The ν_2 bending vibrational structure of the X?~2Σ~+ state of MgNC

摘要

We have generated MgNC in supersonic free jet expansions and observed the laser induced fluorescence (LIF) of the ?~2Π- X?~2Σ~+ transition. We measured the LIF dispersed spectra from the single vibronic levels of the A ~2 electronic state of MgNC, following excitation of each _2 bending vibronic band observed, i.e., the κ series of the (0,v2′,0)-(0,0,0), v2′ = 0, 1, 2, 4, and 6 vibronic bands. In the vibrational structure in the dispersed fluorescence spectra measured, the long progression of the 2 bending mode in the X?~2Σ~+ state is identified, e.g., up to v2″=14 in the (0,6,0)-(0,v2″,0) spectrum. This enables us to derive the potential curve of the 2 bending mode in the X 2Σ+ state. We used two kinds of models to obtain the potential curve; (I) the customary formula expressed in the polynomial series of the (v2″+(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 ? MgCN, in the X ~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 v2″=8 bending vibrational level of MgNC is already contaminated by the v2″=2 bending vibrational level of the isomer, MgCN, and implies that the isomerization reaction begins at the v2″=8 level. The bending potential surface and the isomerization reaction pathway, MgNC ? MgCN, in the X ~(2+) state are discussed by comparing the potential derived in this study with the surface obtained by quantum chemical calculation.