Vibrational relaxation studies in CO2, N2O, and H2O using a tunable infrared laser

Laser-excited vibrational fluorescence experiments on the H2O asymmetric stretch, and on the CO2 and N2O combination levels are carried out with a tunable infrared laser. Rate constants near gas kinetic are obtained for CO2 and N2O and assigned to the near resonant V approaches V transfer of an asymmetric stretching quantum. Stimulated emission from the CO2 combination level at 4.3 micron is observed during laser excitation at 2.7 micron. Energy transfer experiments are conducted on water vapor and isotopically labeled H2O18. Water vibrationally relaxes with anomalously large rates. Energy transfer from the bending vibration to rotation and translation requires about 3.3 collisions. Energy is transferred from the bending overtone to the bending fundamental in only 2.3 collisions. Energy is transferred from the asymmetric stretch to the bend in 8 collisions. Argon is 200 times less effective than water, itself, as a collision partner. Measurements are made by direct excitation of single rotational levels of the asymmetric stretching vibration with an optical parametric oscillator. Infrared fluorescence is detected from the stretching and bending regions.