15min:

MASARU FUKUSHIMA AND TAKASHI ISHIWATA, Faculty of Information Sciences, Hiroshima City University, Asa-Minami, Hiroshima 731-3194, Japan.

We have generated MgNC in supersonic free jet expansions, and measured the laser induced fluorescence excitation spectra of the Mg-NC stretching vibronic bands of the A ² -- X ^{2 +} transition. In addition to the bands already reported by Wright and Miller, the 3₀² and 3₀³ bands have been observed for the first time, and the molecular constants of the vibronic levels, (0,0,2) and (0,0,3), in the A ² state have been newly determined through rotational analysis of the observed bands. Comparing all of the spin-orbit constants, A_SO, on the vibrational levels for the two stretching modes, Mg-NC and C-N, obtained in this work and reported previously, we find opposite dependence of A_SO upon the two stretching vibrational modes, i.e.~A_SO increases with the excitation of the Mg-NC stretching vibrational mode, while it decreases with the excitation of the C-N mode. The experimental finding is supported by an attempt to calculate the dependence of A_SO upon the distance along the vibrational modes.