Helium hydride molecule

Protonation of a helium atom gives He-H+, the helium hydride cation, the simplest heteronuclear molecule [60]. Conceptually, of course, this can also be formed by the union of a helium dication and a hydride ion, or a helium cation and a hydrogen atom ... 

From the most recent calculations, it appears probable that the helium hydride ion (HeH)+ is a stable species with dissociation energy between 1 75 and 2 05 eV. Use the method of the discussion at the beginning of this chapter to show why this ion might be a stable species whereas the neutral HeH molecule would not. 

Thus the hydrogen atom, with one electron, can achieve the helium structure by taking up another electron, to form the hydride anion, H , as in the salt lithium hydride, Li+H . But the hydrogen atom can also achieve the helium structure by sharing its electron with the electron of another hydrogen atom, to form a shared-electron-pair bond. Each of the two atoms thus contributes one electron to the shared electron pair. The shared electron pair is to be counted first for one hydrogen atom, and then for the other if this is done, it is seen that in the hydrogen molecule each of the atoms has the helium structure ... 

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