Beryllium monohydride

Beryllium monohydride (BeH) is an example of a molecule with a half-bond order according to molecular orbital theory. It is a metastable monoradical species which has only been observed in the gas phase. In beryllium monohydride, beryllium has a valency of one, and hydrogen has a valency of one.

Beryllium monohydride

Identifiers
CAS Number	13597-97-2
3D model (JSmol)	Interactive image
ChemSpider	21865051
InChI InChI=1S/Be.H Key: AYBCUKQQDUJLQN-UHFFFAOYSA-N
SMILES [BeH]
Properties
Chemical formula	BeH^•
Molar mass	10.02012 g mol^−1
Appearance	Colourless gas
Thermochemistry
Std molar entropy (S^o298)	176.83 J K^−1 mol^−1
Std enthalpy of formation (ΔfH^⦵298)	321.20 kJ mol^−1
Hazards
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 0.002 mg/m^3 C 0.005 mg/m^3 (30 minutes), with a maximum peak of 0.025 mg/m^3 (as Be)[1]
REL (Recommended)	Ca C 0.0005 mg/m^3 (as Be)[1]
IDLH (Immediate danger)	Ca [4 mg/m^3 (as Be)][1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

BeH has only 5 electrons and is the simplest open shell neutral molecule, and is therefore extremely important for the benchmarking of ab initio methods. With such a light mass, it is also an important benchmark system for studying the breakdown of the Born-Oppenheimer approximation. Due to its simplicity, BeH is expected to be present in astronomical contexts such as exoplanetary atmospheres, cool stars, and the interstellar medium, but so far has only been found on our Sun.[2] Because of the long lifetime of ¹¹Be, ¹¹BeH is the leading candidate for the formation of the first halo nucleonic molecule.[3]

BeH has been studied spectroscopically since 1928 and in over 80 theoretical studies (see [3] for a review).

The bond length is 134.2396(3) pm [3] and the dissociation energy is 17702(200) cm⁻¹.[3]

The dimeric molecule Be₂H₂ has also been observed in an argon matrix at 10 K[4]

References

1. NIOSH Pocket Guide to Chemical Hazards. "#0054". National Institute for Occupational Safety and Health (NIOSH).
2. Dattani, Nikesh S. (2015). "Beryllium monohydride (BeH): Where we are now, after 86years of spectroscopy". Journal of Molecular Spectroscopy. 311: 76–83. arXiv:1408.3301. Bibcode:2015JMoSp.311...76D. doi:10.1016/j.jms.2014.09.005. S2CID 118542048.
3. Dattani, Nikesh S. (2015). "Beryllium monohydride (BeH): Where we are now, after 86 years of spectroscopy". Journal of Molecular Spectroscopy. 311: 76–83. arXiv:1408.3301. Bibcode:2015JMoSp.311...76D. doi:10.1016/j.jms.2014.09.005. S2CID 118542048.
4. Thomas J. Tague Jr., Lester Andrews (1993). "Reactions of beryllium atoms with hydrogen. Matrix infrared spectra of novel product molecules". J. Am. Chem. Soc. 115 (25). pp. 12111–12116. doi:10.1021/ja00078a057..