5314027786

POSTER SESSION, H5

CALCULATION OF INTERMOLECULAR MOTION AND ELEC-TROOPTIC PARAMETERS OF THE HCN...HF DIMER

M. O. BULANIN, V. P. BULYCHEY and K. G. TOKHADZE, 1

Institute oj Physics, St. Petersburg State University, Petcrhof, St. Petersburg, 198904 Russia.

In this calculation we use a semiempirical 4D potential composed of electrostatic, disper-sion, and repulsion interactions between the sites in two inonomers, which correctly repro-duces the experimental well depth and equilibrium separation. An effective 4D Hamiltonian describes the translational and librational motions of the monomers and their relative rotation in the body-flxed frame. The wavc functions are expanded in products of Morse-like radial functions and eigenfunctions of the sum of angular momenta of the monomers. The number of basis functions is sufficicntly large to ascribe possible inaccuracy of results to the inadequacy of the potential only. The nodal structure of the wave functions and their predominant localization in a particular region are used to characterize the naturę of levels and transitions. Weights of the basis functions in different Solutions, avcrage values of geometrie parameters, and their variances are also considered. In generał, motions in-volving different degrees of freedom are found to be strongly coupled. Frequencies of the intermolecular stretching modę, librations of HCN and HF subunits, and sparing between the lowest opposite-parity levels are 150, 178, 559. and 286 cm'¹, respectively. The first and third values are in good agrcement with experimental data, whereas the second is too large. A dipole moment function containing interaction- induced contri but ions are employed to evaluate various elcctrooptic parameters. Calculated values of the transition dipole moments and frequencies allow us to reconstruct the profile of the “shear" modę band at about 550 cm"¹. The contour obtained is very similar to that experiinentally observed, a value of the band strength making up 56% of the experimental value. The strength of the intramolecular HF modę is found to inerease on complexation by a factor of 2.1. The vibrationally averaged value of the dipole moment of the complex is larger by 0.61 D than the vector sum of monomer moments.