Ground State Potential Energy Curve and Dissociation Energy of MgH

Abstract

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v''=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v''=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy.

Division Xii/Commission 14/Working Group on Molecular Data

“…During the reporting period papers on line lists, line strengths, and opacties have appeared. For metal hydrides, these studies include high-resolution spectra acquired with a Fourier transform spectrometer of bands in the A 2 Π − X 2 Σ + and B 2 Σ + − X 2 Σ + systems of 24 MgH (Shayesteh et al 2007) and of the E 2 Π − X 2 Σ + transition in CaH and CaD (Ram et al 2011b). The work on MgH provided the data on the highest lying vibrational level in the ground electronic state.…”

An extended Lennard-Jones potential energy function for diatomic molecules: Application to ground electronic states

“…The ground electronic states of 107 AgH (X 1 R þ ) [37], 35 24 MgH (X 2 R þ ) [44,45], Na 2 (X 1 R þ g ) [26], NaH (X 1 R þ ) [46], Na 39 K (X 1 R þ ) [27], 16 O 2 (X 3 R À g ) [47], and RbCs (X 1 R þ ) [48], sixteen in total, were investigated. The low-order molecular constants required for the calculation of the ELJ5/ELJ6 models are given in Table 1 for the 16 ground electronic states considered in this work.…”

SpS1-Laboratory spectroscopy of small molecules

“…Shayesteh et al (2003) completed a set of MgH observations in the infrared and visible that had led earlier in 2003 to the discovery of the linear MgH2 molecule. From the MgH B-X observations, Shayesteh et al (2007) determined all bound ground state levels with spectroscopic precision and obtained a very precise dissociation energy of 11104.7 cm −1 . The most important application of the spectroscopy of metal hydrides is in the classification of L-type dwarfs as discussed by Kirkpatrick (2005 Burrows et al (2005) for TiH (which has not been detected yet in L-dwarfs) by extrapolating laboratory observations and using line intensities based on ab initio calculations.…”