Quantum chemical computation of the spectroscopic constants of the X˜(1A′),a˜(3A″)andA˜(1A″) states of CBrCl and its heat of formation

The relative energies of the X˜,a˜andA˜ states of CBrCl and its atomization energy in the complete basis limit were determined by extrapolating (spin restricted) CCSD(T), MRCI and EOM-CCSD energies calculated with the aug-cc-pVxZ (x = T, Q, 5) basis sets which were corrected for core-valence correlation, scalar relativistic and spin-orbit coupling effects. The geometries and vibrational frequencies were calculated at the B3LYP/cc-pVTZ density functional and CASPT2/cc-pVTZ levels of theory. The predicted heat of formation at 298 K is 68.0 ± 1.0 kcal mol−1. The calculated singlet excited state vibrational frequencies and A˜←X˜ excitation energy are in close agreement with experiment.