The electronic spectra of CH2XOH (X = F, Cl, Br):: A comparative study

Excited states of the halogenated methanol derivatives CH2XOH (X = F, Cl, Br) relevant to atmospheric chemistry are investigated with use of ab initio multireference configuration interaction (MRD-CI) calculations. For CH2FOH three characteristic dipole allowed transitions were computed: 1(1)A"<--X(1)A' at 7.89 eV,2(1)A''<--X(1)A' at 9.03 eV, and 3(1)A" <-- X(1)A' at 10.21 eV. The first dipole allowed transitions in CH2ClOH are computed with 1.5 eV lower excitation energies (at 7.32 eV (1(1)A"<--X(1)A') and around 8 eV (2(1)A'<--X(1)A' and 2(1)A''<--X(1)A')). The first transitions in CH2BrOH are calculated with excitation energies of 6.29 (1(1)A"<--X(1)A'), 6.67 (2(1)A'<--X(1)A'), and 7.59 eV (2(1)A"<--X(1)A'). These differences can be understood due to the influence of the different charge distributions at the halogen atoms.