Ultraviolet Spectrum and Reaction Kinetics of the Formyl Radical

Article abstract of DOI:10.1021/j100440a001

A transient ultraviolet adsorption attributed to the formyl radical, HCO, was produced by flash photolysis of water vapor in the presence of CO.For CO saturated with H2O at a total pressure of 1 atm, the formation of HCO is complete within c.a. 60 μs, after which it undergoes second-order decay, with k/ε(230 nm) = (1.5 +/- 0.2)e7 cm s^-1.During the relatively slow formation reaction (H + CO (+M) -> HCO), the competing reaction H + HCO -> H2 + CO is significant.By employing the H2O + CH4 system as an actinometer to determine the amount of H2O dissociated by the flash (discussed elsewhere) and by computer modeling the observed formation and decay of HCO as a function of CO pressure, the following absolute rate constants were obtained: k₃(H+CO(+M)->HCO) + (3.6 +/- 0.9)e7 M^-2 s^-1 for M = CO, (5.8 +/- 0.6)e7 M^-2 s^-1 for M = CH4, and (3.8 +/- 0.4)e7 M^-2 s^-1 for M = H2, k₄(HCO+HCO->products) = (1.4 +/- 0.3)e10 M^-2 s^-1, and k₅(H+HCO->products) = (6.9 +/- 1.7)e10 M^-2 s^-1.The molar extinction coefficient ε(HCO,230 nm) = 941 +/- 171 M^-1 cm^-1.