Metal Dihydride (MH₂) and Dimer (M₂H₄) Structures in Solid Argon, Neon, and Hydrogen (M = Ca, Sr, and Ba):  Infrared Spectra and Theoretical Calculations

Laser-ablated Ca, Sr, and Ba atoms were co-deposited with H 2 in excess argon, neon, and hydrogen to form alkaline-earth metal hydrides. The metal dihydrides (CaH 2, SrH 2, and BaH 2 ) were identified in solid argon, neon, and hydrogen. Increasing infrared intensity in the symmetric stretching mode and electronic structure calculations show that these dihydride molecules have decreasing obtuse valence angles, respectively. These MH 2 molecules also form (H 2 ) n MH 2 complexes. Further dimerization of metal dihydrides gave double-bridged HCaH 2 CaH with D 2 h symmetry and triple-bridged HSrH 3 Sr and HBaH 3 Ba with C 3 v symmetry, which are confirmed by D 2 and HD isotopic substitutions and quantum chemical calculations. Bonding in heavy alkaline metal hydrides is discussed.