Calculations of magnetic hyperfine structure constants for the low-lying rovibrational levels of LiH, HF, CH+, and BH Original Research Article

Spin-rotation constants for the six lowest vibrational states and the first excited end-over-end rotational state were calculated for several isotopomers of the X 1Σ+ diatomic molecules: LiH, HF, CH+ and BH. For the ground vibrational state, the rotational dependence of the spin-rotation constant was also investigated and was found to be very weak. The electronic calculations were done at various levels of the polarization propagator approximation using atomic basis sets adapted for calculations of magnetic properties. The calculated spin-rotation constants for the isotopomers of LiH and HF, namely their rovibrational dependence, are in good agreement with the available experimental data. The extremely large values of the spin-rotation constants of C and B in CH+ and BH previously predicted by coupled perturbed Hartree-Fock calculations at the equilibrium internuclear distances were confirm by the present correlated and rovibrational averaged calculations. For the ground vibrational and first rotational state the spin-rotation constant of B in 11BH in 11CH+ are predicted to be −459.70 and −1186.15 kHz, respectively. The results are discussed in the light of recent calculations of the nuclear quadrupole coupling constants, since the relative strengths of both the magnetic and electric parameters determined the resulting pattern of the hyperfine structure of molecular rovibrational spectra. Improved experimental values for the nuclear magnetic shielding constants of HF (σF = 418.0 ± 2.0, σH = 28.6 ± 2.0) at the equilibrium geometry were derived from recent measurements and calculated diamagnetic contributions.