Showing papers on "Spin states published in 1970"
TL;DR: In this paper, a detailed measurement of the magnetic field dependence of the rate of mutual annihilation of triplet excitons in anthracene crystals at room temperature is presented, and the amplitude of the field dependence is highly anisotropic.
Abstract: Detailed measurements of the magnetic field dependence of the rate of mutual annihilation of triplet excitons in anthracene crystals at room temperature are presented. The field dependence consists of an increase at low fields, with a maximum at ca. 350 Oe, followed by a decrease at higher fields to less than the zero-field annihilation rate. For most field directions, a second maximum occurs at ca. 600 Oe. The amplitude of the field dependence is highly anisotropic. For fields g2000 Oe, resonances in the annihilation rate are found at +76\ifmmode^\circ\else\textdegree\fi{} and -17\ifmmode^\circ\else\textdegree\fi{} with respect to the $a$ axis for fields in the $\mathrm{ac}$ plane and at \ifmmode\pm\else\textpm\fi{}23.5\ifmmode^\circ\else\textdegree\fi{} with respect to the $b$ axis in the $\mathrm{ab}$ plane. For fields 500 Oe, a second set of resonances occurs at directions bisecting the high-field resonances and at intermediate fields the two sets coexist. These results are discussed in terms of a density-matrix description of the spin states of the interacting triplet pair and of the annihilation process. The field dependence is accounted for on the basis of the field dependence of the pair spin states together with the postulate that annihilation is spin-allowed. The observed resonances result from level crossings among the pair spin states. All of the structure in the field dependence and anisotropy data is satisfactorily reproduced by calculations based on the model, although complete quantitative agreement is not achieved.
312 citations
TL;DR: It is concluded that P-450(cam) as isolated is equal to or more than 95% in a low spin form probably having sulfur as one of the axial ligands.
Abstract: The electron paramagnetic resonance signals of the soluble P-450 cytochrome from Pseudomonas putida were observed at temperatures from 42 to 80°K As isolated, P-450 has a signal typical of a low spin ferric-heme compound with sulfur as one of the axial ligands (g = 245, 226, 1915) We also detected a minor signal typical of high spin ferric heme (g = 8, 4, 18) equivalent to less than 7% of the heme at temperatures below 20°K On titration with the substrate, (+)-camphor, the low spin signal decreased and the high spin signal increased, maximally representing about 60% of the heme For reasons not thus far understood, 40% of the heme is not converted to high spin by either (+) or (-)-camphor The high spin signal has a rhombic character which is stronger than any previously observed with a heme compound (E = 033 cm-1; D = 38 cm-1; E/D = 0087)
We conclude that P-450cam as isolated is equal to or more than 95% in a low spin form probably having sulfur as one of the axial ligands The binding of substrate displaces this ligand sufficiently to allow for conversion from a low to a high spin form
251 citations
TL;DR: In this article, the average magnetic susceptibility of manganese phthalocyanine in the range 1.7-300°K was reported, which confirmed that the Mn(II) atom is in an S 1/3/2 spin state, and that weak ferromagnetic interactions are present in the crystal.
Abstract: Measurements are reported of magnetization and the average magnetic susceptibility of manganese (II) phthalocyanine in the range 1.7–300°K, which confirm that the Mn(II) atom is in an S = 3 / 2 spin state, and that weak ferromagnetic interactions are present in the crystal, presumably between adjacent molecules. Single crystals of MnPc are moderately anisotropic; the principal magnetic moment μ‖ = 4.0 μB remains constant between 80–300°K while μ⊥ increases from 4.4 μB (300°K) to 5.0 μB (90°K). This magnetic anisotropy is consistent with a 4A2g ground state into which the excited term 4Eg is mixed by spin–orbit coupling. Possible pathways for superexchange are considered.
112 citations
TL;DR: The combination of metalloporphyrins to apohemoproteins appeared to be an excellent method of achieving an ideal magnetic dilution of paramagnetic centers for EPR studies.
69 citations
TL;DR: In this paper, the theory of antisymmetrized products of separated geminals for many-electron systems is developed for arbitrary spin states, and methods are developed for their optimal determination.
Abstract: The theory of antisymmetrized products of separated geminals for many‐electron systems is developed for arbitrary spin states. The geminals are expanded in terms of their natural spin orbitals, and methods are developed for their optimal determination. New variational equations are derived and cast in the form of one pseudoeigenvalue equation for all natural spin orbitals. An alternative scheme is given for finding optimal symmetry‐adapted natural orbitals in terms of an orthonormalized basis set by direct energy minimization. A strategy for optimization is discussed which was found useful in calculations of the ground states of the molecules LiH, BH, NH, and their separated atoms.
68 citations
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TL;DR: Basic Principles of Ligand Field TheoryBy H. L. Schlafer and G. Gliemann.
Abstract: Basic Principles of Ligand Field Theory By H. L. Schlafer and G. Gliemann. Translated by D. F. Ilten. Pp. xv + 535. (Wiley (Interscience): London and New York, 1969.) 160s.
