Isotope effects on rapid vibrational deactivation of laser-excited nitrous oxide by sulfur hexafluoride

Single exponential 4.5 micron fluorescence decay times are observed from samples containing SF6 and 14N14NO or 14N15NO. The nitrous oxides are excited directly to the 0001 level by a Q-switch CO2 laser. Decay times are dominated by the partial pressure of SF6 in the sample. At room temperature the rate constant for 14N14NO--SF6 is 1200 ms-1 torr(SF6)-1, and for 14N15NO--SF6 is 200 ms-1 torr(SF6)-1. The cross sections for each isotopically differentiated N2O decreases as the temperature increases. The excited N2O level for 14N15NO is ∼50 cm-1 lower than that for 14N14NO. This increase in the energy defect can account for the decrease in efficiency by long range coulombic forces