K. J. Zeringue

Electron spin resonance of the C6, C8, and C10 molecules

Electron‐spin‐resonance (ESR) signals attributed to the linear C6, C8, and C10 molecules in their lowest 3Σ states, presumably their ground states, have been observed in solid neon and argon matrices at 4 K. There is evidence of two forms of the C10 molecule, perhaps indicating two slightly bent structural isomers. Laser vaporization of graphite and 13C‐enriched graphite produced a high proportion of these larger molecules. Hyperfine interaction in the 13Cn molecules was small and resolved only for C6, indicating cumulene‐type bonding with the unpaired spins in pπ orbitals, as in C4. The zero‐field‐splitting parameters ‖D‖ were found to be 0.363, 0.783, and 0.190 cm−1, respectively, in solid neon. The increase in ‖D‖ through C8 is attributed to a corresponding variation in the spin–orbit coupling with low‐lying states, principally the 1Σ+g, as the chains lengthen. Gross orbital spin populations and 1Σ+g– X 3Σ−g energy differences were obtained from Hartree–Fock calculations in order to interpret the hfs a...

Magnetic circular dichroism studies of matrix‐isolated atoms: Excited state spin‐orbit coupling constant reduction of copper in the noble gases

The absorption and magnetic circular dichroism spectra of the 2P←2S transition of matrix‐isolated copper atoms have been measured in krypton and xenon matrices. A dramatic reversal in the MCD C term pattern is observed. From a spectral band moment analysis it is shown that: (1) noncubic lattice cage vibrational motions are more important than cubic ones in contributing to the observed bandwidths and (2) the Cu excited state spin‐orbit coupling constant (λ) in krypton is reduced to 57% of its gas phase value, whereas in xenon it is reduced to −14% of its gas phase value. Calculations using the Moran model show that the excited state geometry of the metal/rare gas cage is distorted via the Jahn–Teller effect in opposite ways in krypton and xenon matrices. The negative sign of λ in xenon reveals a reversal in the order of the 2P state spin‐orbit multiplets. Neither this reversal nor the reduction of λ in krypton can be accounted for by the Jahn–Teller effect. We attribute the spin‐orbit constant reduction to...

Ground-state exchange energy of the Mn2 antiferromagnetic molecule

Abstract Peculiar transitions in the optical spectra of Mn atoms isolated in argon matrices confirm the existence of Mn 2 molecule. The temperature variation of the absorption and MCD intensity in the range 13-27 K demonstrate that the Mn 2 molecule is antiferromagnetic and allows a precise determination of its ground-state exchange energy: J = −10.3 ± 0.6 cm −1 .

Atom–matrix interactions: An MCD study of copper atoms in argon

The absorption and MCD spectra of the 2P ← 2S transition of Cu atoms isolated in argon matrices have been measured over the temperature range 13–25 K. Spectral band moments (up to third order in MCD) have been determined and parameters of interest extracted from them. The observed triplet bands’ separation and MCD C term signs are analyzed assuming a static trigonal site distortion. It is shown that a static site distortion model is incapable of reproducing the experimental results. Simultaneous spin orbit and noncubic lattice vibrational couplings (Jahn–Teller effect) are shown to be active in the Cu excited 2P state. The observed triplet of bands and its MCD C terms are satisfactorily described by an adiabatic model developed by Moran. Comparison of the observed band shape to ones calculated by Cho using Monte Carlo methods show that simultaneous spin‐orbit and e and t2 lattice mode interactions are operative. The observed reduction of 25% in the excited state spin‐orbit coupling constant is attributed ...

The ground state and zero‐field splitting of the GdO molecule

The X‐band ESR spectrum of GdO was obtained in an argon matrix at 4 °K as a series of 16 fine‐structure lines between 0 and 12 000 G. Analysis proved that most of these lines were due to off‐principal‐axis transitions and established the ground state as 9Σ. An accurate fit to the data required the inclusion of a small b40 term (quartic in Sz) besides the usual b20 = D term in the spin Hamiltonian. The derived parameters in an argon matrix are g∥ = 1.990(9), g⊥ = 1.986(5), ‖ b20 ‖ = ‖ D ‖ = 0.2078(3) cm−1, and ‖ b40 ‖ = 0.000 40(5) cm−1. The two strongest lines were also observed in a neon matrix.

ESR of GdF3 and related molecules at 4 °K

The pyramidal (C3v) GdF3 molecule was trapped in neon and argon matrices at 4°K and its ESR spectrum measured in the X‐band region. In neon the spectrum exhibited several off‐principal‐axis transitions which were sensitive to the assigned magnetic parameters. It was shown to be a S = 7/2 molecule (ground state 8A1) with g∥ = 1.995, g⊥ = 1.990, and ‖ D ‖ = 0.433 cm−1. The 19F hfs was unresolved and therefore <∼10 G. Only the mS = +1/2 ↔ −1/2 transition of GdH3 was observed, yielding ‖ D ‖ = 0.7 to 1.3 cm−1, and it is inferred to be a planar (D3h) molecule (ground state 8A1′). Weak spectra of GdCl3 (8A1) and GdF2 (9A1) were also observed, yielding ‖ D ‖?0.36 and 0.20 cm−1, respectively.