A Theoretical Study of MgNC and MgCN in the X̃2Σ + Electronic State

Abstract

The MgNC radical was the first Mg-containing species to be observed in interstellar space. This fact has stimulated considerable spectroscopic interest in this molecule, and in its isomer MgCN, but nevertheless the only rotationally resolved spectroscopic data presently available for X̃ 2Σ + MgNC comprise the rotational spectrum (K. Kawaguchi et al., 1993, Astrophys. J. 406, L39–L42; K. Ishii et al., 1993, Astrophys. J. 410, L43–L44; M. A. Anderson and L. M. Ziurys, 1994, Chem. Phys. Lett. 231, 164–170; E. Kagi et al., 1996, J. Chem. Phys. 104, 1263–1267; E. Kagi and K. Kawaguchi, J. Mol. Spectrosc. 2000, 199, 309–310) together with a few vibronic bands, all originating in the vibronic ground state and belonging to the à 2Π← X̃ 2Σ + electronic transition (R. R. Wright and T. A. Miller, 1999, J. Mol. Spectrosc. 194, 219–228). For MgCN, only the rotational spectrum in the vibrational ground state is known (M. A. Anderson, T. C. Steimle, and L. M. Ziurys, 1994, Astrophys. J. 429, L41–L44). We report here potential energy surfaces calculated by the Averaged Coupled-Pair Functional (ACPF) method with TZ3P+f (Mg), TZ2P+f(N,C) basis sets including core-valence correlation due to the Mg 2s and 2p electrons. The ab initio results are used for determining the standard spectroscopic constants of X̃ 2Σ + MgNC and MgCN. Also, we report variational calculations of the rotation–vibration energies, and variational simulations of the lowest rotation–vibration bands, carried out with the MORBID program system (P. Jensen, 1988, J. Mol. Spectrosc. 128, 478–501). We hope that our theoretical results will encourage and facilitate further characterization of X̃ 2Σ + MgNC and MgCN by high-resolution spectroscopy.