Intermolecular vibration coupling between libration of water and ν2-SOH for Clusters HSO4(-)(H2O)n

The hydrated bisulfate ion clusters (HSO(4)(-)(H(2)O)(n), n = 1-10) were optimized at the M06/6-311++G(d,p) level. The factors affecting ν(2)-SOH of the clusters involved vibration coupling between ν(2)-SOH and the water wagging libration mode (W-H(2)O) and hydrogen bonding effect. In order to understand the vibration coupling between W-H(2)O and ν(2)-SOH for the bisulfate clusters, D(2)O instead of H(2)O and Se instead of S were used to estimate the uncoupling frequency of ν(2)-SOH and W-H(2)O, respectively. For HSO(4)(-)·H(2)O-I, the uncoupling frequencies of ν(2)-SOH and W-H(2)O were obtained at 752.0 and 753.4 cm(-1). After coupling, the frequencies appeared at 782.2 and 732.6 cm(-1). H(2)S and NH(4)(+) instead of D(2)O in HSO(4)(-)·D(2)O-II were compared to analyze the effect of hydrogen bond. The sequence of hydrogen bond strength was found to be HSO(4)(-)·H(2)S-II < HSO(4)(-)·D(2)O-II < HSO(4)(-)·NH(4)(+)-II with the respective ν(2)-SOH at 736.7, 740.5, and 802.2 cm(-1) increasing in the same order. In HSO(4)(-)·(H(2)O)(n), coupling appeared when n was from 1 to 8. For HSO(4)(-)·(D(2)O)(n), no coupling between ν(2)-SOH and D(2)O librations made it possible to understand the hydrogen bonding effect on the ν(2)-SOH. The frequencies of ν(2)-SOH for clusters HSO(4)(-)(D(2)O)(n) almost linearly decreased from 752.0 to 854.6 cm(-1) with n from 1 to 10.