Interpretation of Photoelectron Spectra of Halomethanes

Theoretical studies of the electronic structure of chloromethanes (CH4−nCln, where n=1∼4) were carried out by the CNDO/2 method. The resulting Koopmans’ theorem ionization energies were generally in good agreement with the experimental data available, and somewhat different assignments from those previously reported were obtained for the nonbonding orbitals. A “sum rule” was employed for interpreting the photoelectron bands of three series of di- and poly-halomethanes (chloro-, bromo-, and iodo-methanes) in terms of some localized molecular orbitals. Reasonable assignments were derived for the photoelectron spectra of all these halomethanes and the resulting assignments for the chloromethanes were in good accord with those obtained from the CNDO/2 calculation.