S. A. Marshall

Electron Spin Resonance Absorption Spectra of CO3− and CO33− Molecule—Ions in Irradiated Single‐Crystal Calcite

Single crystals of x‐ and γ‐irradiated calcite reveal a number of paramagnetic defect centers, two of which have been tentatively identified as the CO3− and CO33− molecule—ions. The ESR absorption spectrum of what is believed to be the CO3− molecule—ion is found to have symmetry about the calcite [111] direction with spin‐Hamilton parameters given by g‖=2.0051, g⊥=2.0162, A‖=13.1 Oe, and A⊥=9.4 Oe. The corresponding parameters for what is believed to be the CO33− molecule—ion which also exhibits symmetry about the crystal [111] direction are given by g‖=2.0013, g⊥ =2.0031, A‖=171.22 Oe, and A⊥=111.33 Oe. The parameters of these two spectra are discussed and compared with those reported for the isoelectronic NO3 and NO32− species. Optical measurements reveal two absorption bands, one at 6500 A and another at 4850 A. The longer‐wavelength band exhibits anisotropy and is found to have temperature‐dependent decay characteristics which are similar to those of the CO3− molecule—ion ESR spectrum. An activation e...

Electron Spin Resonance Absorption Spectrum of Y3+‐Stabilized CO33− Molecule–Ion in Single‐Crystal Calcite

An electron spin resonance absorption spectrum of effective spin S = 12 exhibiting two hyperfine structure doublet patterns has been observed in naturally occurring single crystals of calcite. The nuclei responsible for these doublets are identified from electron–nucleus double resonance and relative intensity measurements to be 89Y and 13C. From the mean of the spectroscopic splitting tensor values as well as from the 13C hyperfine structure separations, it is deduced that this spectrum is due to the CO33 − molecule–ion which is charge stabilized by a neighboring Y3+ ion. Experimental data suggest the existence of two sets of six equivalent centers each having an orthorhombic g tensor which is diagonal in a coordinate system whose z axis is canted with respect to the crystal [111] direction. The 89Y and 13C hyperfine tensors exhibit orthorhombic and axial symmetries, respectively, with the z axis of each being parallel to the crystal [111] direction. From an analysis of the 89Y hyperfine structure spectr...

ESR Absorption Spectra of Two Phosphorous Defect Centers in Irradiated Single‐Crystal Calcite

Two paramagnetic defect centers associated with phosphorous impurities and corresponding to S=½ and I=½ have been observed in irradiated single‐crystal calcite. One center, which is produced by γ irradiation, has an ESR absorption spectrum which consists of six doublets at 77°K and below, each exhibiting orthorhombic symmetry with spin‐Hamiltonian parameters given by gxx=2.0072, gyy=2.0033, gzz=2.0122, Axx=52.53 Mc/sec, Ayy=56.16 Mc/sec, and Azz=52.21 Mc/sec, where the relation between the x, y, z coordinates and those of calcite is discussed. As the temperature is raised, the lines of this spectrum are observed to broaden and at about 150°K the spectrum collapses into one doublet pattern which exhibits symmetry about the calcite (111) direction suggesting that the coordinates of the defect center undergo some form of motion whose mean z axis is parallel to the calcite (111) direction. This behavior is attributed to thermally induced reorientations of the defect between six magnetically inequivalent sites...

Motional Effects in the Electron Spin Resonance Absorption Spectrum of CO2– Molecule‐Ions in Single‐Crystal Calcite

The electron spin resonance absorption spectrum of CO2– molecule‐ion in single‐crystal calcite has been reinvestigated as a function of temperature. Between 77° and 250°K the spectrum exhibits orthorhombic symmetry and from the manner in which the widths of the spectral components behave, it is concluded that in this temperature range the CO2– molecule‐ion hops from one to another of three equivalent configurations each being rotationally displaced from the other two by  ± 2π / 3 radians in the (111) plane. Such hops involve the crossing of one of three equivalent potential wells whose depths are estimated to be 0.165 eV and whose widths are not more than 0.1 radians. At 250°K the spectrum associated with the (111) plane is wiped out. Above this temperature an axially symmetric spectrum appears whose parameters are simply related to those of the low‐temperature spectrum, and from the manner in which the widths depend upon temperature, it is concluded that in this temperature region the CO2– molecule‐ion u...

