Vibrational predissociation spectra of size selected hydrazine clusters: Experiment and calculations

Vibrational predissociation spectra of hydrazine (N2H2)n clusters have been measured from the dimer to the tetramer using a linetunable, isotopically substituted CO2-laser in order to fill the frequency gap between 990 and 1010 cm−1. The clusters are size selected in a scattering experiment with helium atoms. The large blue shifts of the asymmetric NH2 wag mode at 937 cm−1 are completely interpreted by calculations based on a recently determined systematic model potential. The gross shifts of 60 cm−1 for the dimer, 80 cm−1 for the trimer, and 110 cm−1 for the larger clusters are explained by the different structures: Cyclic arrangements with two hydrogen bonds per molecule for the dimer, rings with one hydrogen bond per molecule for the trimer, and three-dimensional structures for the larger ones. The peaks in the spectra are caused by characteristic vibrations to which more than one isomer contributes.