A study of the effect of non-collinear Zeeman,hyperfine and fine structure tensors on E.S.R. spectra

Second order perturbation solutions are given to the general experimental hamiltonian :

where the axes of the g, D and A tensors may be non-collinear. The effects of the non-collinearities are discussed in terms of the modifications of the E.S.R. parameters for both single crystal and polycrystalline samples. The principles are illustrated for the E.S.R. of the formyl radical from published single crystal and powder data.     

Rapid computer simulation of E.S.R. spectra

A fast computer algorithm is presented which permits simulation of the effects of rotational diffusion, electron and nuclear relaxation, microwave power, and modulation frequency upon saturation transfer (passage) E.S.R. spectra. Comparison of theoretical and experimental spectra for nitroxide spin-labelled biomolecules suggests that while the dependence of electron spin-lattice relaxation time upon rotational correlation time is weak, the variation of the ratio of the electron to nuclear spin-lattice relaxation times is significant and consideration of strong nuclear relaxation is necessary for the simulation of spectra characterized by correlation times near the reciprocal of the nitrogen nuclear resonance frequency.     

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. spectrum of 3,5-lutidine anion and comments on nitrogen hyperfine couplings

The E.S.R. spectrum of the 3,5-lutidine anion has been observed. The methyl groups prevent the dimerization which occurs for pyridine. From the observed splitting constants and those of the pyrazine negative ion an estimate is made of the relative contribution to the nitrogen hyperfine splitting of the π-orbital spin densities on the nitrogen atom and on the adjacent carbon atoms.     

The E.S.R. and electronic absorption spectra of Chichibabin's biradical

The absorption spectra of a number of saturated hydrocarbons in the vacuum ultra-violet region have been examined and compared with their photoelectron and electron-loss spectra. Important conclusions about the quantum defect associated with the excited electrons and the nature of the excited states have been drawn from the relative positions of these spectra. The Rydberg bands of ethane, which were initially thought to originate in the C-C bond, have been shown to be associated with an electron largely localized in the CH₃ group.     

E.S.R. spectra of diboranyl radicals in the solid states

E.S.R. Spectra of the radicals produced from the γ-irradiated diborane (6) in polycrystal or single crystal have been investigated. From the analysis of the results of the single crystal, the radical was identified as neutral diboranyl, ·B₂H₅, produced by extracting one of the two bridging hydrogen atoms of diborane. The major portion of the spin density on the radical is equally shared by the two boron atoms, a considerable portion exists on the bridging hydrogen atom, and a small portion with negative sign on the four terminal hydrogens. The orbitals of the unpaired electron on the two borons are in the same plane at an angle of 73°. These results are in good agreement with those from INDO calculation for the radicals. The structure of the radical is discussed in comparison with some other radicals having a similar structure.     

The McConnell equation for E.S.R. spectra of symmetrical diazanaphthalenes

Electron spin resonance spectra of the six symmetrical diazanaphthalene anions in N,N-dimethylformamide have been measured. The anions were generated within the microwave cavity by electro-reduction of the parent compound. The McConnell equation a _H = Q _CC ^H ρ C has been tested for the diazanaphthalenes with ρ C values calculated by the Hückel method and by the Pariser-Parr-Pople S.C.F. method with variable resonance integrals.     

On the Mössbauer hyperfine spectra of paramagnetic clusters

The hyperfine interaction of a system containing two weakly coupled paramagnetic ions is investigated. It is shown that even a very weak interaction cannot be broken by a large magnetic field, if the Zeeman interaction of the two paramagnetic centers is identical. Small differences in theg-values, however, yield immediately a quite different hyperfine pattern which corresponds to two isolated paramagnetic centers in the case of a large external magnetic field. Mössbauer experiments on reduced bacterial ferredoxin where one molecule contains two iron clusters withS=1/2 each are used to analyze the interaction of two paramagnetic centers.     

Evidence for slow exchange in E.S.R. spectra of nitroxide biradicals

Force constants have been calculated for H₂NF and HNF₂ from ab initio Hartree-Fock wavefunctions by the force method, using 7s3p/1 gaussian basis sets. The force field of HNF₂, obtained from a combination of the theoretical results with the experimental frequencies, can be considered as the most reliable one at present. Previous force fields are discussed critically. From a full optimization the predicted geometry of H₂NF is: NF = 1·399 Å, NH = 1·018 Å, HNF = 102·9° and HNH = 105·9°.     

原子光谱中同位素位移和超精细结构分裂

利用共线快离子束-激光光谱学方法测量了钕离子所有7个稳定同位素(A=142～146,148,150)之间的同位素位移和两个奇同位素(A=143,145)的超精细结构分裂．     

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.     

