HFS Lines Research Articles

Laser-induced shifts and splittings of hyperfine structure lines in electron spin resonance spectra of 35Cl atoms

Laser-induced shifts and splittings of the hyperfine structure (hfs) lines in the electron spin resonance (ESR) spectra of 35Cl atoms have been studied using both dressed-atom theory and semiclassical dispersion theory. In resonant cases, the calculated results by the dressed-atom theory of the ac Stark effect indicate that laser-induced hfs ESR shifts of 35Cl atoms in the ground state 3p5 2P0 3/2 can be more than 1 MHz W−1 cm2, and a single ESR hfs line is split into four lines under the action of a laser beam with intensity 10 W cm−2. In non-resonant cases, the two theories give similar results for the shifts. The laser-induced broadening of the ESR hfs lines is also calculated and is less than the shifts. The laser-induced shifts in ESR can be observable within the resolution of ESR experiments.

EPR of radiation defects in LiBaF 3 crystals

EPR spectra of LiBaF 3 crystals have been investigated after X-irradiation at RT. A spectrum consisting of approximately 35 nearly equidistant EPR lines has a strong angular dependence on the line intensities. The spectrum is caused by a hyperfine interaction (hfs) of a spin S =1/2 with neighbouring groups of nuclei. The observed large number of hfs lines required Li nuclei being in the first shell and fluorine nuclei in the more distant second shell. We analysed the spectrum in the F -centre model, taking reduced hfs values of the F -centre in LiF and found qualitative explanation of the number of hfs lines. The angular dependence of the line intensities could be explained by an anisotropy of the g -tensor with its main axis along the [1 v 0 v 0] axis of the crystal.

Some peculiarities of the EPR spectra of radiation-induced defects in LiF and NaF crystals

To refine the structure of radiation-induced defects, a comparison is made of the EPR spectra of LiF and NaF crystals with various constituent impurities γ-irradiated with different doses, as well as the experimentally measured and calculated intensity distributions of HFS lines in the EPR spectra of these crystals. It is shown that the F-centers, whose model represents an ionized quasimolecule consisting of two metal atoms on each side of a halide vacancy, are responsible for the broad band observed independently of the impurity composition of the crystals and irradiation dose, while the HFS is caused by defects based on interstitial halide atoms.

Laser Spectroscopy of the H 2 ( n = 3 Triplet Gerade) Complex: Fine and Hyperfine Structure of the Levels in ortho-H 2

The measurements of the preceding paper of this series were extended to the v = 0 and 1 levels of ortho-H 2. In this ease the additional hyperfine structure, which is comparable in magnitude to the fine structure in the n = 3 states, complicates the line profile patterns greatly. Because of strong mixing of fs and hfs interactions, even the identification of the line components was not straightforward. It was accomplished by means of an approximative line profile simulation, based on estimated coupling constants. The necessary matrix elements are given here for the first time. In a second iteration step, the final set of 20 hfs coupling constants was then obtained through a comprehensive fit to the large number (84) of measured hfs splittings. The Fermi contact constants were determined to within 2-3%, or 10 MHz. Many of the smaller constants were, however, found to be highly statistically correlated, similar to the results of the preceding paper. As a set they have, however, collective significance, as is demonstrated by the very successful simulation of the overall hfs line profile.

Magnetic field effects in radical pair recombination. II. Spin exchange relaxation and CIDN(E)P in bulk recombination

The method of analytical solution of the stochastic Liouville equation developed in the previous paper is applied to derive the Bloch equations describing spin exchange relaxation (SER) and magnetic field effects such as CIDNP and CIDEP in bulk recombination of radicals. Simple analytical expressions for transversal and longitudinal SER rates are obtained which are applicable in the limit |Q|/ Dα 2 ⪡ 1, where Q is the characteristic intraradical magnetic interaction (hfi etc.), D is the relative diffusion coefficient and α −1 is the characteristic size of the exchange interaction potential. These expressions show that in the low viscosity limit | Q| d 2/ D ⪡ 1, where d is the distance of closest approach, the transversal SER rate is equal to the longitudinal one. However in the opposite limit of high viscosity transversal SER rate becomes two times larger than the longitudinal one. These formulae also predict the appearance of significant phase shifts of hfs lines (comparable with the SER line widths) due to SER in the high viscosity limit. The rigorous relation between polarization enhancement in bulk radical recombination and the value of chemically induced dynamic polarization arising in geminate recombination of radical pairs is found. Some experimental investigations of SER and CIDEP in bulk recombination are analyzed by the theory developed. It is shown that such an analysis gives valuable information on the interaction and relative motion of radicals in liquids.

