Ab initio MRD-CI study of excited states of chloromethanol ClCH 2OH and photofragmentation along C–O and C–Cl cleavage

Abstract

Large-scale ab initio multi-reference configuration interaction calculations are carried out for ground and excited states of chloromethanol ClCH 2OH to investigate photofragmentation processes relevant to atmospheric chemistry. Five low-lying excited states ( 1 3 A″ , 1 3 A ′ , 1 1 A″ , 2 1 A ′ and 2 3 A ′ ) in the energy range between 6.8 and 8.5 eV are found to be highly repulsive for C–Cl elongation leading to CH 2 OH( X 2 A ′) and Cl( 2 P) . Photodissociation along the C–O bond leading to CH 2 Cl( X 2 B 2) and OH( X 2Π) has to overcome a small barrier of about 0.3 eV because the low-lying excited states 1 1 A″ , 1 3 A ′ and 1 3 A″ become repulsive only after the C–O bond is elongated by about 0.2 Å.