Effect of rotational relaxation on the yield of the multiphoton dissociation of CF₃Cl and CF₃Br under TEA-CO₂ laser pulses

The yield of the multiphoton dissociation of CF₃Cl and CF₃Br induced by TEA-CO₂ laser pulses has been studied in the pressure range between 0.25 and 8 Torr, the laser wavelength being chosen so as to excite preferentially the minor isotopic components¹³CF₃Cl and¹³CF₃Br. For both compounds the dissociation probability is found either to increase almost linearly or to decrease monotonously with gas pressure, according as the laser beam is focused or unfocused, respectively. This behaviour is explained by rotational relaxation effects, and a value of 22ns·Torr for the rotational self-relaxation time of CF₃Cl is obtained.