Gas-Phase Infrared Spectroscopic Investigation of S-H···S Hydrogen Bonds in (H₂S)_n (n = 2-6) Clusters

While O-H···O hydrogen (H) bonds have been vigorously investigated, gas-phase studies of S-H···S H bonds remain very limited, especially in cases where multiple H bonds form a network. In this study, we investigate S-H···S H bonds in hydrogen sulfide clusters, (H₂S)_n (n = 2-6), in the gas phase with size-selective infrared spectroscopy based on vacuum ultraviolet photoionization detection. For clusters with n ≥ 3, the H-bonded SH stretching frequency remains nearly constant irrespective of the cluster size, a trend that contrasts with previously reported observations from the Ar matrix isolation spectra. (H₂S)_n (n > 3) clusters prefer to form dense three-dimensional H-bond networks to enhance the contribution of dispersion forces. These behaviors of (H₂S)_n significantly differ from those of the OH H-bond networks in (H₂O)_n. This study reveals that S-H···S H-bond networks in (H₂S)_n are characterized by weak cooperativity and a substantial contribution from dispersion forces.