Photodissociation dynamics of ethanethiol in clusters: complementary information from velocity map imaging, mass spectrometry and calculations

We investigate the solvent effects on photodissociation dynamics of the S-H bond in ethanethiol CH3CH2SH (EtSH). The H fragment images are recorded by velocity map imaging (VMI) at 243 nm in various expansion regimes ranging from isolated molecules to clusters of different sizes and compositions. The VMI experiment is accompanied by electron ionization mass spectrometry using a reflectron time-of-flight mass spectrometer (RTOFMS). The experimental data are interpreted using ab initio calculations. The direct S-H bond fission results in a peak of fast fragments at Ekin(H) ≈ 1.25 eV with a partly resolved structure corresponding to vibrational levels of the CH3CH2S cofragment. Clusters of different nature ranging from dimers to large (EtSH)N, N ≥ 10, clusters and to ethanethiol clusters embedded in larger argon "snowballs" are investigated. In the clusters a sharp peak of near-zero kinetic energy fragments occurs due to the caging. The dynamics of the fragment caging is pictured theoretically, using multi-reference ab initio theory for the ethanethiol dimer. The larger cluster character is revealed by the simultaneous analysis of the VMI and RTOFMS experiments; none of these tools alone can provide the complete picture.