Transient vibration and product formation of photoexcited CS2 measured by time-resolved x-ray scattering

We have observed details of the internal motion and dissociation channels in photoexcited carbon disulfide (CS2) using time-resolved x-ray scattering (TRXS). Photoexcitation of gas-phase CS2 with a 200 nm laser pulse launches oscillatory bending and stretching motion, leading to dissociation of atomic sulfur in under a picosecond. During the first 300 fs following excitation, we observe significant changes in the vibrational frequency as well as some dissociation of the C-S bond, leading to atomic sulfur in the both D-1 and P-3 states. Beyond 1400 fs, the dissociation is consistent with primarily P-3 atomic sulfur dissociation. This channel-resolved measurement of the dissociation time is based on our analysis of the time-windowed dissociation radial velocity distribution, which is measured using the temporal Fourier transform of the TRXS data aided by a Hough transform that extracts the slopes of linear features in an image. The relative strength of the two dissociation channels reflects both their branching ratio and differences in the spread of their dissociation times. Measuring the time-resolved dissociation radial velocity distribution aids the resolution of discrepancies between models for dissociation proposed by prior photoelectron spectroscopy work. Published under an exclusive license by AIP Publishing.

Automated summary

We used time-resolved x-ray scattering to investigate internal motion and dissociation channels in photoexcited carbon disulfide. The results showed that photoexcitation led to oscillatory bending and stretching motion, followed by dissociation of atomic sulfur. The dissociation process exhibited different behaviors at different time intervals, with significant changes in vibrational frequency and partial dissociation of the C-S bond observed within the first 300 fs. The resolved dissociation time provided insights into the branching ratio and differences between the two dissociation channels.