The isotopic dependence of the spin–rotation interaction: the rotational spectrum of cadmium hydride in its X2Σ+ state

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

“…The isotopic dependence of the spin-rotation interaction constant (c), derived by Brown and Watson [50], was implemented in our fitting program, and we also included a simple vibrational dependence for this constant. We show that many of the Born-Oppenheimer breakdown correction parameters reported by Varberg and Roberts [48] vanish if the vibrational dependences of rotational and spin-rotation interaction constants are taken into account properly.…”

“…The far-infrared absorption spectra of CdH and CdD were recorded using the NIST TuFIR spectrometer in Boulder, Colorado, and the experimental conditions were exactly the same as those described in the recent paper of Varberg and Roberts on these molecules [48]. The CdH and CdD molecules were generated in a quartz discharge tube that had seven equally spaced 1-cm-deep depressions in it, into which cadmium metal was placed.…”

“…Magnetic hyperfine structure arising from the 1 H or 2 D nucleus was present in all these spectra, but was fully resolved only for the lowest-N transitions of CdH. We fitted the hyperfine structure of these low-N rotational lines of CdH in the v = 1 level, and found it to be 10% larger than that in the corresponding rotational lines within the v = 0 level [48]. This determination allowed us to predict hyperfine splittings over the full range of v = 1 rotational levels studied, which is required for an accurate analysis of the observed line shapes, as described in [48].…”

“…Millimeter-wave and far-infrared spectra of ZnH and ZnD were obtained by Goto et al [46] and Tezcan et al [47], respectively, and several rotational lines in the v = 0 level of the X 2 R + ground state were measured. Recently, Varberg and Roberts [48] recorded the far-infrared spectra of CdH and CdD, and observed rotational transitions in the v = 0 level of the X 2 R + ground state. They performed a multi-isotopologue fit to their data, but overlooked the vibrational dependence of the rotational and spin-rotation interaction constants.…”

“…In addition, we have recorded new far-infrared spectra of CdH and CdD, and observed several rotational transitions in the v = 1 level of the X 2 R + state. We have combined our new data with those obtained from the previous vibration-rotation and pure rotation spectra [44][45][46][47][48], and performed multi-isotopologue fits for ZnH and CdH using a Dunham-type energy level expression [49] that was modified for 2 R + states. The isotopic dependence of the spin-rotation interaction constant (c), derived by Brown and Watson [50], was implemented in our fitting program, and we also included a simple vibrational dependence for this constant.…”