67 citations
TL;DR: In this article, a simple particle-hole model was used to obtain inelastic electron scattering form factors and investigate the usefulness of Wigner supermultiplet theory as a predictive tool in studying weak and electromagnetic processes in light closed-shell nuclei.
61 citations
TL;DR: In this article, the authors used the reaction 154 Sm(α, 3n) 155 Gd to populate states in the positive-parity band and observed Cascade and crossover transitions within a strongly perturbed rotational band.
57 citations
TL;DR: EPR studies of the lowest triplet state of anthracene in a phenazine host crystal reveal a non-Boltzmann distribution over the triplet spin levels of ≈ 1.5°K.
44 citations
TL;DR: The electron spin resonance spectra of low spin ferric heme proteins are calculated and compared with experimental spectra recently obtained, and the possibility that the g value variation in these different types of proteins is due to systematic environmental changes is explored.
43 citations
TL;DR: In this paper, the b-axis magnetizations of a single crystal of manganese phosphide are studied in detail in the range of magnetic field up to 80 kOe at various temperatures.
Abstract: Magnetizations in the three main planes of a single crystal of manganese phosphide are measured at 4.2°K. Especially the b -axis magnetizations are studied in detail in the range of magnetic field up to 80 kOe at various temperatures. The screw-spin state of ferromagnetic spin state transforms to the state and than to the complete paralell arrangement by the external magnetic field applied along the b axis. From the results obtained, the spin structure diagram is made as a function of temperature and of magnetic field applied along the b axis.
TL;DR: In this article, a mechanism based on the adiabatic development of radical pair spin states during chemical reactions is proposed to explain ESR emission/absorption spectra of transient radicals and NMR-emission/absorbation spectras of their reaction products.
TL;DR: The high-pressure chemistry of iron in the solid state is rich in new phenomena as discussed by the authors, and the effect of pressure on the interelectronic repulsion parameters and the ligand-to-metal charge transfer peaks is investigated.
TL;DR: The metal-ligand stretching frequencies of first transition series metal(III) complex oxalates, K3[M(C2O4]3·3H2O, have been determined and their crystal field stabilization energies (CFSE's) calculated.
TL;DR: In this article, a modified form of the combined interpolation (tight-binding plus pseudopotential) method was applied to the calculation of energy bands in ferromagnetic nickel, and a procedure was developed to enable calculation of the reciprocal spin-wave effective mass in a multiband system in the $t$-matrix approximation.
Abstract: We have applied a modified form of the combined interpolation (tight-binding plus pseudopotential) method to the calculation of energy bands in ferromagnetic nickel. A procedure has been developed to enable calculation of the reciprocal spin-wave effective mass in a multiband system in the $t$-matrix approximation. This has been used in conjunction with the calculated band structure. Matrix elements of the electron interaction are treated as parameters. A by-product of the calculation is an estimate, also in the $t$-matrix approximation, of the energy difference between majority and minority spin states in the highest $d$ band. Moderately good results for the spin-wave effective mass are obtained for reasonable values of the electron interaction parameters; however, a discrepancy is found in regard to the spin splitting, which appears to be too large.
TL;DR: In this paper, the authors investigated the properties of a conduction electron in a ferromagnetic crystal (magnetic polaron) and showed that, for certain total spin states, a slight narrowing of the electron bandwidth can occur, depending on the magnitude of the atomic spin.
Abstract: The properties of a conduction electron in a ferromagnetic crystal (magnetic polaron) have been investigated. The magnetic spins are treated within the idealized boson representation. At absolute zero a large number of terms in the perturbation expansion are zero and the remainder can be summed exactly. For strong coupling it is demonstrated that, for certain total spin states, slight narrowing of the conduction electron bandwidth can occur. This narrowing depends on the magnitude of the atomic spin in the form of a factor 2s/2s+1.
TL;DR: In this paper, the level structure of high-spin states in Xe isotopes is discussed and γ-ray intensities, angular distributions and excitation functions have been made.
TL;DR: In this article, it was shown that at low temperatures the electron resonance spectrum of manganous ions dissolved in methanol exhibits an unexpected and unusual dependence on the nuclear quantum number.
TL;DR: In this paper, the hyperfine coupling constants for NH+3 were calculated to be aN= 10.57, aH= −22.65 G using the ab initio UHF method after spin annihilation of the quartet spin state and optimization of the NH bond length and hydrogen atom orbital exponent.
Abstract: The hyperfine coupling constants for NH+3 are calculated to be aN= 10.57, aH=–22.65 G using the ab initio UHF method after spin annihilation of the quartet spin state and optimization of the NH bond length and hydrogen atom orbital exponent. It is calculated that the effect of the out-of-plane zero-point energy vibration modifies the hyperfine coupling constants to aN= 16.92, aH=–20.02 G.
TL;DR: In this paper, the low-lying states in 55 Fe were studied using the 55 Mn(p, nγ) 55 Fe reaction, and the measurement of γ-ray angular distributions together with predictions based on the compound nuclear statistical model has permitted unique spin assignments to be made to the following excited states.
