Many-body calculations of hyperfine constants in diatomic molecules. I. The ground state of 16OH

Magnetic hyperfine parameters (Frosch and Foley parameters) have been computed for the 2Π ground state of 16OH by use of many-body perturbation theory. The computations are complete to third order in the many-body expansion, and they were repeated for a series of internuclear distances around re to reproduce the vibrational dependencies of the parameters. Parameters were computed for the three lowest vibrational levels, and were found to be within 1%–2% of the very accurate experimental values. The rather strong vibrational dependencies of the parameters were reproduced with accuracies of 80%–90%. Finally, centrifugal distortion corrections to the magnetic hyperfine parameters were also computed, and for the one parameter (dD) observed, the error was about 5%. The vibrational wave functions needed were obtained from a published accurate CI potential curve. Thus, no empirical results are incorporated in the present ab initio calculations.