Unresolved Hyperfine Structure Research Articles

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.

Anomalous light-induced broadening of the spin-noise resonance in cesium vapor

We uncover a highly nontrivial dependence of the spin-noise (SN) resonance broadening induced by the intense probe beam. The measurements were performed by probing the cell with cesium vapor at the wavelengths of the transition $6^{2}S_{1/2}\ensuremath{\leftrightarrow}6^{2}P_{3/2}$ (${D}_{2}$ line) with the unresolved hyperfine structure of the excited state. The light-induced broadening of the SN resonance was found to differ strongly at different slopes of the ${D}_{2}$ line and, generally, varied nonmonotonically with light power. We discuss the effect in terms of the phenomenological Bloch equations for the spin fluctuations and demonstrate that the SN broadening behavior strongly depends on the relation between the pumping and excited-level decay rates, the spin precession, and decoherence rates. To reconcile the puzzling experimental results, we propose that the degree of optical perturbation of the spin system is controlled by the route of the excited-state relaxation of the atom or, in other words, that the act of optical excitation of the atom does not necessarily break down completely its ground-state coherence and continuity of the spin precession. Spectral asymmetry of the effect, in this case, is provided by the position of the ``closed'' transition $F=4\ensuremath{\leftrightarrow}{F}^{\ensuremath{'}}=5$ at the short-wavelength side of the line. This hypothesis, however, remains to be proven by microscopic calculations.

Resonant two-photon spectroscopy of the 2s3d 1D2 level of neutral Be9

We report an absolute frequency measurement of the $2s3d{\phantom{\rule{0.16em}{0ex}}}^{1}{D}_{2}$ state in neutral $^{9}\mathrm{Be}$ using two-photon spectroscopy with a resonant intermediate state. The absolute center-of-gravity energy is determined to be 64 428.40 321(55) ${\mathrm{cm}}^{\ensuremath{-}1}$, a factor of 180 more precise than the previous experimental measurement. We also confirm our previous result for the energy of the intermediate $2s2p{\phantom{\rule{0.16em}{0ex}}}^{1}{P}_{1}$ level. Precision is limited by unresolved hyperfine structure and the complications of performing resonant two-photon spectroscopy on an atomic beam. A three-level rate-equation analysis is presented to explore, and minimize, systematic uncertainties arising from small deviations of the angle between the atomic and optical beams off-perpendicular.

Numerical analysis of the optical pumping process coupled with 23Na D2 manifold modeled as a partially resolved hyperfine structure

All magnetometers using alkali atoms rely on the monochromatic light driving the optical pumping process in the D1 or D2 line to create spin-polarized atoms. In the study of a sodium (Na) magnetometer, we find that 23Na exhibits the same hyperfine structure as exhibited by the 87Rb atom but differs from Rb in terms of level splitting. The narrowly split hyperfine levels of the 23Na 3P3/2 excited state are comparable to its natural broadening (9.8 MHz). We have modeled the nearly unresolved hyperfine structure as a partially resolved multilevel system in which the absorption at each photon detuning will induce adjacent allowed transition pathways simultaneously. Thus, the corresponding optical pumping processes of 23Na and 87Rb are governed by similar rate equations but result in different redistributed populations. By numerically solving the rate equations, we demonstrate that optically pumped 23Na has a much smaller spin polarization than that of 87Rb because the population imbalances between the ground state Zeeman levels of 23Na are very small. The inefficient optical pumping can explain why Na magnetometers are not studied extensively. The investigation into the optical pumping process of 23Na is helpful in preparing a highly spin-polarized atomic medium and optimizing the sensitivity of Na magnetometers.

Erratum to: A Simple Analytical Approximation to an Inhomogeneously-Broadened Dispersion Spectrum. Application to Absorption-Dispersion Admixtures.

A simple analytical approximation to an inhomogeneously-broadened dispersion signal is proposed and tested with resonance lines broadened by unresolved hyperfine structure. Spectral parameters may be rapidly and accurately extracted using a nonlinear least-squares fitting algorithm. Combining the new approximation to a dispersion signal with a well-known approximation to the absorption signal allows dispersion-absorption admixtures, a problem of growing importance, to be analyzed quickly and accurately. For pure dispersion signals, the maximum difference between the fit and the signal for unresolved lines is 1.1 % of the maximum intensity. For pure absorption, the difference is 0.33 % of the peak-to-peak intensity, and for admixtures up to 40 % dispersion (maximum intensity/peak-to-peak intensity), the difference is 0.7 %. The accuracy of the recovered spectral parameters depends on the degree of inhomogeneously-broadened and the percentage admixture, but they are generally about 1 % at most. A significant finding of the work is that the parameters pertinent to the dispersion or the absorption are insignificantly different when fitting isolated lines vs. fitting admixtures. Admixtures with added noise or an unsuspected extraneous line are investigated.

