Beryllium monohydride (BeH) is an example of a molecule with a half-bond order according to
molecular orbital theory
In chemistry, molecular orbital theory (MO theory or MOT) is a method for describing the electronic structure of molecules using quantum mechanics. It was proposed early in the 20th century.
In molecular orbital theory, electrons in a molecul ...
. It is a
metastable
In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...
monoradical species which has only been observed in the gas phase. In
beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...
monohydride, beryllium has a
valency of one, and
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
has a valency of one.
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 the Sun. Because of the long lifetime (by nuclear physics standards) of
11Be,
11BeH is the leading candidate for the formation of the first
halo nucleonic molecule.
BeH has been studied spectroscopically since 1928 and in over 80 theoretical studies (see
for a review).
The bond length is 134.2396(3) pm
and the dissociation energy is 17702(200) cm
−1.
The dimeric molecule Be
2H
2 has also been observed in an argon matrix at 10 K
[.]
References
Beryllium compounds
Metal hydrides
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