Should bromoform absorb at wavelengths longer than 300 nm?

摘要

A theoretical study of the low-lying singlet and triplet electronic states of CHBr_3 is presented. Calculations of excitation energies and oscillator strengths are presented using excited state coupled cluster response methods, as well as the complee active space self-consistent field method with the full Breit-Pauli Spin-orbit operator. These calculations predict that for CHBr_3 there is only one singlet state, the A~1A_2, that is accessible by wavelengths longer than 234 nm. It is, however, predicted to be very weakly abosrbing, but may strongly overlap at shorter wavelengths with a higher B~1E state, which itself is predicted to be strongly absorbing. There is one trplet state the a~3A_2, that lies well below the A~1A_2 state and has a predicted absorption maximum at about 720 nm. The band origin of the a~3A_2 is predicted to lie around 297 nm, but this C_3v symmetry minimum is calculated to be a second-order transition state, ultimately leading to dissociation to HCBr_2 + Br.