Photodissociation dynamics of formyl fluoride via the triplet state surface: a direct ab-initio dynamics study

Abstract

Direct ab-initio dynamics calculations have been applied to the photodissociation of the HFCO molecule on the potential energy surface at the triplet state in order to elucidate its reaction mechanism and to determine the energy partitioning in the products. Two reaction channels, HFCO(T₁)→H(²S)+FCO(X²A′) and HFCO(T₁)→F(²P)+HCO(X²A′) (denoted as channels 1 and 2, respectively) were considered as decay processes of HFCO(T₁). Ab-initio molecular orbital calculations showed that the activation barrier for channel 1 is significantly lower than that for channel 2 [96.2 vs. 121.3 kJ mol^-1 at the MP4SDQ/6-311++G(2d,p)//MP4SDQ/6-311G(d,p) level of theory]. Direct ab-initio dynamics calculations, carried out at the HF/6-311G(d,p) level, suggested that almost all the available energy is partitioned into the relative translational modes between fragments in channel 1, whereas 60% of the total available energy is partitioned into the internal and rotational modes of the HCO fragment in channel 2. In addition, rotational excitation of the a-axis of the FCO fragment is found in channel 1. The mechanisms of the dissociation reactions are discussed on the basis of the results.