A NEW INTERMOLECULAR POTENTIAL FOR HYDRAZINE CLUSTERS - STRUCTURES AND SPECTRA

The structures of small hydrazine clusters from the dimer to the hexam er have been calculated using a standard site-site intermolecular pote ntial and a newly developed systematic approach which is essentially b ased on monomer properties. Aside from the repulsive and the attractiv e dispersion and induction interaction special care is taken for the d etermination of the electrostatic interaction which is represented by a distributed multipole expansion and a penetration correction. Based on these potentials the vibrational spectra of the N-N stretching and the asymmetric NH2 wagging mode are calculated using degenerate pertur bation theory. While the small shifts of the N-N stretching mode are f airly well reproduced by both potential models, large differences are predicted for the asymmetric NH2 wagging mode. Here, redshifts of -30 cm(-1) are calculated for the standard and blueshifts of 100 cm(-1) ar e obtained for the systematic potential in agreement with experiment. The analysis shows that the reason for this behavior is the careful tr eatment of the electrostatic term in this model. (C) 1997 American Ins titute of Physics.