EPR Studies of Ti3+–H+Centers in X‐Irradiated α‐Quartz

Experimental Determination of a Single Atom Ground State Orbital through Hyperfine Anisotropy

Historically, electron spin resonance (ESR) has provided excellent insight into the electronic, magnetic, and chemical structure of samples hosting spin centers. In particular, the hyperfine interaction between the electron and the nuclear spins yields valuable structural information about these centers. In recent years, the combination of ESR and scanning tunneling microscopy (ESR-STM) has allowed to acquire such information about individual spin centers of magnetic atoms bound atop a surface, while additionally providing spatial information about the binding site. Here, we conduct a full angle-dependent investigation of the hyperfine splitting for individual hydrogenated titanium atoms on MgO/Ag(001) by measurements in a vector magnetic field. We observe strong anisotropy in both the g factor and the hyperfine tensor. Combining the results of the hyperfine splitting with the symmetry properties of the binding site obtained from STM images and a basic point charge model allows us to predict the shape of the electronic ground state configuration of the titanium atom. Relying on experimental values only, this method paves the way for a new protocol for electronic structure analysis for spin centers on surfaces.

Some properties of Ti-related paramagnetic centres relevant for electron spin resonance dating of single sedimentary quartz grains

We performed Q-band ESR spectroscopy on several single quartz grains from different geological deposits. Various properties of Ti-related impurity centres in quartz relevant for ESR dating were studied. It will be shown that some properties, such as sensitivity change and response to artificial gamma-irradiation, may vary from grain to grain. It is concluded that single grain ESR dating is feasible at a pure experimental level.

Bleaching of ESR signals by the sunlight: a laboratory experiment for establishing the ESR dating of sediments

A laboratory bleaching experiment was performed in order to improve the method of ESR dating of sediments. Several sedimentary, volcanic, and granitic quartz samples showed consistent bleaching response for the exposure to halogen lamps. It was found that the most sensitive signals are the Ti-H and Ti-Na centers. There was no difference observed within the samples exposed to light filtered by several color glass plates, according to the present preliminary result.

Large-magnitude high-spin nuclear parameters in a Ti3+ center from X-band EPR measurements at 10 K

Precise 10 K X-band EPR measurements and subsequent spin-Hamiltonian analysis by direct matrix diagonalization methods are reported for a Ti3+ (S = 1/2) center in tetragonal zircon (zirconium silicate, ZrSiO4). A special, and previously unobserved, feature of the supposedly uniaxial spectrum is the marked angular dependence of the titanium hyperfine lines in the perpendicular, ab crystal plane. As discussed, this can only arise from the presence of high-spin nuclear terms of dimension BIk, SIk (k = 3, 5) in the spin Hamiltonian. Parameters arising from these terms were determined to have magnitudes very much larger than observed previously in first-row transition ions. The consequences of precise determination of these high-spin parameters are significant and several: a precise determination of the nuclear quadrupole tensor leading to a ratio 47P/49P in excellent agreement with the ratio derived from the corresponding nuclear quadrupole moments; an apparent anisotropy in the nuclear Zeeman interaction which can be identified with anisotropy in the chemical shielding "tensor"; a marked hyperfine anomaly. The origin and significance of these observations are discussed.