Towards an understanding of the predissociation excitation spectrum of H₃⁺

Abstract

A high angular momentum H⁺/H₂ complex model is used to assess the factors responsible for the recently reported vibrational predissociation spectrum of H₃ ⁺. The resulting eigenvalue spectrum for J = 30–45 shows a mean state density of one state per 30 cm^-1 for each parity block with a given J value. Typically 10 of the these states, closely grouped in energy, have lifetimes in the experimentally detected range. Weak laser field spectra, induced by the dipole moment of the H⁺/H₂ complex, show features between 700 and 900 cm^-1 which are assignable to pure orbital excitation, Δl = 1, transitions. Transitions in the higher frequency experimental region, 872–1094 cm^-1, can be accounted for only if the spectrum is assumed to be saturated, in which case the observation of 27 000 experimental lines is readily accommodated by the theory. However there are no calculated spectral features to correlate with the peaks in the low resolution experimental spectrum. Avenues for future theoretical progress are discussed.