Multi-isotopologue analyses of new vibration-rotation and pure rotation spectra of ZnH and CdH

High resolution infrared emission spectra of ZnH, ZnD, CdH, and CdD have been recorded with a Fourier transform spectrometer. The v = 1 → 0 and v = 2 → 1 bands of ZnH, ZnD, CdH, and CdD, as well as the v = 3 → 2 band of ZnD were observed for the X²Σ⁺ ground electronic state. In addition, new rotational spectra have been recorded for CdH and CdD using a tunable far-infrared spectrometer, and pure rotational transitions in the v = 1 level of the ground state were measured. The new data were combined with the previous data from diode laser infrared spectra and pure rotation spectra of ZnH/ZnD and CdH/CdD available in the literature. The data from all isotopologues were fitted together using a Dunham-type energy level expression for ²Σ⁺ states, and Born-Oppenheimer breakdown correction parameters were obtained. The equilibrium rotational constants (B_e) of ⁶⁴ZnH, ⁶⁴ZnD, ¹¹⁴CdH, and ¹¹⁴CdD were determined to be 6.691332(17), 3.402156(7), 5.447074(18), and 2.750761(6) cm⁻¹, respectively, and the associated equilibrium internuclear distances (r_e) are 1.593478(2), 1.593001(2), 1.760098(3), and 1.759695(2) Å, respectively. Simple reduced mass scaling for the spin-rotation interaction constants of ZnH and CdH fully accounted for their isotopologue dependence, and no Born-Oppenheimer breakdown correction was required for these parameters.