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

Recently we reported a high-precision optical frequency measurement of the (v, L): (0, 2)rightarrow(8, 3) vibrational overtone transition in trapped deuterated molecular hydrogen (HD+) ions at 10 mK temperature. Achieving a resolution of 0.85 parts-per-billion (p.p.b.), we found the experimental value [ν0 = 383, 407, 177.38 (41) MHz] to be in agreement with the value from molecular theory [νth 383, 407, 177.150 (15) MHz] within 0.6 (1.1) p.p.b. (Biesheuvel et al. in Nat Commun 7:10385, 2016). This enabled an improved test of molecular theory (including QED), new constraints on the size of possible effects due to ‘new physics,’ and the first determination of the proton–electron mass ratio from a molecule. Here, we provide the details of the experimental procedure, spectral analysis, and the assessment of systematic frequency shifts. Our analysis focuses in particular on deviations of the HD+ velocity distribution from thermal (Gaussian) distributions under the influence of collisions with fast ions produced during (laser-induced) chemical reactions, as such deviations turn out to significantly shift the hyperfine-less vibrational frequency as inferred from the saturated and Doppler-broadened spectrum, which contains partly unresolved hyperfine structure.

A Simple Analytical Approximation to an Inhomogeneously-Broadened Dispersion Spectrum. Application to Absorption-Dispersion Admixtures.

A simple analytical approximation to an inhomogeneously-broadened dispersion signal is proposed and tested with resonance lines broadened by unresolved hyperfine structure. Spectral parameters may be rapidly and accurately extracted using a nonlinear least-squares fitting algorithm. Combining the new approximation to a dispersion signal with a well-known approximation to the absorption signal allows dispersion-absorption admixtures, a problem of growing importance, to be analyzed quickly and accurately. For pure dispersion signals, the maximum difference between the fit and the signal for unresolved lines is 1.1 % of the maximum intensity. For pure absorption, the difference is 0.33 % of the peak-to-peak intensity, and for admixtures up to 40 % dispersion (maximum intensity/peak-to-peak intensity), the difference is 0.7 %. The accuracy of the recovered spectral parameters depends on the degree of inhomogeneously-broadened and the percentage admixture, but they are generally about 1 % at most. A significant finding of the work is that the parameters pertinent to the dispersion or the absorption are insignificantly different when fitting isolated lines vs. fitting admixtures. Admixtures with added noise or an unsuspected extraneous line are investigated.

Hyperfine structure effects in Doppler-broadening thermometry on water vapor at 1.4 μm

This article builds upon a previous work dealing with the budget of uncertainties associated to our recent determination of the Boltzmann constant by means of Doppler broadening thermometry. We report on the outcomes of theoretical calculations and numerical simulations aimed to precisely quantify the influence of the unresolved hyperfine structure of a given ortho component of the O spectrum at 1.4 μm on the measurement of the Doppler width of the line itself. We have found that, if the hyperfine structure of the line of the band was ignored, the spectroscopic measurement of the Boltzmann constant would be affected by a relative systematical deviation of .

Revealing the Cu2+ ions localization at low symmetry Bi sites in photorefractive Bi12GeO20 crystals doped with Cu and V by high frequency EPR

The sites of incorporation of Cu2+ impurity ions in Bi12GeO20 single crystals co-doped with copper and vanadium have been investigated by electron paramagnetic resonance (EPR). While the X-band EPR spectra consist of a simple broad (ΔB ∼50mT) line with anisotropic lineshape, the W-band EPR spectra exhibit well resolved, strongly anisotropic lines, due to transitions within the 3d9–2D ground manifold of the Cu2+ ions. The most intense group of lines, attributed to the dominant Cu2+(I) center, displays a characteristic four components hyperfine structure for magnetic field orientations close to a 〈110〉 direction. The g and A tensor main axes are very close to one of the 12 possible sets of orthogonal 〈1−10〉, 〈00−1〉 and 〈110〉 crystal directions. Several less intense lines, with unresolved hyperfine structure and similar symmetry properties, mostly overlapped by the Cu2+(I) spectrum, were attributed to Cu2+(II) centers. The two paramagnetic centers are identified as substitutional Cu2+ ions at Bi3+ sites with low C1 symmetry, very likely resulting from different configurations of neighboring charge compensating defects.

