A new intermolecular potential for hydrazine clusters: Structures and spectra

The structures of small hydrazine clusters from the dimer to the hexamer have been calculated using a standard site-site intermolecular potential and a newly developed systematic approach which is essentially based on monomer properties. Aside from the repulsive and the attractive dispersion and induction interaction special care is taken for the determination 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 perturbation theory. While the small shifts of the N-N stretching mode are fairly 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) are obtained for the systematic potential in agreement with experiment. The analysis shows that the reason for this behavior is the careful treatment of the electrostatic term in this model. (C) 1997 American Institute of Physics.