The $X^{1}\Sigma ^{+}_{g}$X1Σg+ ground state of Mg2 studied by Fourier-transform spectroscopy

Abstract

The A(1)Σu(+) - X(1)Σg(+) UV spectrum of Mg2 has been investigated with high resolution Fourier-transform spectroscopy. Mg2 vapor was created in a heat pipe. Various spectroscopic methods have been employed, such as conventional absorption spectroscopy with light from a broad band lamp and laser-induced fluorescence. The high resolution of the Fourier-transform spectrometer, together with computer aided evaluation methods of the spectra, yields precise transition frequencies. The new data and data available from earlier investigations are applied in direct potential fits of lower and upper electronic states. Various representations of potential energy curves for the ground state X(1)Σg(+) have been employed and their benefits in terms of smallest number of parameters are discussed. Scattering lengths are derived for the homonuclear isotopologues and compared with previous results.

Quantum computation solves a half-century-old enigma: Elusive vibrational states of magnesium dimer found

“…Four decades later, in an effort to characterize states with v″ > 13, Knöckel et al (20,21) examined the A 1 Σ u + → X 1 Σ g + transition using laser-induced fluorescence (LIF), repeating and refining the earlier LIF experiment by Scheingraber and Vidal (22). They improved and expanded the original 24 Mg 2 dataset of Balfour and Douglas by reporting a total of 333 G(v″, J″) and 1,351 G(v′, J′) rovibrational term values involving v″ = 0 to 13 and v′ = 1 to 46, respectively, and constructed a few experimentally derived analytical forms of the X 1 Σ g + PEC, extrapolated to the asymptotic region using the theoretical C 6 (23), C 8 (24), and C 10 (24) coefficients, which support the discrete spectral data in the 3.27 to 8.33 Å range (20). Although these refined PECs supported 19 24 Mg 2 vibrational levels, reinforcing the initial prediction of Li and Stwalley (17), Knöckel et al (20) were unable to identify A 1 Σ u + (v′, J′) → X 1 Σ g + (v″, J″) transitions involving the elusive high-lying vibrational levels with v″ > 13 in their LIF spectra.…”

“…Typically, high-lying vibrational states near dissociation constitute a small fraction of the entire vibrational manifold, but this is not the case for the weakly bound magnesium dimer, which has a shallow minimum on the ground-state PEC at r e = 3.89039 Å (20) and a tiny dissociation energy D e of 430.472(500) cm −1 (20,21). If the five extra levels, which have been speculated about, truly existed, they would represent more than a quarter of the entire vibrational manifold in the ground electronic state.…”

“…It is intriguing why a seemingly docile main group diatomic continues to challenge stateof-the-art spectroscopic techniques. The experimental difficulties in detecting the elusive v″ > 13 states of the magnesium dimer originate from several factors, including small energy gaps between high-lying vibrations that are comparable to rotational spacings (12,25), resulting in overlapping spectral lines, and unfavorable signal-to-noise ratio in the existing LIF spectra (20). Rotational effects complicate the situation even more, since, in addition to affecting line intensities (20,22,25), they may render the high-lying vibrational states of Mg 2 unbound.…”

“…The experimental difficulties in detecting the elusive v″ > 13 states of the magnesium dimer originate from several factors, including small energy gaps between high-lying vibrations that are comparable to rotational spacings (12,25), resulting in overlapping spectral lines, and unfavorable signal-to-noise ratio in the existing LIF spectra (20). Rotational effects complicate the situation even more, since, in addition to affecting line intensities (20,22,25), they may render the high-lying vibrational states of Mg 2 unbound. All of these and similar difficulties prompted Knöckel et al (20,21) to conclude that experimental work alone is insufficient and that accurate theoretical calculations are needed to guide further analysis of the ground-state PEC and rovibrational states of Mg 2 , especially the elusive v″ > 13 levels near the dissociation threshold.…”

<i>Ab initio</i> electronic structure of the Sr₂⁺ molecular ion

“…Both approaches may be used for the formation of the Sr + 2 molecular ion studied in this paper. Neutral alkaline-earth dimers have been spectroscopically studied in a number of experiments, including Be 2 [47,48], Mg 2 [49][50][51], Ca 2 [52][53][54][55][56], Sr 2 [57][58][59][60][61], Ba 2 [62,63]. They also received considerable attention as the subject of theoretical studies , including several works on Sr 2 [90][91][92][93][94][95][96][97].…”