SELECTION FOR YIELD AT TWO FERTILIZER LEVELS IN SMALL-SEEDED COMMON BEAN

Selection for seed yield (visual in the F2, visual and plot yield from the F3 to F5, and yield tests in F6) was carried out in two crosses of common bean (Phaseolus vulgaris L.) in high and low soil fertility environments at CIAT-Quilichao, Colombia. Parents were small-seeded and tolerant to low soil phosphorus, possessed indeterminate bush growth habit, and belonged to lowland tropical gene pools of Middle America. The mean yield of selected lines from low (LFS) and high (HFS) soil fertility environments was significantly higher than the mean of the parents in both crosses when tested in high fertility (HF) but not in low fertility (LF). The highest yielding LFS and HFS lines from A 286 × (G 5059 × A 80) and the LFS line from A 286 × ICA Pijao outyielded the best check cultivar, Carioca, in HF. No line yielded significantly more than A 286, the best parent used in both crosses. The mean effect of fertilizer levels on selection for seed yield was nonsignificant. Lines selected under two environments showed similar but average response and high stability of performance under variable environments. Low soil fertility accelerated maturity and reduced 100-seed weight and seed yield.Key words: Phaseolus vulgaris, bean (small-seeded common), selection for yield, soil fertility, Middle American gene pools, regression coefficient

合成無機ポリマー中におけるＮ，Ｎ，Ｎ′，Ｎ′‐テトラメチル‐ｐ‐フェニレンジアミンカチオンラジカルの分子運動とＥＳＲスペクトル

The line width of each hfs line in ESR spectrum of a cation of N, N, N′, N′-Tetramethylpphenylenediamine (TMPD.+) formed in a mixture with butyl titanate polymer varies with the nuclear spin quantum number. Simulation of the ESR spectrum of TMPD.+ has been made using the line width which varies with nuclear spin quantum number. The contribution of τc(A-B) m1/h2 term to the line width was investigated to see which of the mIvalues, mI of benzene ring protons, mI, of methyl protons, or m, of nitrogen nuclei, is contributing most.The result indicates that the line width originating from the protons of the benzene ring is nearly 10 times as large as those coming from the protons of the methyl groups and the nitrogen nuclei. Therefore TMPID.+ in the butyl titanate polymer is considered to be fixed at the phenyl ring.

Investigation of CIDEP Effects of Hydrogen Radicals by Time Resolved ESR Spectroscopy

AbstractBy means of time resolved ESR spectroscopy the CIDEP effects of hydrogen radicals produced by pulse radiolysis of aqueous solutions were investigated. The quantitative analysis of the ESR time profiles of both H atom hfs lines and of D atom hfs lines based on the modified Bloch equations allows us to determine the spin relaxation times T1 and T2, the chemical life time τH and the initial and recombination polarizations PA, PA. While the relaxation rates T and T and the reciprocal of the life time τH−1 are proportional to the H radical concentration the recombination polarization PR is independent on the H atom concentration but shows an asymmetric behaviour to the spectrum centre. This asymmetry can be attributed to the ST0‐ and ST−1‐polarization of F pairs. – The experimental polarization parameters were compared with the theoretical results obtained from the stochastic Liouville equation by Pedersen and Freed. By this comparison the following quantities can be determined: The exchange interaction J(d) at the distance of closest approach of two H radical without recombination, The distance d of closest approach without use of the Smoluchowski relation and The number of radical pairs in the spur of water radiolysis including the probability of triplet and singlet precursors of direct produced H atoms in water radiolysis.

Hyperfine and isotopically invariant parameters of the GeS microwave spectrum

The complete set of microwave data for the nine isotopic species of the GeS molecule, available in literature, is reduced to molecular parameters by a nonlinear least-squares fit. All the hfs lines due to 73Ge ( I = 9 2 ) and 33S ( I = 3 2 ) are included in this fit. Watson's expressions of Dunham coefficients, including corrections to the Born-Oppenheimer approximation, are used. Contributions from off-diagonal terms are taken into account in the hfs Hamiltonian which is numerically diagonalized. A set of 12 hyperfine and isotopically invariant parameters is obtained and compared with previous determinations. It is shown that the accuracy of the hfs parameters is improved by one order of magnitude by the global treatment of all the data.

The reason for additional HFS at g ≅ 4.3 in the Mn 2+ EPR line in chalcogenide glasses

A model is proposed for the interpretation of the complex HFS at the Mn 2+ EPR line with the effective g-factor of about 4.3 This model attributes the additional HFS line to the forbidden hyperfine transitions. The expressions for the deviation of the g-factor at the lowest Kramers doublet from isotropy are obtained. Estimations of the forbidden transition probabilities due to different physical reasons are given. Some experimental regularities are discussed for a number of glass systems.

