Beryllium monohydride (BeH): Where we are now, after 86years of spectroscopy

• Published in: Journal of molecular spectroscopy 2015-05, Vol.311, p.76-83
• Main Author: Dattani, Nikesh S.
• Format: Article
• Language: English
• Subjects: Big Bang physics; Cool stars; Dispersion constants; Early universe chemistry; Exoplanet atmosphere; Fundamental molecules; Halo nucleonic molecules; Interstellar chemistry & astrochemistry; Isotope effect; Potentiology & potential energy curves and surfaces; Stellar chemistry and the Sun; Theory vs experiment; Ultra-high precision
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2014.09.005

[Display omitted] •Extensive review of experimental and theoretical work on BeH including 138 key references•Most accurate empirical potentials for Be(H, D, &T) to date, using the MLR model•Comparison between the best current ab initio & empirical energy spacings for Be(H, D & T)•Comparison of spectroscopic constants, Born–Oppenheimer corrections, for Be(H, D & T)•New Van der Waals dispersion constants with finite-mass corrections for Be(H, D & BeT) BeH is one of the most important benchmark systems for ab initio methods and for studying Born–Oppenheimer breakdown. However the best empirical potential and best ab initio potential for the ground electronic state to date give drastically different predictions in the long-range region between where the highest measurements have been made, and the dissociation energy; a region which is about ∼1000cm−1 for 9BeH, ∼3000cm−1 for 9BeD, and ∼13000cm−1 for 9BeT. Improved empirical potentials and Born–Oppenheimer breakdown corrections have now been built in this work for the ground electronic states X(12Σ+) of all three isotopologues. The predicted dissociation energy for 9BeH from the new empirical potential is now in agreement with the current best ab initio prediction in all 5 digits of the former’s precision, while the previous best empirical potential was in disagreement by 74cm−1. The previous best empirical potential predicted the existence of unobserved vibrational levels for all three isotopologues, and the current best ab initio study also predicted the existence of all of these levels, and 7 more in total. With the exception of two, the present empirical potential agrees with the existence of all of the ab initio potentials’ extra levels not predicted by the earlier empirical potential. With one exception, all energy spacings between vibrational energy levels for which measurements have been made, are predicted with an agreement of better than 1cm−1 between the new empirical potential and the current best ab initio potential, but some predictions for unobserved levels are still in great disagreement, and the equilibrium bond lengths are different by orders of magnitude.