Interpretation of S-state ion E.P.R. spectra

Although a considerable body of data exists on the parametrization of the ground-state splittings of S-state ions in crystals, relatively little progress has been made in obtaining a quantitative understanding of the mechanisms which determine these parameters. In the course of summarizing our present understanding, we emphasize the need for making planned experiments explicitly aimed at testing theoretical models, such as those proposed in this article. The variable frequency E.P.R. technique is described in some detail, as it has proved to be particularly useful in this respect.     

Effects of collisional interference of lines in the spectra of symmetric top molecules: III. Broadening of rotational transitions with a hyperfine structure

The peculiarities of the broadening of rotational transitions of molecules in the case where the spectrum exhibits a hyperfine structure caused by the nuclear quadrupole interaction are considered. The relaxation parameters of the components of a number of hyperfine multiplets of CH₃I molecules are calculated taking into account self-broadening, and calculations are compared with experiment.     

运用光电流光谱测定钬原子能级的超精细结构

用自制钬空心阴极灯,运用光电流光谱技术在569nm～600nm谱区内首次测定了元素钬的9条谱线,确定其相应跃迁能级,及超精细结构常数.     

E.S.R. spectra of PF4 radicals produced in a single crystal of PF3

E.S.R. spectra of PF₄ radicals were investigated with single crystals of PF₃ made at a low temperature and irradiated with γ-rays. The angular dependence of the spectral lines was satisfactorily analysed in terms of the second-order equations for large couplings of one ³¹P nucleus and two magnetically equivalent ¹⁹F nuclei and of the first-order equation for two ¹⁹F nuclei with small couplings. We conclude that the two magnetically equivalent fluorine nuclei occupy the axial positions of the trigonal bipyramidal structure of the PF₄ radical and the other two fluorine nuclei are in the equatorial positions. Furthermore, the unpaired electron of the PF₄ radical was shown to occupy an orbital consisting mainly of the 2p orbital of each of the two axial fluorine atoms along the F-P-F axis and the 3s and 3p orbitals, directed towards the vacant equatorial position of the central phosphorus atom. The orbital of the unpaired electron can be reasonably represented as a Rundle three-centre non-bonding orbital. The results obtained for the PF₄ radicals not only strongly support the results given for POCl₃ ^- radicals, but also allow us to discuss the electronic structure of phosphoranyl radicals in more detail.     

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.     

An E.S.R. study of the structure of phosphorus centred radicals in solution

Clementi and Veillard's analysis of the MC SCF theory of closed-shell systems is developed on a different basis. An equivalent Hartree-Fock operator is defined and its physical significance is discussed. A generalized Brillouin theorem is derived, different from that given by Levy and Berthier.     

E.S.R. spectroscopy of non-cyclic enones

The π-bond model is applied to the calculation of the proton chemical shifts of a range of benzenoid hydrocarbons. The simple calculations give results which compare well with experiment and with calculations based on the ring current model. Least squares fitting of the predicted chemical shifts to the observed values can give an indication of the occurrence of local aromatic groups in larger molecules. This procedure also yields an empirically adjusted estimate of the anisotropy in the molar magnetic susceptibility from the experimental proton chemical shifts. A simple criterion for aromaticity is also given. The overall results suggest that there is no need to associate a special ring current attribute to π conjugation in aromatic molecules.     

Reinvestigation of the quadrupole hyperfine structure in rotational spectra of chloroiodomethane

The b-type Q-branch transitions of chloroiodomethane were remeasured and the quadrupole hyperfine structures were reinvestigated by a new method to improve the discrepancies in the hyperfine spectra observed and calculated in a previous work. The χ values of the off-diagonal element of ³⁵Cl and ³⁷Cl were determined. The nuclear quadrupole coupling constants were revised to be χ_aa = −1421.9 ± 1.9, χ_bb = 392.6 ± 1.0, χ_cc = 1029.3 ± 2.1, and {χ_ab} = 1174.9 ± 1.7 MHz of iodine; χ_aa = −31.1 ± 1.1, χ_bb = −9.0 ± 0.6, χ_cc = 40.1 ± 1.2, and {χ_ab} = 53.6 ± 4.2 MHz of ³⁵Cl for ³⁵Cl species; χ_aa = −1418.4 ± 2.5, χ_bb = 386.5 ± 2.7, χ_cc = 1031.9 ± 3.6, and {χ_ab} = 1181.8 ± 1.7 MHz of iodine; and χ_aa = −21.1 ± 1.7, χ_bb = −8.5 ± 0.9, χ_cc = 29.6 ± 1.9, and {χ_ab} = 34.6 ± 1.4 MHz of ³⁷Cl for ³⁷Cl species, respectively.