State Distributions of HCO and CH3 Products in the Ultraviolet Photodissociation of N , N -Dimethylformamide

Abstract

We examined the effect of nonplanarization of the amide framework on the photodissociation dynamics of N,N-dimethylformamide (DMF, (CH3)2N(CO)H) at 213 nm. The final state distributions of the photodissociation products in the N–CO and N–CH3 bond dissociation pathways were measured using laser-induced fluorescence and resonance-enhanced multiphoton ionization spectroscopy. The formation of highly vibrationally excited HCO products over the dissociation threshold was confirmed by detecting the H and CO products of the sequential dissociation. The vibrational and rotational excitation of HCO indicated the nonplanar deformation in the 21A′(ππ*) excited state of DMF. The reaction route through the fast internal conversion (21A′(ππ*) → 11A″(nπ*)) facilitated at the nonplanar structure was demonstrated with theoretical calculations. In contrast, the energy partitioning of the N–CH3 bond dissociation pathway was found to be statistically distributed. We attributed the relatively slow mechanism to an energy barrier on the dissociation route based on the theoretical potential energy surface of 21A′(ππ*).