The laser magnetic resonance spectra of imine (NH) and its isotopes

Laser magnetic resonance spectra at submillimetre wavelengths of 14 NH (v = 0 and v = 1), 15 NH (v = 0) and 14 ND (v = 0 and v = 1) have been measured and analysed. Values of the hyperfine parameters for the different isotopic species are derived which are consistent with each other but are not sufficiently precise to show a dependence upon internuclear distance. Ab initio calculations of the dipole-dipole hyperfine parameters agree with experiment but calculations by others of the Fermi contact parameters are not supported by these experiments. More precise values for the rotational constants and the equilibrium internuclear distance than have been obtained from optical spectroscopy are derived. The effective spin-spin parameter λ is found to vary little with vibrational state near the bottom of the potential well. Ab initio calculations reproduce the magnitude of λ but overestimate its dependence upon internuclear distance. No precise values for the g-factors could be obtained. Somewhat larger populations of vibrationally excited NH radicals were found than might be expected from a reaction between F atoms and NH 2 radicals.