The ν2 bending vibrational structure of the $\tilde{X}$X̃ 2Σ+ state of MgNC
Authors: Fukushima Masaru , Ishiwata Takashi 
Published: October 2011

We have generated MgNC in supersonic free jet expansions and observed the laser induced fluorescence (LIF) of the \documentclass[12pt]{minimal}\begin{document}$\tilde{A}$\end{document}Ã 2Π–\documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ 2Σ+ transition. We measured the LIF dispersed spectra from the single vibronic levels of the \documentclass[12pt]{minimal}\begin{document}$\tilde{A}$\end{document}Ã 2Π electronic state of MgNC, following excitation of each ν2 bending vibronic band observed, i.e., the κ series of the (0,\documentclass[12pt]{minimal}\begin{document}$v_2^{\prime }$\end{document}v2′,0)–(0,0,0), \documentclass[12pt]{minimal}\begin{document}$v_2^{\prime }$\end{document}v2′ = 0, 1, 2, 4, and 6 vibronic bands. In the vibrational structure in the dispersed fluorescence spectra measured, the long progression of the ν2 bending mode in the \documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ 2Σ+ state is identified, e.g., up to \documentclass[12pt]{minimal}\begin{document}$v^{\prime \prime }_2 = 14$\end{document}v2′′=14 in the (0,6,0)–(0,\documentclass[12pt]{minimal}\begin{document}$v^{\prime \prime }_2$\end{document}v2′′,0) spectrum. This enables us to derive the potential curve of the ν2 bending mode in the \documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ 2Σ+ state. We used two kinds of models to obtain the potential curve; (I) the customary formula expressed in the polynomial series of the \documentclass[12pt]{minimal}\begin{document}$(v_2^{\prime \prime }+({d_2/}{2)})$\end{document}(v2′′+(d2/2)) term and (II) the internal rotation model. The potential curve derived from model (I) indicates the convergence of the bending vibrational levels at about 800 cm−1 from the vibrationless level of MgNC, which may correspond to the barrier height of the isomerization reaction, MgNC \documentclass[12pt]{minimal}\begin{document}$\rightleftharpoons$\end{document}⇌ MgCN, in the \documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ 2Σ+ state. Model (II) gives a simple picture for the isomerization reaction pathway with a barrier height of about 630 cm−1 from the vibrationless level of the more stable species, MgNC. This shows that the \documentclass[12pt]{minimal}\begin{document}$v^{\prime \prime }_2 = 8$\end{document}v2′′=8 bending vibrational level of MgNC is already contaminated by the \documentclass[12pt]{minimal}\begin{document}$v^{\prime \prime }_2 = 2$\end{document}v2′′=2 bending vibrational level of the isomer, MgCN, and implies that the isomerization reaction begins at the \documentclass[12pt]{minimal}\begin{document}$v^{\prime \prime }_2 = 8$\end{document}v2′′=8 level. The bending potential surface and the isomerization reaction pathway, MgNC \documentclass[12pt]{minimal}\begin{document}$\rightleftharpoons$\end{document}⇌ MgCN, in the \documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ 2Σ+ state are discussed by comparing the potential derived in this study with the surface obtained by quantum chemical calculation.