Calculated a4Σ−, A2Δ, B2Σ− States of CH

Abstract

Ab initio CI calculations have been performed over a wide range of internuclear distances to obtain the potential curves for three low‐lying excited electronic states, a⁴Σ⁻, A²Δ, B²Σ⁻, of CH. With the computed potential curves, vibration‐rotational levels are obtained by numerical integration of the radial Schrödinger equations for the motion of the nuclei. The term values are analyzed to yield the conventional spectroscopic constants. Results, with known experimental values in parentheses, are $R_e{\mathrm{(A\hspace{0.17em}}}^2\text{Δ)=2.074(2.082)\hspace{0.17em}}\mathrm{a.u.}$ , $R_e{\mathrm{(B\hspace{0.17em}}}^2{\Sigma }^{-}\text{)=2.208(2.200)\hspace{0.17em}}\mathrm{a.u.}$ , $R_e{\mathrm{(a\hspace{0.17em}}}^4{\Sigma }^{-}\text{)=2.047\hspace{0.17em}}\mathrm{a.u.}$ ; $D_e^0{\mathrm{(A\hspace{0.17em}}}^2\text{Δ)=1.89(2.01)\hspace{0.17em}}\mathrm{eV}$ , $D_e^0{\mathrm{(B\hspace{0.17em}}}^2{\Sigma }^{-}\text{)=0.17(∼ 0.40)\hspace{0.17em}}\mathrm{eV}$ , and $D_e^0{\mathrm{(a\hspace{0.17em}}}^4{\Sigma }^{-}\text{)=2.88\hspace{0.17em}}\mathrm{eV}$ . The computed spectroscopic constants are found to be within 4% of known experimental values. A potential maximum of height 1600 cm⁻¹ occurs in the computed potential curve of the B²Σ⁻ state. The a⁴Σ⁻ state, not known experimentally, is estimated to lie between 0.52 eV and 0.75 eV above the X²II ground state.