Knowledge Bank

We have used the RENNER program $systemb$ to make a detailed calculation of the rovibronic energies in the first excited electronic state, $A~2\Pi$, of the MgNC radical. This calculation was based on recent ab initio surfaces $(MRSDCI(+Q)/[TZ3P+f(Mg)$, aug-cc-$pVQZ(NandC)])c$ for the Renner-degenerate electronic states. Previous calculations of vibronic $energiesc$ employing the same ab initio data in conjunction with perturbation $expressionsd$ suggested that an observed band belonging to the $A~2\Pi \leftarrow X~2\Sigma +$ electronic $transitione$ should be reassigned. The present work confirms this conclusion which is further substantiated by the rotational structures calculated in the vibronic states, and by Franck-Condon theory predicting relative intensities. $A~2\Pi$ MgNC affords an example of the ``classic'' Renner $effectf$ involving component electronic states with linear equilibrium geometries. We present detailed analyses of rovibronic wavefunctions aimed at providing further insight into the nature of the Renner interaction.