THE LOW-LYING BENDING VIBRONIC BANDS OF THE MgNC $\tilde{A}$ $^2\Pi$ -- $\tilde{X}$ $^2\Sigma^+$ TRANSITION: ANALYSIS OF THE P-TYPE DOUBLING

Abstract

We have generated MgNC in supersonic free jet expansions, and measured the laser induced fluorescence excitation spectra of the Mg-N-C bending vibronic bands of the $\tilde{A}$ $^2\Pi$ -- $\tilde{X}$ $^2\Sigma^+$ transition. In addition to the two vibronic bands, $2_0^1$, $\kappa$ $^2\Sigma^{(+)}$ -- and $2_0^2$, $\kappa$ $^2\Pi$ -- $^2\Sigma^+$, reported by Wright and Miller} \underline{\textbf{194}}, 219 (1999).}, the $2_0^2$, $\mu$ $^2\Pi_{\frac{1}{2}}$ -- $^2\Sigma^+$ sub-band were found just above the $2_0^1$ vibronic band. The most remarkable feature of this newly observed sub-band is unexpected rotational structure on the upper vibronic level, $\tilde{A}$ (020) $\mu$ $^2\Pi_{\frac{1}{2}}$; i.e. the rotational levels show splitting into the $e$ and $f$ sub-levels and have different rotational constants on the each rotational sub-level. Introducing the Coriolis coupling terms of $-J^{\pm}G^{\mp}$ and $S^{\pm}G^{\mp}$, which could be called the {\bf G}-uncoupling operator and the spin-Coriolis interaction, respectively, into the rotational Hamiltonian, this unexpected rotational structure has been analyzed quite reasonably.