Photoionization and photofragmentation of SF6 in helium nanodroplets.

The photoionization of He droplets doped with SF6 was investigated using tunable vacuum ultraviolet (VUV) synchrotron radiation from the Advanced Light Source (ALS). The resulting ionization and photofragmentation dynamics were characterized using time-of-flight mass spectrometry combined with photofragment and photoelectron imaging. Results are compared to those of gas-phase SF6 molecules. We find dissociative photoionization to SF5+ to be the dominant channel, in agreement with previous results. Key new findings are that (a) the photoelectron spectrum of the SF6 in the droplet is similar but not identical to that of the gas-phase species, (b) the SF5+ photofragment velocity distribution is considerably slower upon droplet photoionization, and (c) fragmentation to SF4+ and SF3+ is much less than in the photoionization of bare SF6. From these measurements we obtain new insights into the mechanism of SF6 photoionization within the droplet and the cooling of the hot photofragment ions produced by dissociative photoionization.