Hydrogen-bonded complexes involving HF and HCl: the effects of electron correlation and anharmonicity |
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Authors: | R D Amos J F Gaw N C Handy E D Simandiras K Somasundram |
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Institution: | (1) University Chemical Laboratory, Lensfield Road, CB2 1EW Cambridge, UK |
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Abstract: | Calculations on the hydrogen-bonded complexes HCN HF, H2O HF, ClCN HCl and (CH3)2O HCl are reported. SCF harmonic values for the HF and HCl frequency shifts are in considerable disagreement with experiment, by as much as 100 cm–1. Calculations at the MP2 (harmonic) level yield improved agreement with experiment, reducing discrepancies to the order of 10 cm–1. We have also calculated all the cubic and quartic force constants for HCN HF at the SCF level, so that the anharmonic constants, x
rs
can be evaluated. Although x
11 (v
1=H-F stretch) is large and negative, it is more than compensated by a positive x
16 (v
6=N H-F bend), so that the anharmonic correction to v
1 is small and positive. The validity of these anharmonistudies is examined. |
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Keywords: | Hydrogen bonds Frequency shifts Anharmonicity |
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