Rotationally resolved (1+1′) resonance-enhanced multiphoton ionization (REMPI) of CaR (R = H, D) in supersonic beams:: CaR X 2Σ+ (v′′=0) → CaR* B 2Σ+ (v′=0, 1) → CaR+ X 1Σ+

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 H-2 or D-2, seeded in helium. The rotational levels of the electronic ground-state X (2)Sigma(+) (nu" = 0, N" less than or equal to 10) were probed by two-color resonance ionization mass spectrometry-(1 + 1') resonance-enhanced multiphonon ionization (REMPI)-via the intermediate B (2)Sigma(+) (nu' = 0, 1) rovibronic levels. Rotational constants for the B-state were derived, including the spin splitting parameters gamma(nu)', which have been determined in the case of CaD for the first time: gamma(0) = -0.409(7) cm(-1) and gamma(1) = -0.398(8) cm(-1) for CaD (B (2)Sigma(+)), and gamma(0) = -0.792(15) cm(-1) and gamma(1) = -0.765(16) cm(-1) for CaH (B (2)Sigma(+)). The comparison between the rotational level energies of the F-1 and F-2 spin substates of the two isotopomers revealed the onset of perturbation in CaH B (2)Sigma(+) (nu' = 0), at N' congruent to 0, by the presence of the vibronic state A (2)Pi (nu' = 1). Although this perturbation is documented for nu' greater than or equal to 1, it had not been previously recognized for nu' = 0. The rotational populations observed in X (2)Sigma(+) (nu" = 0) for the two isotopomers could be associated with different average rotational temperature values for CaD and CaH: T-rot = 52 (+/- 7) and T-rot = 85 (+/- 11) K, respectively.