Theoretical study of the A 1Π–X 1Σ+ transition in C2B− Original Research Article

Three-dimensional potential energy functions have been generated for the A 1Π electronic state of C2B− using highly correlated electronic multireference configuration interaction wave functions. These were then employed in variational Renner–Teller calculations. The rotational constant B0 has been calculated to be 0.3971 cm−1, with ReCC=1.326 Å and ReCB=1.387 Å. Rovibronic levels for J=0, 1 and 2 are given for energies up to 3000 cm−1. Due to a large Renner–Teller parameter ϵ=0.4244 the bending states strongly interact. Based on the theoretical results the vibronic progression observed in the absorption spectrum of the A 1Π–X 1Σ+ transition of C2B− has been reassigned. The MRCI A 1Π–X 1Σ+ transition moment has been calculated to be 1.816 Debye for the equilibrium geometry of the A 1Π state, yielding a radiative lifetime of 91 ns.