New insights on the photodissociation of N-methylpyrrole: the role of stereoelectronic effects.

We investigated the reaction dynamics of N-methylpyrrole (NMP) along the N-CH3 coordinate, upon excitation energies below 6.4 eV. Ours and previous experiments show clearly the existence of different reaction channels leading to slow and fast fragment production whose relative efficiency fluctuates with the changes in the excitation energy. Thanks to our modeling based on the differences of the NMP molecular orbitals (MOs) with respect to those of pyrrole we are able to show the existence of two low lying dissociative pi sigma(N-CH3)* states. Those states originate from the degeneracy removal in the pi MOs owing to their interaction with the sigma(CH) MO of the methyl group. This evidence and the calculated potential energy surfaces for dissociation along the N-CH3 coordinate provide the correct framework for the interpretation of the details in the NMP photodissociation dynamics.