Infrared Spectra of Rhodium Hydrides in Solid Argon, Neon, and Deuterium with Supporting Density Functional Calculations

Abstract

Laser-ablated Rh atoms react with H 2 to give RhH 2 and RhH as primary products, which are trapped or react with additional hydrogen in the condensing solid argon, neon, and deuterium matrixes. RhH gives a major 1920.6 cm - 1 band in argon, a minor 1935.5 cm - 1 band in neon, and no absorption in deuterium. RhH 2 produces sharp 2099.4 and 2053.4 cm - 1 and 2099.7 and 2052.2 cm - 1 bands in solid argon and neon, respectively and no absorption in deuterium; these absorptions increase on annealing the matrix to allow diffusion, which shows that ground state Rh inserts spontaneously into H 2 . Additional absorptions at 2122.4 and 2078.2 cm - 1 (1527.3 and 1494.4 cm - 1 with D 2 ) in neon and at 1521.1 and 1496.1 cm - 1 in deuterium are assigned to the higher hydride complexes (H 2 )RhH 3 and (H 2 )RhH 2 , respectively. A weaker 737.6 cm - 1 absorption in neon is due to the side-bound complex Rh(H 2 ) 2 . Both (D 2 )RhH 2 and Rh(H 2 )(D 2 ) rearrange H and D on photoexcitation suggesting a tetrahedral transition state. Rhombic (RhH) 2 is observed in all three matrix systems. These assignments are supported by D 2 , HD, and H 2 + D 2 substitution and density functional theory frequency and structure calculations.