Oxidation of methylene in low-temperature matrices

Abstract

The matrix photochemistry of CH₃l and its fully deuterated analogue at 4.2 K has been shown to proceed mainly through the intermediacy of methylene. The FTIR spectrum taken after photolysis of CH₃l in a nitrogen matrix shows that diazomethane is produced. Furthermore, the nature of the photooxidation products in ¹⁶O₂- or ¹⁸O₂-doped argon matrices support mechanisms in which methylene and molecular oxygen react. Weak IR bands which could not be attributed to known oxidation end products or intermediates could be tentatively assigned to dioxirane by comparison with previous ab initio calculations. If this is indeed the case then the appearance of CH₂O₂ in its cyclic form rather than its open-chain isomer indicates that either: (i) dioxirane is a primary product or (ii) the activation energy barrier between the forms is surmounted by photolysis as observed in other carbonyl oxide systems or (iii) the formaldehyde product is formed in a matrix by the efficient breakdown of peroxymethylene (by analogy with the gas-phase decomposition of CHCIOO, peroxychloromethylene).