High Resolution Linelists for Strontium Monohydride (SrH) and Barium Monohydride (BaH)

Abstract

This work presents the first linelists for the diatomic alkaline earth-metal hydrides Strontium Hydride (SrH) and Barium Hydride (BaH). SrH and BaH have been of astronomical interest over the last century, and several attempts have been made to detect these hydrides in the spectra of sunspot umbrae. Both molecules have been studied by experimentalists, and numerous electronic systems have been identified. These linelists were generated using ab initio quantum chemistry techniques to produce potential energy curves, dipole moments, transition dipole moments, spin-orbit coupling, and electronic angular momentum curves. Ab initio calculations were performed in the quantum chemistry package MOLPRO using the MRCI method. These ab initio calculations were refined using experimentally collected wavenumbers for the electronic systems A2Π-X2Σ+, B2Σ+-X2Σ+, and E2Π-X2Σ+ for both SrH and BaH. The refinement was performed using the DUO software package which solves the rovibrational Schr¨odinger equation with couplings, following the ExoMol methodology for linelist creation. Both linelists feature models for the electronic states X2Σ+, A2Π, B2Σ+, and E2Π, which were fit between 0.005 and 0.02% of the available wavenumbers. Linelists for stable isotopologues of SrH (84SrH, 86SrH, 87SrH, and SrD) and BaH (134BaH, 135BaH, 136BaH, 137BaH, and BaD) have been generated and have been fit to experimental observations where available. The SrH linelist covers a wavenumber range of 7.14 to 32153 cm−1, with maximum vibrational coverage between V=15 and V=20 depending on state and rotational levels up to J=50.5. The BaH linelist covers a wavenumber range of 6.79 to 29055 cm−1, with vibrational coverage between V=20 and V=25 depending on state and rotational levels up to J=58.5. In total, these linelists represent around 11 million transitions for SrH and around 8 million transitions for BaH.

Date of Award	2024
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Maire Gorman (Supervisor) & Balazs Pinter (Supervisor)