Structures of protonated hydrogen sulfide clusters, H⁺(H₂S)_n, highlighting the nature of sulfur-centered...

Unique intermolecular structures of protonated hydrogen sulfide clusters, H⁺(H₂S)_n, 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⁺(H₂O)_n, in spite of the common hydrogen bond coordination ability between hydrogen sulfide and water. Protonated hydrogen sulfide clusters have the Eigen type ion core, H₃S⁺, 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⁺(H₂S)_n is discussed.