溶液中(RC2R')Co(CO)(PR″3)2的配体PR″3之间的交换作用——三跳动力学模型

本文成功地运用了三跳动力学模型,通过相关函数和超精细分裂常数的关系, 推出了电子自旋共振波谱的线宽与基本线宽T_(2,0)~(-1)、溶液中各种异构体的超精细分裂常数、配体的交换寿命等之间的关系。求出了在290 K温度下(Ph_2C_2)Co(CO)[P(OEt)_3]_2的THF溶渡中P(OEt)_3配体的交换寿命是5.6×10~(-11)秒。     

Nuclear hyperfine splitting in the BX electronic band system of 127I2

The spacings between seven hyperfine components in the R(127) line of the 11-6 band of the B-X electronic transition of ¹²⁷I₂ are fitted, with a standard deviation of 17.3 kHz, by varying the nuclear quadrupole coupling constants eqQ′ and egQ′', the magnetic spin—rotation constant C_I and the tensor and scalar nuclear spin—spin coupling constants d′ and a′ in the hyperfine hamiltonian. The P(13) line of the 430 band is also analysed using an identical hamiltonian and a standard deviation of 6.25 kHz is obtained. No evidence for a magnetic octupole coupling is found to the precision of the data although this effect was invoked by Hackel et al. for the P(13) line.     

Hyperfine effects on collisional line shape. I. A self-consistent set of equations

We show that the treatment available in the literature for calculating hyperfine effects on collisional line shape is affected by an error making the theory not self-consistent. By correcting such an error we show that the two hyperfine effects on the line shape, modification of the resolved components and collisional coupling between them, cancel each other when hyperfine structure collapses into a single line.     

Stark effect measurement on Ca79Br X2Σ+

Using a molecular beam laser—microwave double resonance experiment, high-precision Stark effect measurements were performed on the electronic and vibrational ground state of Ca⁷⁹Br. The dipole moment was determined to be μo = 4.364(20)D. Furthermore the use of labeling techniques has been demonstrated in which a ground-state rotational transition is induced to label a specific hyperfine component of an optical emission line.     

Hyperfine effects on spectral line shape. II. The case DCO+-He

We discuss the hyperfine effect on the shape of rotational spectral lines of DCO(+) broadened by collisions with helium. Hyperfine scattering matrix is calculated by the recoupling technique from the spin-free scattering matrix which is obtained by close-coupling calculations and by a previously tested potential. Line shape is calculated for different rotational transitions, perturber density values, and collisional energies. As forecast by a semiclassical treatment and contrary to what may happen for a symmetric top absorber, hyperfine effects are small for a linear absorber. In our case they are of about 2%. We could also verify that the two hyperfine effects on the line shape, modification of resolved components and collisional coupling between them, cancel each other at high values of helium density when hyperfine structure collapses into a single line.     

Atomic spectral overlaps: A mathematical model and its use for studying line shape parameters

A mathematical model which describes an atomic spectral overlap is presented. The model is developed using hyperfine structure, overlap separation values, and line broadening calculations coupled with relative absorbance measurements of overlap and non-overlap situations. With good hyperfine structure data, the model can be used to determine the a-parameter values for both transitions of the overlap. Even in the absence of high quality data, the model can provide meaningful insights into line shapes, hyperfine structure, and wavelength assignments of overlapping spectral transitions.     

Spectral measurement of the caesium D2 line with a tunable heterodyne interferometer

The optical properties of a caesium atomic beam driven on a resonant hyperfine transition in the D₂ line were studied as a function of the probe laser frequency. Using a third off-resonant laser system, a heterodyne interferometer allowed simultaneous absorption and phase shift measurements of either the probe or the coupling laser. The signal features of the probe and coupling laser transmitted intensities showed strong differences in the vicinity of the hyperfine transitions excited by the probe laser. Regular absorption signals and electromagnetically induced transparency were found in either transmitted intensities. Furthermore, light induced birefringence of the probe laser was measured.     

