Calculation of potential energy curves for the process ${\mathrm{C}}^{3+}$(2l)+H(1s) →${\mathrm{C}}^{2+}$(nln’l’${;}^1$L)+${\mathrm{H}}^{+}$ using spin-coupled valence-bond theory theory

Potential energy curves of ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ symmetry have been calculated for the process ${\mathrm{C}}^{3+}$(2l)+H(1s) →${\mathrm{C}}^{2+}$(nln’l’ ${;\mathrm{}}^1$L)+${\mathrm{H}}^{+}$ by means of the spin-coupled valence-bond theory. Very large basis sets of Slater functions have been used in order to describe reasonably well a large number of states. A total of eleven states has been examined, the asymptotic energies of which match the experimental values closely: errors are 0.02–0.9 eV over a range of 45 eV. The only exception is the ${\mathrm{C}}^{2+}$(2s3d${;\mathrm{}}^1$D)+${\mathrm{H}}^{+}$ state where there is a discrepancy of 2 eV which we attribute to remaining deficiencies in the 3d basis set. The charge-transfer states ${\mathrm{C}}^{3+}$(2s${;\mathrm{}}^2$S)+H(1s)(state 7) and ${\mathrm{C}}^{3+}$(2p${;\mathrm{}}^2$P)+H(1s) (state 11) show very strongly avoided intersections with at least four other states. We conclude that charge-transfer studies of this system must take into account a minimum of five strongly coupled states. Later studies will concentrate on the ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ states and on the radial couplings.