Ab initio MO study on the structures of OH- (H2O)n in the gas phase

The purpose of this article is to show that (i) the OH- ion binds strongly to up to five water molecules in the gas phase, and (ii) the OH- (H2O)(n) has a C-n symmetry in the gas phase. For this purpose, the structures of OH- (H2O)(n) (n = 0-6) were fully optimized with MP2/6-31 + + G(d), and those of OH- (H2O)(n-1)(H2O) (n = 4,5) were partially optimized with MP2/6-31 + + G(d), and the energy differences between OH- (H2O)(5) and OH- (H2O)(4)(H2O)were calculated by MP3/6-31 + + G(d), MP4/6-31 + + G(d), MP2/6-31 + G(2d, 2p), MP2/aug-cc-pVDZ and MP2/6-311 + G(3df, 2p) at the MP2/6-31 + + G(d) optimized structures. We also performed a vibrational analysis for OH- (H2O)(n) (n = 0-5) using MP2/6-31 + + G(d) at the optimized structures to confirm that all vibrational frequencies are real. These calculations show that the OH- ion binds strongly to up to five water molecules in the gas phase, and that OH- (H2O)(n) has a C-n symmetry in the gas phase. (C) 2000 Elsevier Science B.V. All rights reserved.