Photochemistry of matrix-isolated and thin film acid chlorides: Quantum yields and product structures

Ultraviolet photoexcitation of matrix-isolated CH3COCl, CH3CH2COCl, and CH3 CH2CH2CH2COCl produces HCl . CH2=C=O, HCl . CH3CHC=C=O, and HCl . CH3CH2CH2 CHC=C=O complexes. We report precursor and matrix dependent reaction quantu m yields. Quantum yield values decrease with increasing alkyl chain length due to a reduced number of alpha H-atoms available for the elimination reac tion and steric considerations. We found quantum yields in neat matrixes to be roughly half that in argon or xenon matrixes and assign structures for HCl and ketene complexes in argon and xenon matrixes by comparing IR spectr a to ab initio electronic structure calculations. In argon matrixes, the pr oduct complex HCl frequency is strongly shifted whereas the ketene remains unshifted with respect to matrix-isolated ketene. In xenon matrixes, HCl . ketene complexes display absorption bands indicative of two distinct struct ures. Differences between HCl . ketene structures in argon and xenon matrix es are attributed to size differences of the matrix lattice.