VIBRATIONAL PREDISSOCIATION SPECTRA OF SIZE-SELECTED HYDRAZINE CLUSTERS - EXPERIMENT AND CALCULATIONS

Vibrational predissociation spectra of hydrazine (N2H4)(n) clusters ha ve been measured from the dimer to the tetramer using a linetunable, i sotopically substituted CO2-laser in order to fill the frequency gap b etween 990 and 1010 cm(-1). The clusters are size selected in a scatte ring experiment with helium atoms. The large blue shifts of the asymme tric NH2 wag mode at 937 cm(-1) are completely interpreted by calculat ions based on a recently determined systematic model potential. The gr oss shifts of 60 cm(-1) for the dimer, 80 cm(-1) for the trimer, and 1 10 cm(-1) for the larger clusters are explained by the different struc tures: Cyclic arrangements with two hydrogen bonds per molecule for th e dimer, rings with one hydrogen bond per molecule for the trimer, and three-dimensional structures for the larger ones. The peaks in the sp ectra are caused by characteristic vibrations to which more than one i somer contributes. (C) 1997 American Institute of Physics.