COLLISION EFFECTS IN THE MULTI-PHOTON DISSOCIATION OF SF6

Measurements of multiphoton dissociation (MPD) of 32SF6 by irradiation with a single TEA CO2 laser pulse as a function of gas pressure are reported. Superexcitation conditions and pulses of different lengths were used to investigate collision effects on the MPD of SF6. In addition the energy of the pulses transmitted through the absorption cell was measured to distinguish between optical absorption and collision effects on the MPD. The results using laser pulses of 8 J with a duration of 150 ns show that at low gas pressures there is an almost constant MPD yield where 15% of the molecules is dissociated in a single pulse, whereas at pressures higher than 0.1 Torr a strong decrease of the MPD yield is found. The transmitted pulse energy in this case follows the MPD behavior as a function of pressure. The results with the stronger laser pulses of 30 J and duration of ≈ 1 μs show a pressure dependence of the MPD similar to that obtained with the weaker pulses, but with 100% yield at the low gas pressures. The transmitted pulse energy, however, was found to be almost constant at pressures up to 0.3 Torr. The present results indicate that collisions with photofragments provide the most likely channel for the observed decrease of the MPD yield versus pressure. © 1979.