Dibridged, Monobridged, Vinylidene-Like, and Linear Structures for the Alkaline Earth Dihydrides BeH, MgH, CaH, SrH, and BaH. Proposals for Observations.

This research reports a search for peculiar monobridged structures of the EH molecules (E = Be, Mg, Ca, Sr, Ba). For BeH and MgH, the monobridged geometry is not an equilibrium but rather a transition state between the vinylidene-like structure and the global minimum HE-EH linear geometry. However, for CaH, SrH, and BaH, this situation changes significantly; the linear structure is no longer the global minimum but lies higher in energy than two other equilibria, the dibridged and monobridged structures. The planar dibridged structures of both SrH and BaH should be observable via IR spectroscopy. Although the remarkable monobridged structures lie 8.3 (Sr) and 7.6 kcal/mol (Ba) higher, the large IR intensities of the terminal E-H stretching frequencies may make the monobridged structures observable. The monobridged structures have sizable permanent dipole moments (3.07 and 3.06 D for Sr and Ba, respectively) and also should be observable via microwave spectroscopy.