Two Dilute-Mn Salts Studied by ESR at Very Low Temperatures

In a temperature region down to 70 mK, the ESR spectra from Mn ++ doped in Zn(NH 4 ) 2 (SO 4 ) 2 ·6H 2 O and ZnSiF 6 ·6H 2 O have been observed. Unequal intensity of the six hyperfine structure (hfs) lines within a fine structure (fs) component reflecting the polarization of Mn nuclei, gives the nuclear spin temperature, T n , of the specimen. Only one fs component surviving at low temperatures, per one kind of ions, gives the fs constant, D , of positive sign for the former salt and that of negative for the latter. At slightly increased temperatures, lines belonging to the other fs components become observable, the intensity of which gives the electron spin temperature, T e . The thermometry using these spectra, applicable to a range down to 8 mK, is described, together with the enhancement in intensity caused by the polarization.

ESR Studies of Reduced Molybdovanadophosphoric Heteropoly Acids. II. Homogeneous Reduction

Abstract ESR spectra of the chemically reduced molybdovanadophosphoric heteropoly acids (H3+xMo12−xVxPO40·nH2O, where x=1 and 2) were observed in the solution and glassy state in various organic solvents. On addition of equimolar amounts of reductants such as SnCl2·2H2O, HSCH2CH2SH, and CH3SCH3, a transient ESR signal(B) appeared with eight hfs lines referred to as V(IV), I=7⁄2, and with <g>=1.96 and <T>=−0.83×10−2cm−1. However, it disappeared within ca. 5 hr at 20°C and another signal(C) with <g>=1.962 and <T>=−1.00×10−2 cm−1 gradually increased in intensity. The hyperfine coupling constant of the transient species was thus unusually small as compared with that of the ordinary V(IV) species and the C species. The mechanistic pathways of the reduction were discussed. The splitting observed in the low-field parallel components of the B signal was satisfactorily explained by a “geometrical charge isomerism” characteristic of the structure of the heteropoly anion. The origin of the unusually small hfs constant was discussed in the light of its molecular structure.

ESR of a dilute-Mn tutton salt around 0.1 K

Only one fine structure component with six hfs lines remains to be observed at the lowest temperature region, showing the sign of D to be positive. The intensities of its hfs lines are not equal reflecting the polarization of Mn nuclei and can be used as a thermometer down to 8 mK.

Observation of FeAl clusters in Alnico-type alloys by Mössbauer spectroscopy

Mossbauer spectra of highly coercive alloys Alnico 8 and Alnico 8X have been studied in a temperature range of 4.2 to 400 °K and in an external magnetic field of 42 kOe at 4.2 °K. At low temperatures two systems of HFS lines have been related to the strongly magnetic and weakly magnetic phases of the alloys. It is ascertained that Fe atoms in the weakly magnetic phase are in a ferromagnetic cluster of Fe3Al type passing into a superparamagnetic state when the temperature rises. A model alloy identical in composition to the weakly magnetic phase of Alnico 8 was also investigated and two kinds of clusters (ferromagnetic and non magnetic of Fe3Al and FeAl type, respectively) are found. The causes of the formation of non magnetic clusters in a model alloy are discussed. [Russian text ignored].

Direct detection of free radicals by EPR method during the polymerization of compounds of the acetylenic series

When the thermal bulk polymerizat ion of phenylacetylene, diphenylacetylene, p-iodophenylacetylene, phenoxyacetylene and diphenylbutadiyne (DPBD) is ca r r i edou t directly in an EPR spec t romete r at 150 o an intense EPR signal is observed immediately. In all cases , with the exception of DPBD, the EPR signal represen ts a single absorption line with a g factor that is close to the g factor of a free electron. In the polymerizat ion of DPBD the EPR signal has a hyperfine s t ruc ture (HFS) that consists of at least four lines, with a splitting of 35 Oe between the ext reme components. The two middle HFS lines are masked by an intense central signal, which has the same nature as the single absorption line in polyphenylacetylene, polydiphenylbutadiyne, and other polymers containing a conjugation system. Since the EPR signal disappears when the mater ia l is cooled to a t empera ture where the polymerizat ion of the corresponding monomer fails to occur , and the process is inhibited by N,N-diphenylpicrylhydrazyl , it may be assumed that we were the f i rs t to use the EPR method to direct ly detect the free radicals that take part in the polymerizat ion of c o m pounds of the acetylenic se r i es .

