E.S.R. of Cl17O2

The E.S.R. spectrum of ¹⁷O-labelled ClO₂ was studied in an X-irradiated single crystal of KClO₃ and in toluene solution. The isotropic hyperfine constant measured in solution is 12·0 gauss and allows the correct choice of signs to be made in analysing the dipolar tensor in the solid. The values of the anisotropic tensor indicate a spin density of 0·27 on each oxygen.     

0+ states and E0 and E2 transition rates in even Sn nuclei

0⁺ states and their depopulating E0 and E2 transitions have been studied in ^112–124Sn. Several methods of γ-ray and electron spectrometry have been employed, including special coincidence techniques for lifetime, conversion electron and double Coulomb excitation measurements. For ^114–118Sn the E2 transition probabilities from the first excited 0⁺states (0₂⁺) are about 20 W.u., which is compatible with a vibrational two-phonon character. Also the E0 transition probabilities from these states are within a factor of two from the vibrational values. For the second excited 0⁺ states (0₃⁺) the corresponding E2 and E0 transition probabilities are considerably smaller. A total of 12 E0 transitions have been observed. The 0₃⁺ → 0₂⁺ transition is observed in ^114–120Sn and has in ¹¹⁶Sn a reduced transition probability 1–2 orders of magnitude larger than those of the groundstate E0 transitions, which indicates that the 0₃⁺ and 0₂⁺ states are strong mixtures of components with different 〈r²〉. The 0⁺ states in ¹¹⁶Sn are discussed as possible rotational band heads associated with a deformation β₂ ≈ 0.2. The Coulomb excitation cross section of the 0₂⁺ state is found to be sensitive to an interference term including matrix elements with the 2₂⁺ state. The relative sign of this term has been determined.     

An E.S.R. study of the triplet dianions of 1,3,5-triphenylbenzene and 2,4,6-triphenyl-sym-triazine

Upon prolonged alkali reduction in ethereal solvents 1,3,5-triphenylbenzene (Tpb), 2,4,6-triphenyl-sym-triazine (Tpt) and 2,4,6-tritolyl-sym-triazine (Ttt) can be reduced to their dinegative ions. Dissolved in rigid solvent matrices these ions produce E.S.R. spectra which are characteristic for randomly oriented triplet systems. Hückel and SCF MO calculations indicate that these dianions have a twofold degenerate lowest anti-bonding level.

Although the ions Tpb^2- and Tpt^2- are iso-electronic their magnetic properties prove to be strikingly different. While Tpb^2- has a triplet ground state irrespective of solvent, counter ion and temperature, Tpt^2- (and also Ttt^2-) has a singlet ground state with a thermally accessible triplet state in solvents with poorly solvating properties and has a triplet ground state in better solvating media. Furthermore, the zero field splitting parameters D and E of the lowest triplet states of Tpt^2- and Ttt^2- are markedly different from those obtained from Tpb^2-. The former show a considerably larger D value than Tpb^2- and, in contrast to Tpb^2-, the ions Tpt^2- and Ttt^2- have a non-zero E value in poorly solvating solvents, pointing to a non-trigonal spin distribution of the triplet systems.

An explanation of the observed differences is given in terms of current MO theories. The results suggest that in the case of Tpt^2- and Ttt^2- the association with the counter ions even in strongly solvating solvents is very strong.     

E.S.R. spectra of X-irradiated methylene diphosphonic acid

X-irradiation of single crystals of methylene diphosphonic acid gives rise to E.S.R. spectra which have been assigned to (OH)₂(O)P-?H₂ and

The former species is the more abundant of the two and the methylene group undergoes rapid re-orientation about a two-fold axis at room temperature but is stationary at 77 K. The ¹H and ³¹P coupling constants in this radical are very similar to those in Ph₃P⁺CH₂, and support the previous conclusions [1] that there is little delocalization of the unpaired electron to the phosphorus atom.     

E.S.R. spectra of SiF3 radicals produced in a single crystal of SiF4

E.S.R. spectra of a γ-irradiated single crystal of SiF₄ were investigated. The spectra observed were attributed to SiF₃ radicals having ²⁸Si (I=0) and ²⁹Si (I=1/2) atoms. From the angular dependence of the spectral lines on rotation of the single crystal, hyperfine tensors were determined for three fluorine atoms and the ²⁹Si atom of the SiF₃ radical. The three fluorine atoms in the radical are equivalent, whereas the directions of their hyperfine tensors are different from one another owing to the pyramidal structure of the radical. In addition to the hyperfine analysis, the analysis of the superhyperfine structure due to neighbouring fluorine atoms gave information on the orientation of the radicals in the crystal and the mechanism of radical formation. The structure of the radical is discussed in comparison with that of the CF₃ radical.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.     

