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.