Rotationally Resolved (1 + 1‘) Resonance-Enhanced Multiphoton Ionization (REMPI) of CaR (R = H, D) in Supersonic Beams:  CaR X 2Σ+ (υ‘ ‘ = 0) → CaR* B 2Σ+ (υ = 0, 1) → CaR+ X Σ+

We report on a laser-spectroscopic study of the CaH and CaD radicals in a supersonic beam, generated in a reaction of laser-sputtered Ca atoms and a pulsed beam of H2 or D2, seeded in helium. The rotational levels of the electronic ground-state X 2Σ+ (υ‘ ‘ = 0, N‘ ‘ ≤ 10) were probed by two-color resonance ionization mass spectrometry(1 + 1‘) resonance-enhanced multiphonon ionization (REMPI)via the intermediate B 2Σ+ (υ = 0, 1) rovibronic levels. Rotational constants for the B-state were derived, including the spin splitting parameters γυ‘, which have been determined in the case of CaD for the first time:  γ0 = −0.409(7) cm-1 and γ1 = −0.398(8) cm-1 for CaD (B Σ+), and γ0 = −0.792(15) cm-1 and γ1 = −0.765(16) cm-1 for CaH (B 2Σ+). The comparison between the rotational level energies of the F1 and F2 spin substates of the two isotopomers revealed the onset of perturbation in CaH B 2Σ+ (υ = 0), at N‘ ≅ 0, by the presence of the vibronic state A 2Π (υ = 1). Although this perturbation is documented for υ‘ ≥ 1, it had not been previously recognized for υ‘ = 0. The rotational populations observed in X 2Σ+ (υ‘ ‘ = 0) for the two isotopomers could be associated with different average rotational temperature values for CaD and CaH:  Trot = 52 (± 7) and Trot = 85 (± 11) K, respectively.