Electron-spin resonance studies of the titanium cation (Ti+,3d3,4F) in rare gas matrices at 4 K: A crystal field interpretation

Abstract

Electron-spin resonance studies of laser-ablated titanium metal isolated in neon and argon display an intense feature which exhibits a symmetric, narrow line and a large matrix-dependent g shift. On the basis of a number of experiments, this is assigned to a matrix isolated 3d3,4F Ti+ ion in an octahedral matrix environment. Although the ground state of the gas-phase Ti+ ion is 3d24s1,4F, the assignment to the 3d3,4F state is supported by the small hyperfine structure which is observed. The neon magnetic parameters are: g=1.934(1) and A(47Ti)=64(1) MHz; for argon, g=1.972(1) and A=56(1) MHz. This unusual stabilization of an excited atomic state by a rare gas matrix is consistent with ab initio studies, and has been previously found for atomic nickel. A crystal-field study of the expected behavior of a d3,4F ion isolated in a tetrahedral, octahedral, or cuboctahedral environment supports the assignment to an octahedral Ti+(Rg)6 species, and using the atomic spin–orbit parameter, ζ permits accurate values of Dq to be derived from the measured g values. Finally, it is also noted that for small values of Dq/(Dq+ζ), or for a d3,4F ion in a tetrahedral environment, an as yet unobserved, unequal Zeeman splitting of the fourfold degeneracy occurs, causing a departure of the Zeeman energies from the standard formula of EZeeman=βeH0gM, with M=±3/2, ±1/2. For these situations it becomes necessary to define two values of g, corresponding to the more strongly (g3/2) and less strongly (g1/2) affected Zeeman levels, respectively.