The effect of deuteration on the multiphoton dissociation of benzene chromium tricarbonyl

We have measured one color multiphoton dissociation ionization (MPD/MPI) spectra for h₆-benzene chromium tricarbonyl (h₆-BCT) and d₆-benzene chromium tricarbonyl (d₆-BCT). These spectra reveal that the vibrational properties of the ligands determine the distribution of metal atom states formed by MPD of organometallic molecules. Pressure studies demonstrate that the observed effects manifest isolated molecule dynamics and that excited triplet states are probably not involved in those dynamics. Laser power dependence studies show that the observed branching between MPD production of ground state chromium atoms vs excited state atoms is a function of multiphoton excitation rate. It seems likely that photodissociation on potential surfaces corresponding to excited electronic states can occur before intramolecular energy redistribution is complete. Two mechanisms consistent with our results are suggested. One is very unique for MPD/MPI experiments in that ladder crossing based on dissociation is not the source of the branching between observed products.