Flash photolysis of ketene. Photolysis mechanism and rate constants for singlet and triplet methylene

Abstract

The photochemistry of ketene has been studied, using flash photolysis coupled with end product analysis, for wavelengths above 160 nm. The data were analysed numerically, enabling the proposed reaction mechanisms to be assessed quantitatively. The major novel feature is the observation of products normally derived from CH₂¹A₁ at high pressures where deactivation to CH₂³B₁ is expected to be complete. It is suggested that these products derive from CH₂¹B₁ is expected to be complete. It is suggested that these products derive from CH₂¹B₁. The data require that this state is comparatively stable with respect to collisional deactivation, but reacts with H₂(k= 2 × 10^–11 cm³ molecule^–1 s^–1) and CH₂CO (k= 3 × 10^–11 cm³ molecule^–1 s^–1). These rate constants depend on an assumed radiative lifetime (1/e) for CH₂¹B₁ of 10^–6 s. An anomalously high yield of acetylene is found at low pressures in the presence of hydrogen. Rate constants for CH₂¹A₁ with CH₂CO and CH₂³B₁ with C₂H₂, NO, O₂ and CO are reported.