Non-Adiabatic Interactions in the Spectra of Small Polyatomic Molecules: the a State of Ammonia and the Electronic Spectrum of Methinophosphide.

Microwave-detected, microwave optical double resonance spectra were recorded of the predissociative NH _3, NH_2, NHD _2, and ND_3 A states. With this approach, both vibrational and rotational transitions were resolved and homogeneous transition linewidths measured. From the transition frequencies, we determined the equilibrium structure and experimentally estimated the harmonic force field for the A state. From the homogeneous linewidths, the vibrational and rotational contributions to the A state predissociation were determined. Predissociation from the lowest two levels occurred by tunneling through a barrier of 2100 cm^{-1} while predissociation from levels containing more than two quanta in nu_2 occurred through a Fermi coupling of nu_2 with the dissociation coordinate. Due to the differences in zero point energy, the rotational predissociation mechanisms for NH_3 and ND_3 differed; rotational contributions for NH _3 were Coriolis dominated while for ND _3 rotational contributions were predominantly centrifugal. Fluorescence excitation spectra were recorded of HCP and DCP seeded in a supersonic jet from the start of the strong singlet absorption to the ground state dissociation threshold where we observed a sharp breakoff in fluorescence intensity. We observed nearly five times the number of bands previous observed through absorption. Many of the these bands were assigned to higher lying members of the A state enabling us to determine an empirical potential energy surface for this state. Over twenty bands were assigned to the higher lying C state, which was shown to be the lower shelf of a Renner-Teller split ^1 Delta state. The majority of the remaining bands remain unassigned. To aid in the assignment of these bands, microwave induced fluorescence depletion and lifetimes were recorded.