Modelling and calculation of dipole moment functions for XH bonds

Two studies of aspects of modelling dipole moment functions of XH bonds in small molecules for use in calculating overtone intensities have been under taken. The first study deals with the fitting of ab initio calculations of the dipole moment at discrete points to a functional form. The two methods that are compared are the use of least-squares regression and the use of in terpolating polynomials. The interpolating polynomial method is deemed supe rior due to its greater efficiency in terms of the number of points necessa ry to obtain reasonable results. The second study attempts to explain the i ndifference of calculated overtone intensities to the inclusion of electron correlation in the ab initio calculation of the dipole moment function. It is found that in most cases the influence of electron correlation can be m odelled as a function with a very small matrix element, which results in a very small contribution to the overtone intensity.