Vibrational co-assignment of the calculated frequencies in the ground and two lowest excited electronic states

The feasibility of co-assignments of the vibrational frequencies in the ground and T1 and S1 excited electronic states has been demonstrated for trans-C2O2F2. Matrices analogous to the Duschinsky matrix were used to juxtapose the vibrational frequencies of this molecule calculated at the CASPT2/cc-pVTZ level in the ground S0 and excited triplet T1 and singlet S1 electronic states. The calculations suggest that the calculated CC and CF stretching frequencies of trans-C2O2F2 in these three electronic states should be mutually reassigned in comparison with the previous interpretation.