The Vibrational Dynamics of Hydrogen Bonded Molecular Complexes at the State-to-State Level

Abstract

In recent years our understanding of the vibrational predissociation dynamics of weakly bound molecular complexes has improved greatly owing to both the experimental and theoretical advances that have been made in this area. We are now in the very fortunate position where both theory and experiment often can be brought to bare on the same system. The developments made in our laboratory involve the use of the opto-thermal detection technique to measure the infrared spectra and state-to-state dissociation rates for a number of these complexes. In the present report we examine the affects of molecular orientation on the rate of vibrational relaxation. This is done by measuring the predissociation lifetimes associated with several vibrational modes of different isomeric forms of a binary complex. The vibrational relaxation rates are found to be highly anisotropic and several interesting correlations can be made between this data and the collisional relaxation results already available in the literature. In addition to the relaxation data obtained from measuring lifetimes, one also would like to obtain information on the disposal of excess energy in the fragments which result from vibrational predissociation of the parent complex. This clearly involves the measurement of state-to-state dissociation rates for these complexes. Results of this type have recently been obtained from measurements of the angular distributions of the photofragments and will be discussed for systems such as HF and HCN dimers. In favorable cases data of this type can provide relative state-to-state rates which can be used as sensitive tests of the emerging theoretical methods. Comparisons with simple statistical theories show that the dissociation dynamics associated with these systems is highly non-statistical.