Electronic transition moment for the B 2Σ+–X 2Σ+ emission of CN. Analysis of dependence on the internuclear distance

Abstract

The dependence of the electronic transition moment Re(R) for the B 2Σ+–X 2Σ+ transition of CN on the internuclear distance R is determined by an analysis of the relative intensity of its emission spectrum. In the present analysis of the spectrum, the relative values of Re(R) are directly evaluated by use of the vibrational integrals, 〈v′‖Rn‖v″〉 (n=1,2,...), instead of the r-centroid approximation, which is found to be inadequate particularly in the tail bands (v′≥10). The validity of the r-centroid approximation is discussed on the basis of the Rydberg–Klein–Rees (RKR) potentials of the B 2Σ+ and X 2Σ+ states. The R dependence of the Re(R) value is interpreted in terms of the electronic wave function of B 2Σ+; the configuration-interaction (CI) coefficients for the electronic configurations of the B 2Σ+ state are estimated. The CI coefficients obtained in the present study, as well as those for the A 2Πi state derived previously from a similar analysis of the electronic part of the spin–orbit constant A(R) for A 2Πi, are used to evaluate the electronic part of the spin–orbit matrix element between the B 2Σ+ and A 2Πi states HSOel. The HSOel values are predicted to be −25 and −21 cm−1 at R=0.97 and 1.3 Å, respectively, being consistent with those determined experimentally in our previous study, −31 and −21 cm−1, respectively.