Identification of the (H-)(H2)12 Hydride Anion Cluster in Solid Hydrogen

Pulsed-laser ablation of metals with normal hydrogen [deuterium] condensing at 3.5 K produces a strong 3972.0 [2869.8] cm -1 absorption the same as high energy irradiation of solid hydrogen [deuterium]. New experimental observations and quantum chemical calculations show that these charge centers are (H - )(H 2 ) n [(D - )(D 2 ) n ] anion clusters, which have not been observed in the gas phase and are unique to solid hydrogen. First, doping our H 2 [D 2 ] samples with CCl 4, a very efficient electron scavenger, replaces the above absorptions with new 4067.0 [2925.6] cm -1 bands, which are due to the (Cl - )(H 2 ) n [(Cl - )(D 2 ) n ] anion clusters. Second, (H - )(H 2 ) n is destroyed by λ > 290 nm but restored with 193 nm radiation through photoionization of metal atoms to produce electrons for capture by H atoms. Third, model MP2 calculations for (H - )(H 2 ) 6 with the D 6 h structure, which is a contracted portion of the solid hydrogen lattice, strongly supports these new assignments and suggests that the complex has the same coordination number 12 as the hydrogen lattice. Thus, (H - )(H 2 ) 12 cluster anions are characterized in the solid hydrogen microcrystal.