ESR Studies on Pyrolyzed and Irradiated Polyacrylonitrile

ESR studies are carried out at temperatures from 77 to -196°C for polyacrylonitrile (PAN) pyrolyzed in the temperature up to 700°C and for the one irradiated with ultraviolet light and γ-ray. The ESR spectra for PAN pyrolyzed below 600°C are considered to be due to a free radical because they are independent of the measurement temperature. The g-values are found to decrease with increasing pyrolysis temperature and a possible explanation is proposed. The ESR spectra for PAN pyrolyzed above 650°C are sensitively affected by being exposed to air and change with the measurement temperature in a complicated way; the broad and narrow lines are observed and it may be speculated that the former and latter are, respectively, due to a conduction electron and a free radical. For PAN irradiated with ultraviolet light and the one with γ-ray, hyperfine structure (hfs) is observed in the ESR spectra in contrast with those for pyrolyzed PAN. The hfs lines are well explained by two types of free radical likely to be produced.

Electron Spin Resonance in Ti-Doped VO2

The behavior of carriers trapped around doped Ti ions in VO 2 is investigated by means of the electron spin resonance in a temperature range between liquid nitrogen and room temperature. The line shapes are examined for different concentration of Ti. At lower concentration well resolved hyperfine lines are observed and a broad background line is superposed to them. With increasing impurity concentration, however, the single broad line grows up and the hfs lines diminish. At higher concentration only a single broad line of the Lorentz type is observed. The temperature dependences of the linewidth and the intensity for the hfs and broad lines are measured. The width of the broad line which does not vary at low temperature starts to increase at a temperature above which the intensity deviates from the Curie law. The motion of carriers localized around Ti impurity centers is discussed from these results.

Spacing of the hyperfine sextet in Mn 2+ ESR in LiNbO 3

An unusual feature that the Mn 2+ hfs lines in the M = 1 2 → − 1 2 transition are more widely spaced in the lower field has been observed in ferroelectric LiNbO 3. These spacings could be well explained by taking a large initial splitting into account.

Nuclear Spin and Moment ofAg110mby Paramagnetic Resonance

Paramagnetic resonance was observed in 253-day ${\mathrm{Ag}}^{110m}$, present as ${\mathrm{Ag}}^{2+}$ in the ${[{(\mathrm{i}\mathrm{s}\mathrm{o}\ensuremath{-}{\mathrm{C}}_{3}{\mathrm{H}}_{7})}_{2}\mathrm{NC}{\mathrm{S}}_{2}]}_{2}$Ag complex. Eleven hfs lines were observed, the positions of the other two lines being obscured by other absorptions present in the sample, and the nuclear spin of 6 was confirmed. A hfs constant ${a}_{110m}=(7.108\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ was determined. A hyperfine anomaly of ${\ensuremath{\Delta}}_{107,109}=\ensuremath{-}0.40%\ifmmode\pm\else\textpm\fi{}0.1%$ was observed for stable ${\mathrm{Ag}}^{2+}$ in this complex, indicating that the hfs arises from contact interaction. A nuclear moment of ${\ensuremath{\mu}}_{110m}=+3.55\ifmmode\pm\else\textpm\fi{}0.04$ nm was derived after a 3.7% hyperfine-anomaly correction. It is pointed out that hyperfine anomalies can be infinitely large for very small moments, and that the anomaly may cause a finite moment to exhibit vanishing hyperfine structure or conversely. The nuclear moment does not agree with shell-model predictions using empirical $g$ factors, being low by 1 nm. It is suggested that the ${({g}_{\frac{9}{2}})}^{7}$ proton configuration might be coupled to spin $\frac{7}{2}$. This yields a moment of +3.54 nm. The hyperfine fields for Ag in Fe and Ni are corrected to -282\ifmmode\pm\else\textpm\fi{}20 kG and -87\ifmmode\pm\else\textpm\fi{}8 kG, respectively.

ESR Study of Thio-indigo and Related Free Radicals

Thio-indigo and various Cl, Br, CH3, OCH3, OC2H5, and C6H5 derivatives were converted into free radicals. The electron spin resonance of these radicals in acetone was studied under low and high resolution. The width at maximum slope of the unresolved spectrum is about 6 G. The spectra, consisting of hfs lines of 0.07–0.2 G width at a spacing of 0.1–0.4 G, could be consistently analyzed. The relative unpaired-electron spin-density distribution in this type of molecule was determined. Cl and Br substituents do not give rise to observable splittings. Hyperconjugation appears to be effective for methyl substituents. For methoxy, ethoxy, and phenyl substituents a splitting due to the protons of these groups was found. The effect of substitution on observable electron spin densities is discussed.