TL;DR: Molecular orbital calculations based on representative porphyrin geometries predict a decrease in the phosphorescence energy as the hole size increases, a prediction in agreement with data in the literature on metal mesoporphyrins.
Abstract: Correlations were found between the hole size of 10 metalloporphyrins, determined by x‐ray crystallography, and the ionic radius of the central metal atom, derived from a new compilation of ionic radii as a function of coordination number, spin state, and valence. These correlations were used to define representative porphyrin geometries for each of three different hole sizes. We recommend the use of these geometries for future molecular‐orbital calculations. Molecular orbital calculations based on these porphyrin geometries predict a decrease in the phosphorescence energy as the hole size increases, a prediction in agreement with data in the literature on metal mesoporphyrins. Experimental excitation energy of the singlet Soret (but not the visible) band also decreases with increasing hole size, a result not given by calculations using either four‐orbital or extensive configuration‐interaction models. Electronegativity has a statistically significant effect on the lowest excited singlet and, to a lesser extent, the lowest triplet energy. Changes in hole size produce little change in calculated bond order, indicating that structural changes induced by increased hole size are due to strain induced in sigma bonds. There is no correlation between either singlet or triplet energy and the charge density of the central metal atom as determined by previous molecular‐orbital calculations. Thus, the primary effect of changing metals on the lowest triplet state of metal porphyrins is due to effects on the pi electrons of the geometric distortion of the porphyrin ring imposed by the steric requirements of the central metal atom. The effect of the central metal on the singlet energies remains to be fully explained.
TL;DR: In this article, a physical picture of the origin of the zero field splittings and levels of the three zero field spin states of aromatic molecules is given at very low temperatures (<2°K), where the spin-lattice relaxation processes between these levels can be frozen.
Abstract: A physical picture of the origin of the zero field splittings and levels of the three zero field spin states of aromatic molecules is given At very low temperatures (<2°K), the spin—lattice relaxation processes between these levels can be frozen Under these conditions, the emission properties of the lowest triplet state are the sum, rather than the population-weighted average, of those of the different emitting zero field levels Since the rates of pumping and deactivating the different zero field levels of the lowest triplet states are most likely to be unequal, the steady-state population of these three levels becomes unequal, ie a state of spin alignment in one molecular direction can be produced A number of phosphorescence-microwave multiple resonance experiments can thus be carried out from which the following information can be determined: (1) the zero field origin of each vibronic band in the phosphorescence spectrum; (2) the relative rates of the non-radiative intersystem crossing process to the individual zero field levels of the lowest triplet state (and thus the mechanism of the intersystem crossing process); (3) the magnetic energies required to change the electron spin as well as the nuclear spin directions in the molecular framework in the absence of a laboratory magnetic field (but in the field of the two unpaired electrons in the lowest triplet state); and (4) spin-direction selection rules in the intermolecular triplet—triplet energy transfer process The possibility of controlling the rate of a photochemical reaction involving the triplet state by saturating the zero field transitions with microwave radiation is briefly discussed
TL;DR: In this paper, the shape of the 40 MHz proton magnetic resonance absorption line of powdered (NH4)2Ce(NO3)6 at liquid helium temperature is explained by proton spin isomerism as suggested by Tomita for solid methane.
TL;DR: In this paper, the authors used the splitting of the resonance dip in the absorption cross section to measure the local electric field gradients at a single atomic site in a crystal, which can be applied to sites occupied by nucleii whose ground states have no quadrupole moments and which cannot be used to detect the EFG unless they are excited into a higher spin state.
Abstract: We have seen in Part 1 that a resonance observed at a single atomic site in a crystal can give information about the local electric field which depends on crystal structure. To obtain a unique structural picture in this way, one must observe resonances at as many sites as possible, and therefore we are interested in a technique which can be applied to sites occupied by nucleii whose ground states have no quadrupole moments and which cannot be used to measure the EFG unless they are excited into a higher spin state. For example Fe57 has S = 1/2 in the ground state, but it can absorb a low-energy gamma ray to form an S = 3/2 excited state which will be split by quadrupole interaction with the EFG. One can thus examine the local field gradients by measuring the splitting of the resonance dip in the absorption cross section.
TL;DR: The theoretical interpretations of electron spin resonance signals from defect centres with g factors close to those of the free spin values are discussed in this article, and it is shown that accounting fully for the observed g shifts has important implications for the theory.
Abstract: The theoretical interpretations of electron spin resonance signals from defect centres with g factors close to those of the free spin values are discussed. It is shown that accounting fully for the observed g shifts has important implications for the theory. These involve a bridging of the gap between the local model approximations of crystal field theory and the more extensive band theory ideas, in addition to questions concerning the expansion or contraction of free-ion non-electron wave functions on formation of a solid. Another aspect concerns evidence for configurational mixing of different free ion-electron configurations by large crystal fields of low symmetry.