Infrared diode laser spectra of MgH and MgD (X 2Σ+)

Abstract

Infrared absorption spectra of magnesium hydride in its 2Σ+ ground state have been measured at Doppler limited resolution in a dc discharge of hydrogen over magnesium. Most of the transitions arise from the fundamental bands of 24MgH and 24MgD, but, in addition, a few lines attributable to 25Mg and 26Mg species have been detected, as well as v=2←1 hot band transitions in 24MgH and 24MgD. Most of the lines are characterized by a doublet splitting due to the electron spin–rotation interaction (γN⋅S) which helps to distinguish them from the broader Rydberg transitions of atomic magnesium observed in the same spectral region. The spectra were analyzed in a combined fit with the FIR pure rotational transitions which leads to an accurate set of molecular parameters either for each vibrational level or as Dunham coefficients. The mass dependence of the molecular parameters is examined in terms of possible breakdown of the Born–Oppenheimer approximation.

Fourier transform infrared emission spectra of MgH and MgD

“…The available diode laser infrared spectra 27 contain lines from the vϭ1←0 and vϭ2←1 bands of MgH and MgD with an experimental uncertainty of 0.002 cm Ϫ1 , and there is no systematic discrepancy between those lines and our calibrated line positions. We included the diode laser infrared lines and all pure rotational lines 24 -26,28 in our data set.…”

“…To minimize the number of digits required to accurately reproduce the data, the fit to determine the constants of Tables I and II applied the sequential rounding and refitting procedure, 34 starting from the highest order parameter of the highest observed vibrational level. The new band constants for the vϭ0 levels of 24 MgH and 24 MgD are compared with the constants previously determined from the diode laser infrared 27 and pure rotational spectra, 26,28 in Table III. Note, however, that we have determined a set of band constants for the vϭ0 to 4 levels of 24 MgH and the vϭ0 to 5 levels of 24 MgD, while the previous diode laser infrared data included only the vϭ0 to 2 levels.…”

“…High resolution Fourier transform infrared emission spectra of MgH and MgD were recorded, and vibrationrotation transitions were observed in the X 2 ⌺ ϩ ground electronic state. The new data were combined with existing diode laser infrared 27 and pure rotational data, 24 -26,28 and spectroscopic constants were determined for vϭ0 to 4 of 24 MgH and vϭ0 to 5 of 24 MgD. In a combined fit of the six isotopomers, the Dunham constants and the Born-Oppenheimer breakdown correction parameters were obtained, and the equilibrium 24 Mg-H and 24 Mg-D bond distances were determined.…”

“…The pure rotational transitions of 24 MgH and 24 MgD were then identified in the far infrared spectral region. 24 -26 High resolution infrared spectra of MgH and MgD were obtained by Lemoine et al 27 using a diode laser infrared spectrometer, and lines from two vibration-rotation bands, vϭ1←0 and vϭ2←1, were identified. A few years later, some pure rotational lines of 24 MgH, 26 MgH, and 24 MgD were measured with very high accuracy in the millimeter-wave region.…”

Formation of the infrared emission lines of MG I in the solar atmosphere

“…The 7 and the 12 /mi lines were identified from theory as the 5g-6h, 6g-lh, and 6h-7i transitions of neutral magnesium (Chang & Noyes 1983). The identifications of the 12 /mi lines were confirmed by laboratory diode laser absorption spectroscopy (Lemoine, Demnynk, & Destombes 1988). Additional midinfrared lines of Mg i have also been noted in the solar spectrum (Chang & Noyes 1983;Chang 1987;Glenar et al 1988;Jefferies 1991) and confirmed in laboratory spectra (Lemoine et al 1990).…”