ESR of chromium metal atoms and molecules in matrices

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.

Spin trapping by bis(benzene)chromium: A density functional study

“…Nevertheless, we have checked the reliability of this basis set by carrying out, in analogy with the procedure used for the tuning of the EPR basis sets, 7 some hcc calculations for the isolated chromium atom in its fundamental state ( 7 S). The obtained value (À32.6 G) is very close to the experimentaly one (33 G), 26 thus proving that the Wachters basis set could provide reliable magnetic properties for chromium compounds. Isotropic hyperfine coupling constants are related to the spin densities at the corresponding nuclei by: 27…”

V, Nb, and Ta hydride molecules in deuterium and rare-gas matrices: Infrared and electron spin resonance spectra

“…25 After a reasonable fit was made using only xy 1 and xy 3 ͑with QЈϭ0͒, the beginning of the pattern was assigned to the lowest ⌬M I ϭ0 line and A ʈ , QЈ, and g ʈ were varied until a reasonable fit was again made. ⌬M I ϭ0, Ϯ1, Ϯ2 lines are included in Table IV and do account for many of the lines.…”

Electron Spin Resonance of the H···NH2 Radical Pair

“…The Heli-tran, X-band ESR spectrometer, and deposition equipment have been previously described. 14 The new feature in these experiments is a corona discharge unit, 11 operating at ∼3 KV, through which only pure rare gas was passed. The rare-gas ammonia mixture was passed into the vacuum system in parallel with the corona discharge in nearly equal amounts so that both gas flows were condensed simultaneously on the copper surface at 4 K. Normal ammonia (Matheson, 99.99% purity), isotopically enriched 15 NH 3 (Cambridge Isotopes, Inc., 99% enrichment, 98+% purity), and deuterated ammonia (Cambridge, 99% enrichment, 98+% purity) were diluted to ∼5% with neon (Matheson, 99.9995% purity), argon (Airco, 99.999% purity), or krypton (Matheson 99.999% purity).…”