The ν2 bending vibrational structure of the (X)over-tilde 2Σ+ state of MgNC

We have generated MgNC in supersonic free jet expansions and observed the laser induced fluorescence (LIF) of the (A) over tilde (2)Pi-(X) over tilde (2)Sigma(+) transition. We measured the LIF dispersed spectra from the single vibronic levels of the (A) over tilde (2)Pi electronic state of MgNC, following excitation of each nu(2) bending vibronic band observed, i.e., the kappa series of the (0,upsilon'(2),0)-(0,0,0), upsilon'(2) = 0, 1, 2, 4, and 6 vibronic bands. In the vibrational structure in the dispersed fluorescence spectra measured, the long progression of the nu(2) bending mode in the (X) over tilde (2)Sigma(+) state is identified, e. g., up to upsilon ''(2) = 14 in the (0,6,0)-(0,upsilon ''(2),0) spectrum. This enables us to derive the potential curve of the nu(2) bending mode in the (X) over tilde (2)Sigma(+) state. We used two kinds of models to obtain the potential curve; (I) the customary formula expressed in the polynomial series of the (upsilon ''(2) + (d(2)/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 reversible arrow MgCN, in the (X) over tilde (2)Sigma(+) 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 upsilon ''(2) = 8 bending vibrational level of MgNC is already contaminated by the upsilon ''(2) = 2 bending vibrational level of the isomer, MgCN, and implies that the isomerization reaction begins at the upsilon ''(2) = 8 level. The bending potential surface and the isomerization reaction pathway, MgNC reversible arrow MgCN, in the (X) over tilde (2)Sigma(+) state are discussed by comparing the potential derived in this study with the surface obtained by quantum chemical calculation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640024]