Chromium Hydrides and Dihydrogen Complexes in Solid Neon, Argon, and Hydrogen: Matrix Infrared Spectra and Quantum Chemical Calculations

Reactions of chromium atoms with molecular hydrogen are investigated through matrix-isolation infrared spectroscopy of products and complexes. Laser-ablated chromium atoms react with molecular hydrogen upon condensation in excess neon and argon and in pure hydrogen. The reaction products, CrH, (H 2 )CrH, CrH 2, (H 2 )CrH 2, and (H 2 ) 2 CrH 2 are identified by isotopic substitution (D 2, HD, and H 2 +D 2 ) and comparison with DFT (density functional theory) and MP2 calculations of vibrational fundamentals. The (H 2 )CrH complex with lower energy than CrH 3 is trapped and no band is observed for CrH 3 . Reactions with H 2 and D 2 mixtures and with HD give different relative yields of the same mixed isotopic bands, which shows that exchange of dihydride and dihydrogen complex positions occurs in the energized [CrH 4 ]* intermediate in the formation of (H 2 )CrH 2 . The major bands at 1529.5 cm -1 for H 2 and 1112.2 cm -1 for D 2 in neon and at 1521.3 cm -1 in pure hydrogen and 1106.9 cm -1 in pure deuterium are due to (H 2 ) 2 CrH 2 and (D 2 ) 2 CrD 2, respectively, which is the most stable form for chromium hexahydride.