Laser spectroscopic study of the B/B″²Σ⁺–X²Σ⁺ (9-0), (10-0), (11-0) and (18-0) bands of CaH

Calcium monohydride is an astronomically important molecule. Despite the long history of work on this molecule, discrepancies still exist between experiment and theory for the higher vibrational levels of the B/B′²Σ⁺ state. We report on rotational-vibrational-electronic transitions to the B/B′²Σ⁺ state which we have assigned to the B/B′²Σ⁺ (v = 9, 10, 11 and 18) – X²Σ⁺ (v = 0) transitions. The energy spacing of the higher lying vibrational levels of the B/B′²Σ⁺ state alternates strongly with vibrational quantum number as predicted by the coupled-channel calculations of Carlsund-Levin et al. (2002). We confirm that this alternation extends all the way from v = 9 to v = 20.