Photolysis of Ketene at 193 nm and the Rate Constant for H + HCCO at 297 K

Abstract

The 193 nm photolysis of ketene was studied by measuring the amount of atomic hydrogen produced when very dilute ketene/Ar and ketene/H2 mixtures were irradiated by a single pulse from an ArF excimer laser. Absolute concentrations of atomic hydrogen were monitored over a time interval of 0−2.5 ms by using Lyman-α atomic resonance absorption spectroscopy (ARAS). Four different photodissociation channels of ketene were identified: H2CCO + hν gives (a) CH2(3B1) + CO; (b) CH2(1A1) + CO; (c) HCCO + H; and (d) C2O(b1Σ+) + H2. The quantum yields for each channel were measured as φa = 0.628, φb = 0.193, φc= 0.107, and φd = 0.072, respectively. To explore the secondary chemistry that occurred when using higher pressure H2CCO/Ar mixtures, a mechanism was constructed that used well-documented reactions and, for most processes, rate constants that had already been accurately determined. Modeling studies using this mechanism showed the [H] profile to be determined largely by the rate of the reaction H + HCCO → CH2 + ...