Spectroscopy of the X1Σ+, a1π and B1Σ+ electronic states of mgs

Abstract

The spectra of some astrophysical sources contain signatures from molecules containing magnesium or sulphur atoms. Therefore, we have extended previous studies of the diatomic molecule \chem{MgS}, which is a possible candidate for astrophysical detection. Microwave spectra of X$^1\Sigma^+$ , the ground electronic state, were reported in 1989\footnote{S. Takano, S. Yamamoto and S. Saito, Chem. Phys. Lett. \textbf{159}, 563-566 (1989).} and 1997\footnote{K. A. Walker and M. C. L. Gerry, J. Mol. Spectrosc \textbf{182}, 178-183 (1997).}, and the B$^1\Sigma^+$--X$^1\Sigma^+$ electronic absorption spectrum in the blue was last studied in 1970\footnote{M. Marcano and R. F. Barrow, Trans. Faraday Soc. \textbf{66}, 2936-2938 (1970).}. We have investigated the B$^1\Sigma^+$--X$^1\Sigma^+$ 0-0 spectrum of \chem{MgS} at high resolution under jet-cooled conditions in a laser-ablation molecular source, and have obtained laser-induced fluorescence spectra from four isotopologues. Dispersed fluorescence from this source identified the low-lying A$^1\Pi$ state near 4520 \wn. We also created \chem{MgS} in a Broida oven, with the help of a stream of activated nitrogen, and took rotationally resolved dispersed fluorescence spectra of the B$^1\Sigma^+$--A$^1\Pi$ transition with a grating spectrometer by laser excitation of individual rotational levels of the B$^1\Sigma^+$ state via the B$^1\Sigma^+$--X$^1\Sigma^+$ transition. These spectra provide a first observation and analysis of the A$^1\Pi$ state.