Enhancement of Parity-Violating Energy Difference of CHFClBr, CHFClI, and CHFBrI by Breaking the Cancellation among Valence Orbital Contributions

The enhancement of the parity-violating energy difference (PVED) by electronic excitation is studied for H2X2 (X = O, S, Se, Te), CHFClBr, CHFClI, and CHFBrI. To clarify the enhancement mechanism, the dihedral angle dependence of the PVED of H2X2 in excited states is studied. If the contribution from the highest occupied molecular orbital (HOMO) to the PVED in the ground state is larger than the sum of those from all occupied orbitals, the magnitude of the PVED in the first excited state may be much larger than that of the ground state due to cancellation breaking among valence orbital contributions. This enhancement is named cancellation breaking enhancement. The PVED enhancement is also studied for CHFClBr, CHFClI, and CHFBrI in excited states, and results are consistent with the cancellation breaking enhancement. When the PVED contribution from the HOMO is larger than any other contribution, the cancellation breaking enhancement hypothesis may provide the estimate of PVED in the first excited state from the HOMO contribution.