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

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<sub>2</sub> or D<sub>2</sub>, seeded in helium. The rotational levels of the electronic ground-state <i>X</i> <sup>2</sup>Σ<sup>+</sup> (<i>υ</i>‘ ‘<i><sup> </sup></i><sup></sup>= 0, <i>N</i>‘ ‘ ≤ 10) were probed by two-color resonance ionization mass spectrometry(1 + 1‘) resonance-enhanced multiphonon ionization (REMPI)via the intermediate <i>B</i> <sup>2</sup>Σ<sup>+</sup> (<i>υ</i><i>‘</i> = 0, 1) rovibronic levels. Rotational constants for the <i>B</i>-state were derived, including the spin splitting parameters <i>γ</i><i><sub>υ</sub></i>‘, which have been determined in the case of CaD for the first time:  γ<sub>0</sub> = −0.409(7) cm<sup>-1</sup> and γ<sub>1</sub> = −0.398(8) cm<sup>-1</sup> for CaD (<i>B </i>Σ<sup>+</sup>), and γ<sub>0</sub> = −0.792(15) cm<sup>-1</sup> and γ<sub>1</sub> = −0.765(16) cm<sup>-1</sup> for CaH (<i>B</i> <sup>2</sup>Σ<sup>+</sup>). The comparison between the rotational level energies of the F<sub>1</sub> and F<sub>2</sub> spin substates of the two isotopomers revealed the onset of perturbation in CaH <i>B</i> <sup>2</sup>Σ<sup>+</sup> (<i>υ</i><i>‘</i> = 0), at <i>N</i>‘ ≅ 0, by the presence of the vibronic state <i>A</i> <sup>2</sup>Π (<i>υ</i><i>‘</i> = 1). Although this perturbation is documented for <i>υ</i>‘ ≥ 1, it had not been previously recognized for <i>υ</i>‘ = 0. The rotational populations observed in <i>X</i> <sup>2</sup>Σ<sup>+</sup> (<i>υ</i>‘ ‘ = 0) for the two isotopomers could be associated with different average rotational temperature values for CaD and CaH:  <i>T</i><sub>rot</sub> = 52 (± 7) and <i>T</i><sub>rot</sub> = 85 (± 11) K, respectively.