Intermolecular Vibration Coupling between Libration of Water and ν2-SOH for Clusters HSO4-(H2O)n

The hydrated bisulfate ion clusters (HSO4-(H2O)(n), n = 1-10) were optimized at the M06/6-311++G(d,p) level. The factors affecting v,SOH of the clusters involved vibration coupling between nu(2)-SOH and the water wagging libration mode (W-H2O) and hydrogen bonding effect. In order to understand the vibration coupling between W-H2O and nu(2)-SOH for the bisulfate clusters, D2O instead of H2O and Se instead of S were used to estimate the uncoupling frequency of nu(2)-SOH and W-H2O, respectively. For HSO4-center dot H2O-I, the uncoupling frequencies of nu(2)-SOH and W-H2O were obtained at 752.0 and 753.4 cm(-1). After coupling, the frequencies appeared at 782.2 and 732.6 cm(-1). H2S and NH4+ instead of D2O in HSO4-center dot D2O-II were compared to analyze the effect of hydrogen bond. The sequence of hydrogen bond strength was found to be HSO4-center dot H2S-II < HSO4-center dot D2O-II < HSO4-center dot NH4+-II with the respective nu(2)-SOH at 736.7, 740.5, and 802.2 cm(-1) increasing in the same order. In HSO4-center dot(H2O)(n), coupling appeared when n was from 1 to 8. For HSO4-center dot(D2O)(n), no coupling between nu(2)-SOH and D2O librations made it possible to understand the hydrogen bonding effect on the nu(2)-SOH. The frequencies of nu(2)-SOH for clusters HSO4-(D2O) almost linearly decreased from 752.0 to 854.6 cm(-1) with n from 1 to 10.