Rotational state distributions of H2 and CO following the photofragmentation of formaldehyde

The rotational state distributions of H2 and CO following the photo-fragmentation of formaldehyde at wavelengths of about ∼29 500 cm−1 are analyzed using a simple model. The ingredients of the model are an ab initio potential energy surface in the excit channel and the known geometry of the H2CO→H2+CO transition state. Both the ortho H2 and the CO distributions agree very well with recent measurements. While the CO rotational distribution is directly determined by the excit channel dynamics (i.e., the potential energy surface) the H2 distribution is exclusively determined by the Franck–Condon principle (i.e., the transition state geometry). CO and H2 rotations are almost completely uncorrelated. All results are easily understandable in terms of the calculated potential energy surface.