Infrared Spectra of Gallium Hydrides in Solid Hydrogen:  GaH₁,₂,₃, Ga₂H₂,₄,₆, and the GaH₂,₄⁻ Anions

Reactions of laser-ablated Ga atoms and normal hydrogen during co-deposition at 3.5 K give GaH as the major product and GaH 2, GaH 3, GaH 2 -, GaH 4 -, and Ga 2 H 2 as minor products. Identifications are based on infrared spectra, isotopic substitution (D 2, H 2 + D 2 mixtures, HD), comparisons to earlier work, and frequencies calculated by density functional theory. Mercury arc radiation destroyed the GaH 2 - and GaH 4 - anions, decreased GaH and increased GaH 3, destroyed Ga 2 H 2, and produced new bands due to Ga 2 H 4, two Ga 2 H 5 radical isomers, and Ga 2 H 6 . ArF laser irradiation at 193 nm was particularly effective in converting GaH to GaH 3 and to Ga 2 H 6 . The GaH 4 - anion absorptions in solid hydrogen are compatible with solid NaGaH 4 bands: Near-ultraviolet excitation of GaD 2 - with D 2 present increases GaD 4 - absorptions. Warming these samples to remove the H 2 matrix replaced sharp gallium hydride molecular absorptions with broad 1800−2000, 1300−1700, and 600−700 cm -1 bands due to higher oligomers containing terminal and bridged Ga−H bonds.