Valence excited states of CH. I. Potential curves

Ab initio CI calculations have been performed over a wide range of internuclear distances (1.00-20.00 bohr) to obtain the potential curves for the first five valence excited states of CH; X2II, a4Σ -, A 2Δ, B2Σ-, and C2Σ+. Results, with known experimental values in parentheses, are Re(X2II) = 2.113 (2.116) bohr, R e(a4Σ-) = 2.053 bohr; R e(A2Δ) = 2.083(2.083) bohr, Re(B 2Σ) = 2.216(2.20) bohr, Re(C2Σ +) = 2.100(2.105) bohr; De(X2II) = 3.51(3.63) eV, De(a4Σ-) = 2.84 eV, D e(A2Δ) = 1.90(2.01) eV, De(B 2Σ-) = 0.23(0.40) eV, and De),(C 2Σ+) = 0.78(0.94) eV. Potential maxima of heights 1284 and 3228 cm-1 are calculated for the B2Σ - and C2Σ+ states, respectively. These maxima are attributed to avoided curve crossings. The a4Σ state, not observed experimentally, is estimated to lie between 0.62 and 0.76 eV above the X2II state.