Anharmonic force constants of helical molecules

Central to our anharmonic potential-effective charge method of computing relative Raman intensities of large helical molecules, such as DNA, are the anharmonic force constants of such molecules. We have thus been led to derive explicit expressions of them and to study their properties. These properties prove to be indispensable in carrying out the computational steps leading to the final Raman intensity expressions for helical molecules. A general expression of cubic force constants of a helical molecule is presented and its properties discussed. Explicit expressions are listed for the cases of stretch and anglebend contributions. Other uses of the anharmonic force constants are also discussed. (C) 1995 John Wiley & Sons, Inc.