Electron Spin Resonance Absorption Spectrum of the AsO22− Molecule–Ion in γ‐Irradiated Single‐Crystal Calcite

An electron spin resonance absorption spectrum corresponding to S = 12, I = 32, and exhibiting orthorhombic symmetry has been observed in γ‐irradiated single‐crystal calcite. At 4.2°K, the spin‐Hamiltonian parameters are gzz = 2.0150, gxx = 1.9991, gyy = 1.9910, Azz = −152 MHz, Axx = 614 MHz, Ayy = −173 MHz, (gnβn/h) = −7.24 × 10−4MHz/Oe, e2qQ = 16.2 MHz, and η ≃ 0. The paramagnetic defect associated with this spectrum is identified as the AsO22− molecule–ion which is located at carbonate ion sites with its plane coincident with that of the carbonate ions. From the hyperfine structure splittings and the g‐tensor anisotropy, it is deduced that the unpaired electron has approximately 1% 4s, 96% 4p, and 3% 4d character and that it is almost completely localized on the arsenic atom.

Electron Spin Resonance Absorption Spectrum of CO2− Molecule Ions Associated with F− Ions in Single‐Crystal Calcite

Single crystals of calcite subjected to γ irradiation exhibit a number of paramagnetic defect centers. One of these has been identified as the CO2− molecule ion which is in close association with an F− impurity ion. An analysis of the ESR superhyperfine structure due to the fluorine nucleus suggests that for 3.3% of the time, negative charge is transferred from the F− ion to the CO2− molecule ion. This transfer of charge creates the diamagnetic CO22− molecule ion and atomic fluorine whose electron configuration is approximately 90% (2s22p5) and 10% (2s2p6). The effective magnetic field at the fluorine nucleus due to core polarization and 2s contact is calculated to be 21 kOe.

ELECTRON SPIN RESONANCE ABSORPTION SPECTRA OF HOLE-TRAP CENTERS ASSOCIATED WITH PHOSPHOROUS IN IRRADIATED SINGLE-CRYSTAL CALCITE.

An irradiation‐produced defect center associated with phosphorous impurities and corresponding to S = 12, I = 12 has been observed in natural single crystal calcite. Its electron spin resonance absorption spectrum consists of six doublets each exhibiting orthorhombic symmetry with spin‐Hamiltonian parameters given by gξξ = 2.0024, gηη = 2.0382, gζζ = 2.0090, Aξξ = − 17.25 MHz, Aηη = 14.27 MHz, and Aζζ = 17.33 MHz, where the coordinates ξ, η, and ζ are canted with respect to the calcite crystal coordinates. In addition to providing the nuclear magnetic moment of 31P, ENDOR data were used to determine the signs of the hyperfine splitting tensor components which in turn yield unambiguous values for the Fermi contact term and the traceless dipole–dipole interaction. On the basis of the small contact term in comparison to the dipole–dipole interaction strength and upon g‐value comparisons, it is proposed that the defect center is a CO3− molecule ion in close association with a PO23− molecule ion, probably mutu...

Shifts in the ESR Spectral Parameters of Atomic Hydrogen and Deuterium in Frozen Acids

The ESRspectra of atomic hydrogen and deuterium trapped in frozen acids has been reinvestigated in an effort to determine whether systematic shifts in the spectral parameters exist for this neutral S‐state atom. Following the example of Livingston, Zeldes, and Taylor, partially deuterated perchloric, phosphoric, and sulfuric acids were studied after γ irradiation at 77°K. Breit—Rabi expressions which take account of the nuclear quadrupole coupling energy were used in treating the data. This study discloses g‐value shifts of −0.00019, −0.00016, and −0.00012 and relative A‐value shifts of −0.94%, −0.61%, and −0.38% from the free‐gas values for the three acids, respectively. For perchloric and sulfuric acids, nuclear quadrupole coupling energies of 0.18 and 0.13 Mc/sec, respectively, were obtained. The possibility of 1s and 3dz 2 mixing in the hydrogen‐atom ground term due to crystalline electric fields is discussed.

Superhyperfine Interaction Due to 13C in the ESR Absorption Spectrum of Mn2+ in Single‐Crystal Calcite

The superhyperfine structure spectrum of Mn2+ interacting with 13C nuclei in single crystal calcite has been examined by electron spin resonance absorption spectroscopy at 77°K. An analysis of the spectrum performed in three mutually orthogonal planes of the calcite structure indicates that the core polarization of Mn2+ is 134 kOe.

Tentative identification by ESR of a CSO23− impurity radical in irradiated single-crystal calcite

Abstract A paramagnetic defect tentatively identified as CSO 2 3− has been studied in irradiated natural calcite. Identification is based on chemical considerations, the fact that more than 99% of sulfur nuclei have spin zero, and upon a g value calculation which involves no adjustment of model parameters to fit the experimental data. The center is produced by room-temperature electron, γ, or X-ray irradiation but may be seen by ESR only below about 190°K. The ESR spectrum shows no hyperfine structure and consists of contributions from six inequivalent sites. Pairs of these sites are nearly equivalent and the g -tensor principal axes are nearly such that one is along a normal CO direction, a second is perpendicular to a normal Ca0Ca plane, and the third is perpendicular to the other two. The associated g values are 2.001, 2.063, and 2.008, respectively.