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

Abstract

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, (H2)CrH, CrH2, (H2)CrH2, and (H2)2CrH2 are identified by isotopic substitution (D2, HD, and H2+D2) and comparison with DFT (density functional theory) and MP2 calculations of vibrational fundamentals. The (H2)CrH complex with lower energy than CrH3 is trapped and no band is observed for CrH3. Reactions with H2 and D2 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 [CrH4]* intermediate in the formation of (H2)CrH2. The major bands at 1529.5 cm-1 for H2 and 1112.2 cm-1 for D2 in neon and at 1521.3 cm-1 in pure hydrogen and 1106.9 cm-1 in pure deuterium are due to (H2)2CrH2 and (D2)2CrD2, respectively, which is the most stable form for chromium hexahydride.