Dynamic frequency shift in the E.S.R. spectra of transition metal ions

The factors which determine the electron spin resonance lineshapes and shifts of transition metal complexes in solution are discussed. It is shown that for ions with S > ½ the dynamic frequency shift may have pronounced effects on the E.S.R. lineshapes, and experimental evidence for this effect in complexes of Cr³⁺, Fe³⁺ and Gd³⁺ is presented. A quantitative interpretation of these spectra in terms of a relaxation mechanism due to fluctuation of the quadratic zero field splitting interaction is given.     

Neutron elastic and inelastic scattering from 28Si, 32S and 34S

Differential cross sections for the elastic and inelastic scattering of neutrons from the sd-shell nuclei ²⁸Si, ³²S and ³⁴S have been measured in the 20–26 MeV region. The data are analyzed in terms of the rotation-vibration (²⁸Si) and anharmonic vibration (^{32, 34}S) collective models. Isoscalar E2, E3 and E4 transition matrix elements are obtained from the normalized multipole moments of the real potential and the results are compared with those obtained from electromagnetic probes and from nuclear structure theoretical calculations.     

Properties of vanadium in InP

Experiments are performed on InP/V single crystals extracted from a polycristalline ingot grown in a two zones gradient freeze furnace; in photoluminescence (PL) we observe a band with two zero phonon lines at 5692.5 cm^-1 and 5705.5 cm^-1. Photoluminescence excitation (P.L.E.) spectra have also been observed. This type of luminescence spectra has already been observed in V doped GaAs and GaP and attributed to an internal transition of V²⁺ (3 d³). D.L.T.S. and O.D.L.T.S. experiments do not reveal any deep level in the forbidden band gap. These two results seem to indicate a puzzling behaviour of V in InP as in GaAs which is discussed in the framework of a model proposed for GaAs/V : the V²⁺ ground state has a large relaxation energy and so, the excited states giving rise to the P.L. and P.L.E. spectra are not resonant with the conduction band.     

E.S.R. Study of copper and silver N,N-dialkyldiselenocarbamates

Single crystal E.S.R. studies of Cu(II) and Ag(II) dialkyldiselenocarbamates, diluted in the corresponding Ni(II) complexes, are reported. A method has been developed which removes the necessity to measure the spectra on the same single crystal and in three mutually orthogonal planes. Equations have been derived for the resonance fields and the transition probabilities, taking into account the full spin hamiltonian and without assuming coinciding tensor axes. Applying these equations the g tensor and the metal hyperfine and quadrupole coupling tensors are obtained in high precision. In contrast to the situation in the corresponding dithiocarbamates, it was found for all diselenocarbamates studied that the axes of the g and metal hyperfine tensor do not coincide and that the relative orientation depends on the central metal ion and on the molecular symmetry. The highest g value was always found in the molecular plane, whereas in the dithiocarbamates the highest value is found perpendicular to the molecular plane. The spectra reveal the presence of two sets of two equivalent Se atoms, so that the molecule has inversion symmetry. Especially from the measured ⁷⁷Se hyperfine splittings it could be concluded that the built in guest molecule accepts the structure of the host crystal. Also measurements are reported on powders, glasses and liquid solutions. Evidence has been obtained that in the latter two media the g and metal hyperfine principal axes coincide.     

Photoproton cross section of 34S

Measurements of the ³⁴S(γ, p) and ³⁴S(γ, np) cross sections are reported. The ³⁴S(γ, p) cross section shows two regions of strength, at 17 and 22 MeV, consistent with that seen in the ³⁴S(γ, n) cross section.A particle-hole calculation is made for the dipole absorption cross section in ³⁴S. The photoproton and photoneutron cross sections calculated on the assumption of statistical decay of GDR states under the constraints of isospin selection rules, agree well with those seen experimentally.     

The structure of 32S II. Shell model interpretation

The properties of positive-parity states in ³²S are compared to predictions of shell model calculations within the complete s-d basis space using the universal s-d shell Hamiltonian. The experimental T = O spectrum is reproduced to excitation energies between 10 and 11.7 MeV, depending on the level spins. The T = 1 spectrum is known and reproduced for the first five 5 MeV in excitation in general and for the first 8 MeV in the case of I^π = 1⁺ states. Altogether the excitation energies of 80 positive-parity states are reproduced with a rms deviation of 200 keV. A calculation of radiative widths and branching ratios for γ-decay which uses effective charges and free-nucleon g-factors yields good general agreement with experiment. The need for effective g-factors is felt only in the rare cases of transitions which are governed by the isovector d_3/2 → d_5/2 M1 matrix element. The spectrum of negative parity, T = 1 states is understood in terms of the weak-coupling model while that of the T = 0 states is comprised of octupole-quadrupole phonon multiplets. Positive-parity states from outside the s-d configuration are first observed between 9.5 and 10.5 MeV excitation energy.     

