|
435. CDIST: Centrifugal Distortion Constants for Diatomic
Molecules
by Jeremy M. Hutson, Physical Chemistry Laboratory, Oxford University, Oxford OX1 3QZ, England CDIST calculates energy levels, rotational constants, and centrifugal distortion constants Dv, Hv, Lv and Mv from a numerically specified potential curve. The method used is that of Hutson (1981), which is a reformulation of the perturbation theory scheme of Albritton et al. (1973). The present method differs from the earlier perturbation theory method in that it does not rely on convergence of a basis set expansion and includes the effects of continuum levels exactly, so that it is valid for all vibrational levels, even near dissociation. The program is written to allow the user to supply his own subroutine for generating the potential curve. However, a subroutine CDPOT is supplied to generate curves suitable for most applications. CDPOT has options for various analytical functions (Morse, Lennard-Jones, etc.) or can take a pointwise potential from the data file. In the latter case, the supplied points are interpolated using a product of a Morse potential and a piecewise cubic polynomial. This method minimizes the number of points that must be supplied to give an accurate representation of the potential. Options are also provided to extrapolate the pointwise potential to longer and shorter distances, using appropriate functional forms. CDIST has two different ways of choosing the vibrational levels for which constants are to be calculated. It can read in estimates of the level energies (in which case the program will converge to the nearest level) or it can find the vibrational levels for itself. This latter option is quite time consuming, so that it is preferable to supply estimates of the level energies if they are available. FORTRAN IV Lines of Code: 1200 |