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 A˜2Π−X˜2Σ+ transition. In addition to the two vibronic bands, 210, κ2Σ(+)- and 220, κ2Π−2Σ+, reported previously, the 220, μ2Π1∕2−2Σ+ vibronic subband was found just above the 210 band. The most remarkable feature of this subband is unexpected rotational structure of the A˜ (020) μ2Π1∕2 level, showing the splitting of the e and f sublevels. On the basis of the fact that the A˜ (020) μ2Π1∕2 level lies very close to the A˜ (010) κ2Σ(+)2level, the e∕f splitting is ascribed to P-type doubling which is induced by Coriolisinteraction between these two bending vibronic levels. Introducing the Coriolis coupling terms arising from the G-uncoupling operator, −J±G∓22, and the spin-Coriolis interaction,S±G∓22, into the rotational Hamiltonian, this unexpected rotational structure has been analyzed. This P-type doubling would be one of the rare examples exhibiting the Coriolisinteraction between two bending vibronic levels with Δv2=±1 and Δl=∓1. Through the molecular constants of the A˜ (010) κ2Σ(+), (020) κ2Π, and μ2Π1∕2 levels, the Renner-Teller vibronic structure of the ν2 bending mode in the A˜2Π state has been characterized. The observed vibronic bands analyzed in this study show some anomalies in the band intensities. Based on the information of the ν2 bending vibronic structure derived from the present analyses, we discuss the intensity anomalies.

This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (C), 16510078, 2004.