An investigation of excited states in32S by the31P(p, γ)32S reaction

The³¹P(p, γ)³²S reaction has been studied in the proton energy region 300–1420 keV using Ge(Li)-techniques. Gamma decay schemes of 16 resonances are proposed. The branching ratios of the resonance states and 23 bound states are presented. The spin of theE _x=7116 keV level was found to beJ ^π=2⁺. In addition, the present results are compared with earlier ones.     

E0 transition and coupling between quadrupole and pairing-vibrational modes

Using a theory of mode-mode coupling between the two-phonon 0⁺ mode and the pairing-vibrational mode, we have extensively investigated the first excited 0⁺(0₂²) states in spherical and transitional nuclei. The results tell us that the 0₂⁺ states in a wide range of nuclei are strongly mixed states of both the modes. By making use of these results, the matrix elements for the E0 transitions from the 0₂⁺ states to the ground states are calculated for the Zn, Ge, Se, Kr, Sr, Zr, Mo, Ru, Pd, Cd and Sn isotopes. For some of the Cd and Sn isotopes, the matrix elements between the 0₂⁺ and 0₂⁺ states are also obtained. These numerical calculations make a rather good fit to the E0 experiments.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

Cross sections for photodisintegration of 32S to excited residual states

Cross sections and integrated cross sections for photodisintegration of ³²S to specific residual states in ³¹P and ³¹S have been measured. Comparison with spectroscopic factors for nucleon pickup reactions on ³²S leading to the same residual states are made. It is concluded that the creation and decay of the dipole state in ³²S is predominantly a single-nucleon interaction.     

Asymmetric line-width effects in the presence of resolved second order splittings: the E.S.R. spectra of 1,1-difluoroalkyl radicals in fluid solutions

The solution E.S.R. spectra of radicals of the type R?F₂ exhibit marked line broadening attributable to rotational modulation of the ¹⁹F anisotropic hyperfine interactions. This dipolar broadening is restricted to lines associated with the triplet state of the two equivalent ¹⁹F nuclei and for slowly rotating radicals only the singlet state line is readily detectable.     

Bulk viscous L.R.S. Bianchi type V tilted stiff fluid cosmological model in general relativity

Locally rotationally symmetric (L.R.S.) Bianchi type V bulk viscous tilted stiff fluid cosmological model is investigated. To get the deterministic model of the universe, we have also assumed a condition A=Bⁿ between metric potentials A, B where n is the constant. The behaviour of the model in presence and absence of bulk viscosity and singularities in the model are also discussed. In general, the models represent accelerating, shearing, tilted and non-rotating universe. The models have point type singularity in presence and absence of bulk viscosity both.     

An E.S.R. study of some alkyl substituted benzene anion radicals : an experimental evaluation of the extent of vibronic interaction

E.S.R. studies of the proton hyperfine splitting in the anion radicals of benzene, toluene, ethylbenzene, iso-propylbenzene, t-butylbenzene, and p-xylene show that it is strongly dependent upon temperature. In the case of the monoalkylbenzenides there are two contributions to this observed temperature dependence. First, there is a rapid thermal averaging over two near-degenerate states which have different spin-density distributions. The energy separations between these two near-degenerate states have been measured for the above series of monoalkylbenzenides and are reported here. It is also possible to measure experimentally the spin-density distributions for the two states between which the averaging takes place. With this information one can obtain an experimental estimate of the extent of vibronic interaction which occurs in these systems. Such estimates are presented here and compared with those obtained theoretically. The second source of the strong temperature dependence of the proton hfs lies in the temperature dependence of the sigma-pi interaction parameter, Q _H. The sigma-pi interaction parameter has been studied as a function of temperature for all members of the above series and the results reported. Finally, restricted rotation of the iso-propyl group in the anion radical of iso-propylbenzenide was observed and the barrier to rotation has been measured.     

Three photon resonant ionization in atomic potassium via S,P, D and F series Rydberg states

Single colour three photon resonant ionization (2 + 1) is observed in atomic potassium vapour in a heat pipe oven using an excimer laser pumped dye laser. Using wavelengths between 570 nm and 603 nm various²S and²D Rydberg states are populated by two photon excitation. Third photon of the same wavelength ionizes the atoms. Rydberg states up ton ⋍ 50 are observed. Electric field as low as 1 V/cm causes extensive Stark mixing of the states. This results in progressively higher three photon ionization signals via the perturbed²P and²F Rydberg states. The three photon ionization process is studied using both linearly and circularly polarized incident light. The experiment shows qualitatively that the²P Rydberg states are perturbed primarily by the²D states in the prescence of an external electric field and to a much smaller extent by²S states. This is also explained theoretically by calculating the Stark mixing coefficients under the Bates and Daamgard (1949) approximation. Implication for a similar effect in other alkali elements is discussed.