Infrared photodissociation of a water molecule from a flexible molecule-H2O complex: Rates and conformational product yields following XH stretch excitation

Infrared-ultraviolet hole-burning and hole-filling spectroscopies have been used to study IR-induced dissociation of the tryptamine∙H2O and tryptamine∙D2O complexes. Upon complexation of a single water molecule, the seven conformational isomers of tryptamine collapse to a single structure that retains the same ethylamine side chain conformation present in the most highly populated conformer of tryptamine monomer. Infrared excitation of the tryptamine∙H2O complex was carried out using a series of infrared absorptions spanning the range of 2470–3715cm−1. The authors have determined the conformational product yield over this range and the dissociation rate near threshold, where it is slow enough to be measured by our methods. The observed threshold for dissociation occurred at 2872cm−1 in tryptamine∙H2O and at 2869cm−1 in tryptamine∙D2O, with no dissociation occurring on the time scale of the experiment (∼2μs) at 2745cm−1. The dissociation time constants varied from ∼200ns for the 2869cm−1 band of tryptamine...