Roaming dynamics in formaldehyde-d2 dissociation.

State-resolved photodissociation dynamics of formaldehyde-d(2), i.e., D(2)CO, at energies slightly above the deuterium atom elimination channel have been studied both experimentally and theoretically. The results showed a clear bimodal distribution of energy into molecular photofragments. Substantial translational excitation of products at high rotational levels of CO was observed together with the D(2) cofragment in moderately excited vibrational levels, whereas rather small translational energy release of CO in low rotational levels was matched by a large degree of vibrational excitation in the D(2) molecule. An analogous distribution of energy in two distinct channels has been recently observed under similar conditions in H(2)CO photolysis and attributed to two different dissociation pathways, namely, a pathway via the conventional transition state geometry and the previously unobserved pathway, deemed "roaming". Our experimental and theoretical data indicated that the same two dissociation pathways were responsible for the bimodal energy distribution into the molecular fragments resulting from the photolysis of D(2)CO. Energy partitioning into molecular products was compared between photolysis of H(2)CO and D(2)CO at energies slightly above the H/D atom abstraction threshold.