Infrared dissociation of ammonia clusters

Dissociation spectra of NH3 clusters have been recorded using a cw CO2 laser. For the dimer two absorption bands have been found at 979 and 1004 cm-1, which originate from the excitation of two non-equivalent NH3 molecules. A tunneling motion is held responsible for the observed structure on one of these bands. The symmetry group of the NH3 dimer is presented considering the tunneling motion solely. Heavier NH3 clusters dissociate at frequencies between 1020 and 1100 cm-1. The dissociation spectrum of the SiH4-NH3 complex shows one peak centered at 972.3 cm-1.