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

Direct ab-initio dynamics calculations have been applied to the photodissoc iation of the HFCO molecule on the potential energy surface at the triplet state in order to elucidate its reaction mechanism and to determine the ene rgy partitioning in the products. Two reaction channels, HFCO(T-1) --> H(S- 2) + FCO(X(2)A') and HFCO(T-1) --> F(P-2) + HCO(X(2)A') (denoted as channel s 1 and 2, respectively) were considered as decay processes of HFCO(T-1). A b-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 t heory]. Direct ab-initio dynamics calculations, carried out at the HF/6-311 G(d,p) level, suggested that almost all the available energy is partitioned into the relative translational modes between fragments in channel 1, wher eas 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 mec hanisms of the dissociation reactions are discussed on the basis of the res ults.