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Ab initio molecular orbital study on structures and energetics of CH 3 O − (H 2 O) n and CH 3 S − (H 2 O) n in gas phase
Author(s) -
Masamura Masao,
Ikuta Shigeru
Publication year - 1999
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/(sici)1096-987x(199908)20:11<1138::aid-jcc4>3.0.co;2-d
Subject(s) - ab initio , bond length , chemistry , molecule , hydrogen bond , moiety , ab initio quantum chemistry methods , phase (matter) , gas phase , molecular geometry , computational chemistry , crystallography , stereochemistry , organic chemistry
The purpose of this article was to calculate the structures and energetics of CH 3 O − (H 2 O) n and CH 3 S − (H 2 O) n in the gas phase; the maximum number of water molecules that can directly interact with the O of CH 3 O − ; and when n is larger, we asked how the CH 3 O − and CH 3 S − moiety of CH 3 O − (H 2 O) n and CH 3 S − (H 2 O) n changes and how we can reproduce experimental Δ H 0 n −1, n . Using the ab initio closed‐shell self‐consistent field method with the energy gradient technique, we carried out full geometry optimizations with the MP2/aug‐cc‐pVDZ for CH 3 O − (H 2 O) n ( n =0, 1, 2, 3) and the MP2/6–31+G(d,p) (for n =5, 6). The structures of CH 3 S − (H 2 O) n ( n =0, 1, 2, 3) were fully optimized using MP2/6–31++G(2d,2p). It is predicted that the CH 3 O − (H 2 O) 6 does not exist. We also performed vibrational analysis for all clusters [except CH 3 O − (H 2 O) 6 ] at the optimized structures to confirm that all vibrational frequencies are real. Those clusters have all real vibrational frequencies and correspond to equilibrium structures. The results show that the above maximum number of water molecules for CH 3 O − is five in the gas phase. For CH 3 O − (H 2 O) n , when n becomes larger, the C—O bond length becomes longer, the C—H bond lengths become smaller, the HCO bond angles become smaller, the charge on the hydrogen of CH 3 becomes more positive, and these values of CH 3 O − (H 2 O) n approach the corresponding values of CH 3 OH with the n increment. The C—O bond length of CH 3 O − (H 2 O) 3 is longer than the C—O bond length of CH 3 O − in the gas phase by 0.044 Å at the MP2/aug‐cc‐pVDZ level of theory. The structure of the CH 3 S − moiety in CH 3 S − (H 2 O) n does not change with the n increment. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1138–1144, 1999