Electronic States of CH and NH

Ab initio calculations (LCAO–MO–SCF) are performed on a series of valence levels of the molecules CH and NH⁺. Correlation energies are estimated semiempirically from corresponding atomic data. Close agreement with experiment is found for known states for a series of molecular properties such as equilibrium internuclear distances, vibration frequencies, term values, and dissociation energies. A low‐lying ${}^4{\Sigma }^{-}$ state in CH is calculated to lie 7500 cm⁻¹ above the $X^2\Pi$ state. No observable quartet transition could be found for CH, while for NH⁺ a ${}^4{\mathrm{\Pi –}}^4{\Sigma }^{-}$ transition should occur in the region of 1000 Å. Other qualitative differences in the observed spectra of the two molecules are discussed. Finally a value of $D_0^0({\mathrm{NH}}^{+}\text{)\hspace{0.17em}=\hspace{0.17em}3.4}\mathrm{eV}$ is calculated.