Electronic and Infrared Spectroscopy of Benzene-(HS) ( = 1 and 2): The Prototype of the SH-π Interaction.

Benzene-(HS) ( = 1 and 2) clusters are the simplest prototype exemplifying the SH-π interaction. Electronic and infrared spectroscopies were applied to the benzene-(HS) clusters under the molecular beam condition. The S-S electronic spectrum was observed by one-color resonant two-photon ionization combined with mass spectrometry. Ionization depletion infrared spectra were also observed in the CH and SH stretch regions. The isomer-selective infrared spectra demonstrated that at least two isomers of = 1 coexist under the present beam condition, and both of them have the SH-π bound structures. One isomer showed a red-shift in the S-S electronic transition relative to that of bare benzene, while the electronic transition of another isomer was slightly blue-shifted. For = 2, we confirmed a structure, in which hydrogen-bonded HS dimer is located on top of the aromatic ring.