Formation of XNCO species (X = F, Cl) through matrix-isolation photochemistry of XSO2NCO molecules

The photochemistries of the molecules ClSO2NCO and FSO2NCO isolated in solid argon matrices at ∼10 K have been investigated. After photolysis of the matrices with broad-band UV–visible radiation (200 ≤ λ ≤ 800 nm) the products were identified by their IR spectra. ClSO2NCO decomposes in two steps. In the first place, the photolysis gives a 1:1 molecular complex between SO2 and ClNCO. In the second step, ClNCO decomposes in different parallel photochemical channels to give ClNO, NO, CO and the ClCO· radical, while SO2, transformed from a complexed to an uncomplexed form, remains stable on photolysis. The SO2:ClNCO molecular complex was theoretically investigated by ab initio and DFT methods. Based on the comparison with the experimental findings, a structure in which the lone pair of one of the oxygen atoms of the SO2 unit interacts with the unoccupied σ*Cl–N orbital of ClNCO was proposed. On the other hand, FSO2NCO remains almost photostable when exposed to similar conditions, with the only formation of FNCO and CO in very small proportions.