Semiempirical theory of Carver rates in alkali/noble-gas systems

During an encounter between a noble-gas atom and an alkali-metal atom, the electron density at the alkali nucleus is altered, resulting in a collisional change in the alkali's hyperfine coupling (i.e., AI.S-->(A+deltaA)I.S). In the case of binary encounters, this process has been termed the Carver mechanism. The short-lived collisional change in hyperfine coupling can have very noticeable effects: it plays an important role in the loss of nuclear spin polarization in high magnetic fields, and it can be one of the dominant line broadening mechanisms for alkali hyperfine transitions (e.g., in atomic clocks). Unfortunately, though there have been measurements of the Carver relaxation rate, to date there has been little theoretical analysis of the Carver mechanism, in large part due to the very difficult problem of computing deltaA. In the present work, the author develops a theory of the Carver rate based on a semiempirical expression for deltaA(r)/A, where r is the internuclear alkali/noble-gas separation, and validates the theory by comparing to experiment. This model is then used to compute Carver and Bouchiat relaxation rates (i.e., the three-body sticking-collision analog of the Carver rate) in diverse/alkali-noble gas systems. The main conclusion of this work is that Carver rates vary by orders of magnitude across the alkalies, and in general will likely only play a significant role for Rb and Cs noble-gas systems.     

Oximetry of oxygen supersaturated solutions using nitroxides as EPR probe

The broadening of the three hyperfine EPR nitroxide lines in oxygen supersaturated solutions was examined. The solutions were supersaturated with oxygen either by thermal decomposition of 1,4-peroxy-1,4-dimethylnaphthalene or by pressurizing molecular oxygen above the sample solution. The linear relationship between the Lorentzian component of the line width and the O(2) concentration was proven to hold even when the hyperfine splitting is unresolved. In this region of line broadening, the requirement for spectral simulation is discussed.     

Hyperfine structure of the 625 nm band in the a 3Πu ← X 1 Σg transitions of Na2

Hyperfine structures of transitions in the a ³Π_u ← X¹Σ_g system of Na₂ have been accurately measured by Doppler-free laser excitation spectroscopy in a collimated molecular beam. The hyperfine patterns are quantitatively explained and the reduced matrix elements of the magnetic dipole hf interaction determined from a least-squares fit to the measured line positions.     

Xe nuclear magnetic resonance line shapes in channels decorated with paramagnetic centers

To make predictions of the Xe NMR line shapes for Xe in channels decorated with paramagnetic centers, we consider a model system using the O(2) molecule as the paramagnetic center. The previously calculated quantum mechanical Xe@O(2) hyperfine tensor for various configurations of Xe in the presence of O(2) provides a model for the hyperfine response of Xe atom to the presence of a paramagnetic center. The averaging is carried out using the same grand canonical Monte Carlo methodology as for calculating NMR line shapes for Xe in diamagnetic channels, modified to include the effects of the hyperfine tensor response. We explore the temperature dependence of the Xe line shapes, the dependence on the concentration, and the symmetry of distribution of embedded paramagnetic centers, on the orientation of the paramagnetic center axis with respect to the channel axis, and on the radial distance of the paramagnetic center from the axis of the channel. We predict Xe line shape signatures of the presence and orientation of paramagnetic centers and deduce which tensor elements provide measures of concentration and radial distance of paramagnetic centers from the channel axis.     

Line widths in nitroxides

The 2,5-di-tert-butyl-3,4-dimethoxycarbonyl-pyrryloxyl radical has the small est line-width and the smallest nitrogen hyperfine splitting reported for a stable nitroxide. The influence of long range proton splittings was shown by selective and total deuteriation. As expected on theoretical grounds, line widths and nitrogen hyperfine splitting are correlated.     

Author index to volume 91

The refocusing of a molecular beam of CaBr X²Σ⁺ by an electric quadrupole is investigated. The enhancement by electric deflection of the intensities of lines originating from levels of low J in the fluorescence excitation spectrum of CaBr B²Σ⁺ ?X²Σ⁺ is shown to be a useful technique of line assignment in a dense electronic band system. It is also found that the hyperfine levels are not transmitted equally through the quadrupole; for f levels, the hyperfine populations are actually reversed. A qualitative explanation, based on the correlation of zero-field hyperfine levels with high-field states, is given.     

1H-,2H-,13C- and 14N-endor studies of coppinger's radicals in liquid solutions and in liquid crystals

Proton and non-proton ENDOR studies are reported on isotopically labelled Coppinger's radical (galvinoxyl) and on N-Coppinger's radical in isotropic solutions and in liquid-crystalline mesophases. The hyperfine coupling constant shifts have been measured over the temperature range of the nematic mesophase and an analysis of the shifts in terms of anisotropic hyperfine tensors and ordering parameters is given. A short phenomenological discussion of the ¹³C and¹⁴N ENDOR response is presented. Several methods for the sign determination of hyperfine coupling constants are discussed. Finally, a survey of the ENDOR spectroscopy on galvinoxyl type biradicals is given.     

