Ab initio MRD-CI study of excited states of chloromethanol ClCH2OH and photofragmentation along C–O and C–Cl cleavage

Large-scale ab initio multi-reference configuration interaction calculations are carried out for ground and excited states of chloromethanol ClCH2OH to investigate photofragmentation processes relevant to atmospheric chemistry. Five low-lying excited states (13A″, 13A′, 11A″, 21A′ and 23A′) in the energy range between 6.8 and 8.5 eV are found to be highly repulsive for C–Cl elongation leading to CH2OH(X2A′) and Cl(2P). Photodissociation along the C–O bond leading to CH2Cl(X2B2) and OH(X2Π) has to overcome a small barrier of about 0.3 eV because the low-lying excited states 11A″, 13A′ and 13A″ become repulsive only after the C–O bond is elongated by about 0.2 Å.