Electron Paramagnetic Resonance Study of Copper–Ethylenediamine Complex Ion Intercalated in Bentonite

This work reports on studies of two-dimensional networks of Cu2+ ions, built by exchanging Na-bentonite with Cu2+ aqueous or with the bis(ethylenediamine) complex, [Cu(C2H4 (NH2))2]2+, at different concentrations of the paramagnetic center. Dilution of the magnetically active species is performed by the cointercalation of analogous diamagnetic zinc species, aqueous Zn2+, or complexed [Zn(C2H4 (NH2))2]2+ ions, with ethylenediamine in excess. Materials were characterized by X-ray diffraction, Fourier transform infrared (FT-IR) and UV–visible spectroscopy, and continuous-wave electron paramagnetic resonance (EPR). X-ray diffraction measurements indicated that the interlaminar distance in the bentonite decreases with the increase of Zn concentration in the composites. The observation of a two-component Cu2+ EPR spectrum imply the coexistence of isolated Cu2+ with a well-resolved hyperfine structure and spin–spin exchanged Cu2+ dimers or clusters with an unresolved hyperfine structure. EPR spin Hamiltonian parameters of the isolated species in Cu/ethylenediamine intercalated samples are typical of axially distorted sites, six-coordinated with bis(ethylenediamine) in the equatorial plane and with oxygen on the internal surfaces of the clay. Experimental facts indicate that the interaction between paramagnetic centers is mainly favored by two different phenomena: turbostratic disorder of clay sheets and segregation of the magnetic centers leading to interstratifications of layers.

Electronic transitions of cobalt monoboride

Electronic transition spectrum of cobalt monoboride (CoB) in the visible region between 495 and 560 nm has been observed and analyzed using laser-induced fluorescence spectroscopy. CoB molecule was produced by the reaction of laser-ablated cobalt atom and diborane (B(2)H(6)) seeded in argon. Fifteen vibrational bands with resolved rotational structure have been recorded, which included transitions of both Co(10)B and Co(11)B isotopic species. Our analysis showed that the observed transition bands are ΔΩ = 0 transitions with Ω" = 2 and Ω" = 3 lower states. Four transition systems have been assigned, namely, the [18.1](3)Π(2)-X(3)Δ(2), the [18.3](3)Φ(3)-X(3)Δ(3), the [18.6]3- X(3)Δ(3), and the [19.0]2-X(3)Δ(2) systems. The bond length, r(o), of the X(3)Δ(3) state of CoB is determined to be 1.705 Å. The observed rotational lines showed unresolved hyperfine structure arising from the nuclei, which conforms to the Hund's case (a(β)) coupling scheme. This work represents the first experimental investigation of the CoB spectrum.

Paramagnetic centers in graphene nanoribbons prepared from longitudinal unzipping of carbon nanotubes

Electron spin resonance (ESR) investigation of graphene nanoribbons (GNRs) prepared through longitudinal unzipping of multi-walled carbon nanotubes indicates the presence of C-related dangling bond centers, exhibiting paramagnetic features. ESR signal broadening from pristine or oxidized GNRs is explained in terms of unresolved hyperfine structure, and in the case of reduced GNRs, the broadening of the ESR signal can be due to enhancement of conductivity upon reduction. The spin dynamics observed from ESR line width-temperature data reflect a variable range hopping mechanism through localized states, consistent with resistance-temperature data.

Design, construction, and testing of a large-cavity, 1-10 GHz Flygare-Balle spectrometer

A large pulsed-beam, Fourier transform microwave spectrometer employing 48 in. diameter mirrors and 35(") (NHS-35) diffusion pump has been constructed at the University of Arizona. The Fabry-Perot-type cavity, using the large mirrors provides Q-values in the 15,000 to 40,000 range. Test spectra were obtained using transverse and coaxial injection of the pulsed-nozzle molecular beams. The measured molecular resonance linewidths were 8 kHz for the transverse injection and 2 kHz for coaxial molecular beam injection. Good signal to noise ratios were obtained for the test signals. Strong lines for butadiene iron tricarbonyl were seen with a single beam pulse (S/N = 5/1). Transitions were measured as low as 900 MHz and some previously unresolved hyperfine structure is now resolved for the butadiene iron tricarbonyl spectra. The spectrometer is operated using a personal computer with LABVIEW programs, with provisions for automatic frequency scanning. The extended, low-frequency range of this spectrometer should make it very useful for making measurements on significantly larger molecules and complexes than have been previously studied. The improved resolution, in the coaxial beam mode, will allow better resolution of hyperfine structure. The large diffusion pump allows a higher beam pulse frequency to compensate for the generally lower sensitivity at lower frequencies.

