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The presence of a two-center three-electron (2c–3e) bonded (hemi-bonded) ion core in the (H2S)n + cluster is revealed by infrared spectroscopy combined with ab initio calculations. The stability of the hemi-bonded ion core to solvation is also proved.

IR spectroscopy of [benzene-(H2S)n]+ (n = 1–4) elucidates the change of the positive charge accommodation motif from the S∴π hemibond to the S∴S hemibond.

The three-electron two-center (3e-2c) bond plays an important role in structures and electron communication in biological systems involving cationic sulfur compounds. Although the nature of 3e-2c bonds and their theoretical formalism have attracted great interest, direct spectral identifications of 3e-2c-bound molecules are scarce. We observed the infrared spectra of the weakly 3e-2c-bound CHS∴S(H)CH and the strongly 3e-2c-bound (CHSH) in a supersonic jet using infrared (IR) dissociation with vacuum-ultraviolet photoionization and time-of-flight detection. Protonation of CHS∴S(H)CH to form [CH(H)S∴S(H)CH] significantly enhances the 3e-2c bond, characterized by a large red shift of the SH-stretching band with enhanced IR intensity, shortening of the calculated S-S distance from 3.00 to 2.86 Å, and a dissociation energy increased from ∼23 to 162 kJ mol.

The microsolvation effect on the S∴S hemibond is studied by IR spectroscopy of model clusters of H2S, and the results are compared with the microsolvation of protonated H2S clusters.

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Unique intermolecular structures of protonated hydrogen sulfide clusters, H(HS), are revealed by infrared spectroscopy and ab initio calculations. The identified intermolecular structures are significantly different from those of the corresponding protonated water clusters, H(HO), in spite of the common hydrogen bond coordination ability between hydrogen sulfide and water. Protonated hydrogen sulfide clusters have the Eigen type ion core, HS, in the size range of n = 3-9. After the first hydrogen bonded shell formation is completed at n = 4, further solvation prefers a new shell bound by the charge-dipole interaction rather than the second hydrogen bonded shell. Thus, closely solvated structures, in which 7 molecules, at maximum, directly interact with the Eigen type ion core, are formed. The beginning of the second hydrogen bonded shell is found at n = 9. Competition among intermolecular interactions in H(HS) is discussed.

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