Quantum chemical computation of the spectroscopic constants of the states of CBrCl and its heat of formation

The relative energies of the X ˜ , a ˜ and A ˜ 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.