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

摘要

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)_2CrH_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)_2CrH_2 and (D_2)_2CrD_2, respectively, which is the most stable form for chromium hexahydride.