ESR of chromium metal atoms and molecules in matrices

Publisher Website
Google Scholar
Abstract
Chromium metal, natural and isotopically enriched in 53Cr (I=3/2), was vaporized and trapped in solid neon, argon, and krypton at 4 K. An extensive ESR spectrum of 16 lines between 200 and 7000 G in neon and argon matrices was found to be due to an axial molecule with S=3, ‖D‖=0.110 cm−1, g⊥=1.9970, g∥=1.9996. 53Cr spectra showed essentially isotropic hyperfine interaction of the six unpaired spins with apparently only one nucleus and an accompanying electric field gradient at that nucleus. It is concluded that the molecule is a trigonally distorted tetrahedral Cr4 or possibly a square-based pyramidal Cr5. The unique apical atom is bonded relatively weakly to the ‘‘base’’ and is the locus of almost all of the s character among the unpaired spins. In argon and krypton matrices, another species with S=3 is observed near g=2.0 but with only a small zero-field splitting (‖D‖=0.0049 cm−1, g∥=2.005, g⊥=2.0015 in argon). The possibilities of it being a weakly perturbed Cr atom in an asymmetrical matrix site or a Crn molecule, where n(≥3) is the number of equivalent atoms, are discussed.

This publication has 26 references indexed in Scilit: