Near threshold dynamics and dissociation energy of the reaction H2CO → HCO + H

The state-to-state dynamics of the gas phase reaction H2CO (v, J, Ka, Kc) + hv → H + HCO(v, N, S, Ka, Kc) have been explored in a supersonic free jet. Seven rotational states within the 2143 vibrational level of H2CO were excited and the population distribution of the HCO (v = 0, N, S, Ka, Kc) product states measured. The distributions are constrained severely by the available energy in the reaction with the lowest H2CO state producing HCO in only three rotational states. Careful matching of the H2CO and HCO energy levels leads to an estimate of the dissociation energy of the above reaction of 30328.5 ± 0.5 cm−, which lead us to an estimate of the standard heat of formation of the formyl radical of ΔHf0 = 42.5 ± 0.5 kJ mol−1.