor of 5–10 smaller than the H2O self-relaxation rate constant.