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 (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 CH2OH(X(2)A ') and Cl(P-2). Photodissociation along the C-O bond leading to CH2Cl((XB2)-B-2) and OH((XII)-I-2) 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 A.