Molecular dissociation of SF 6 by ultra-short CO 2 laser pulses

We have measured the absolute dissociation probability of SF ₆ gas irradiated by CO ₂ laser pulses varying in duration from 0.5 nsec to 100 nsec. We find a threshold for dissociation of ≃ 1.4 J/ cm², independent of pulse duration. For fixed energy density, the dissociation probability increases as the pulse duration decreases, but not nearly to the degree expected from theory. We have also determined the dissociation probability in the ν₂ + ν₆ combination band and find it to be 10 ³ times less than in the ν ₃ band, in contradiction to some conclusions recently reported by Ambartzumian et al. The dissociation mechanism takes place without collisions, and if collisions occur, they tend to be detrimental to the dissociation rate.