Magnetic resonance tracking of copper ion fixation on the surface of carboxylated nanodiamonds from viewpoint of changes in carbon-inherited paramagnetism

Detonation nanodiamonds with a particle size of 5 nm and a carboxylated surface are easily modified by doubly charged copper ions to form copper chelate complexes. The concentration of copper complexes in a dry powder of such nanodiamonds is well monitored by the method of electron paramagnetic resonance, both by the signal width of intrinsic paramagnetic centers in nanodiamonds and by the signal shape for the surface Cu²⁺ ions themselves, including the set of hyperfine splitting lines for the parallel component and the line with an unresolved hyperfine structure for the perpendicular component.     

Calculating the electron paramagnetic resonance parameters of exchange coupled transition metal complexes using broken symmetry density functional theory: application to a MnIII/MnIV model compound

The capability of the density functional broken symmetry approach for the calculation of various EPR parameters of exchange coupled metal clusters is demonstrated by studying the experimentally well-investigated [Mn(III)Mn(IV)(mu-O)(2)(mu-OAc)DTNE](2+) complex. Geometry optimizations of the complex in its broken symmetry and high spin states yielded structures with two distinct manganese sites and geometrical parameters in good agreement with the X-ray structure. Exchange coupling constants were calculated from the energy differences between the high spin and broken symmetry states using the Heisenberg spin Hamiltonian. Very good agreement between theory and experiment was achieved with the B3LYP hybrid functional. The g-tensor calculations were performed employing the coupled perturbed Kohn-Sham equations. A strategy for the computation of g-tensor site values is presented and provides single-site g-tensors that are in good agreement with the expectations for Mn(III) and Mn(IV), respectively. Spin projection gave the g-tensor of the coupled manganese complex in very good agreement with the experimental results. Complete (55)Mn hyperfine tensors, including spin-orbit contributions, were calculated and spin-projected. The source of anisotropy in this system could be traced back to the Mn(III) ion in line with the experimental results. The isotropic manganese hyperfine coupling constants were underestimated by factors between 1.4 and 2.5. It is shown that this deficiency is systematic in character and not anchored in the broken symmetry approach. Nuclear quadrupole splitting of the (55)Mn nuclei is shown to be small in this system. In addition, (14)N and (1)H ligand hyperfine data were calculated and compared well with the experimental results. The quality of the extended point-dipole model was demonstrated in application to (1)H anisotropic hyperfine coupling constants.     

Needs for fundamental atomic reference data and data distribution: applied analytical spectroscopy - Response to a questionnaire

Results of a survey of the needs for fundamental data of analytical spectroscopists are pointed out with special reference to applied analytical spectroscopy. Wavelengths, energy levels, level assignments, physical line widths, line shifts, and hyperfine structure are covered. Ways for dissemating fundamental data tabulations to the analytical community are also discussed.     

Hyperfine structure of some near-infrared Xe I and Xe II lines

This work reports on the experimental determination of the hyperfine splitting of the Xe I lines at 828.01 nm and 834.68 nm and the Xe II line at 834.72 nm. Measurements were performed by means of Doppler-free saturation spectroscopy in a low-pressure radio-frequency discharge. The absolute wavelength of all hyperfine components is obtained by way of a high-precision wavemeter backed-up with the absorption spectrum of the NO₂ molecule. We provide an accurate estimate of hyperfine constants for the lower level of the Xe II transition at 834.72 nm. The two Xe I transition outcomes of our experimental study are compared with data available in the literature.     

Observation of quadrupole hyperfine structure in the v6 RQ3 (6) transition of 12CH335Cl

Quadrupole hyperfine structure has been observed in the v₆^RQ₃(6) transition of ¹²CH₃³⁵Cl using a stable CO₂ laser oscillating on the 9.4 μm P(26) line. By heterodyning this laser with another which is locked to the 4.3 μm fluorescence dip of the 00⁰1-00⁰ CO₂ transition, an accurate measurement of the hyperfine splittings has been made. The observed spectrum agrees, within experimental error, to the theoretical values evaluated without the need for a vibrational correction to the quadrupole interaction in the excited vibrational state. The hyperfine component closest to the center of the CO₂ P(26) transition is determined to be 5.6 ± 0.1 MHz from the P(26) line center.     

Hyperfine structure observed in EPR spectra of polyphenylacetylene solutions

The high-temperature (>120C) electron paramagnetic resonance (EPR) spectrum of solutions of polyphenylacetylene have been deconvoluted into the spectra of two separate radicals, a delocalized π radical, whose EPR spectrum consists of a single 15-G wide Gaussian line comprising about 90% of the total signal and a second, more localized π radical exhibiting complex hyperfine structure in its EPR spectrum. Some possible structures for the minor component radical are suggested and their hyperfine splitting constants calculated using molecular orbital theory.