Cavity ring-down spectroscopy measurements of sub-Doppler hyperfine structure

Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was used to measure magnetic dipole transitions in the $b {}^{1}$${\ensuremath{\Sigma}}_{g}^{+}$ $\ensuremath{\leftarrow}$ $X $${}^{3}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}$($0,0$) band of ${\mathrm{O}}_{2}$. The $^{17}\mathrm{O}$-containing isotopologues show unresolved hyperfine structure due to magnetic hyperfine splitting in the ground state. The sensitivity and stability of FS-CRDS allow for quantitative sub-Doppler measurements of the hyperfine constants, even when the hyperfine splittings are much smaller than the Doppler width. Unlike saturation spectroscopy, this linear absorption technique can be applied to weak transitions and employed to quantitatively measure intensities and line shapes. This method may be an attractive approach for measuring unresolved hyperfine structure in excited electronic states.

High sensitivity CRDS of the a1Δ g− X3Σg− band of oxygen near 1.27 μm: Extended observations, quadrupole transitions, hot bands and minor isotopologues

The CW-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of the a 1Δ g– X 3 Σ g − band of oxygen near 1.27 μm. The spectra were obtained between 7640 and 7917 cm −1 with “natural” oxygen and with a sample highly enriched in 18O. The absolute intensities of 376 and 643 oxygen transitions were measured in the two spectra. They include the a 1Δ g− X 3 Σ g − (0–0) bands of 16O 2, 16O 18O, 16O 17O, 17O 18O and 18O 2. The (0–0) bands of 16O 2 and 18O 2 show weak quadrupole transitions with line intensities ranging from 1×10 −30 to 1.9×10 −28 cm/molecule. They are accompanied by the a 1Δ g− X 3 Σ g − (1–1) hot bands, which are reported for the first time. The line profiles of the transitions of the 16O 17O and 17O 18O isotopologues were observed to be broadened due to an unresolved magnetic hyperfine structure. Accurate spectroscopic parameters of the different energy levels involved in the observed bands were derived from a global fit of the observed line positions, combined with microwave and Raman measurements available in the literature.

EPR and electronic spectral properties of aryl-substituted bis(dithiophosphato)copper(II) complexes

The spectral properties of bis(diaryl-dithiophosphato)copper(II) complexes, [Cu(S 2P(OR) 2) 2], with R = o-cresyl (complex I) and 2,6-dimethylphenyl (complex II) are studied by EPR- and vis spectroscopy. In solid (powder) state both complexes exhibit dark brown colour and are paramagnetic. Room temperature EPR spectra of the complexes dissolved in non-coordinating (C 6H 5CH 3, C 5H 12, C 6H 14), acceptor (CHCl 3, CCl 4) or donor (DMFA, DMSO) solvents have typical features of the chromofore CuS 4. In non-coordinating and acceptor solvents their isotropic EPR parameters are: g iso = 2.047 ± 0.003, Cu A iso = 7.2 ± 0.1 mT and P A = 0.95 ± 0.1 mT. An absorption band characterizes the vis spectra in these solvents with a maximum at 427 nm, due to a ligand-to-metal charge-transfer transition. One hour after dissolution the absorbance at 427 nm follows Beer's law with molar absorptivity ( ɛ) about 11 000, which does not change significantly after 24 h staying at room temperature or after 30 min heating at 50 °C. Both DMFA and DMSO exhibit specific solute–solvent interaction with the acceptor centre of copper complex yielding an axial adduct, with increased g-factor and decreased hf A compared to the initial complex. An additional EPR signal with unresolved hyperfine structure is also detected in DMSO. EPR and vis intensities of both bis(diaryl-dtp)Cu(II) complexes decrease after dissolution in both solvents. Moreover, they are EPR silent in pyridine and do not show any absorption in the vis spectra.

Stable free radicals in insect cuticles: Electron spin resonance spectroscopy reveals differences between melanization and sclerotization

Insect cuticles (exuviae; cast skins) were examined for the first time by ESR spectroscopy for the presence of stable free radicals, as found in melanins. All cuticles, except those from a locust albino strain, irrespective of the presence of melanin, provided single-line signals of varied g-values and linewidths. The ESR signals of melanins, isolated or in cuticles, were characterized by g-values <2.004 and small linewidths in the range of 4–6 G, while sclerotized cuticles, lacking melanin, showed g-values >2.004 and broad linewidths of 5–11 G. The melanin spectra were comparable to those reported for eumelanins with indol-based monomers. Minor signals ascribed to pheomelanins were found in several probes. The ‘sclerotin’ spectra were broader and displayed unresolved hyperfine structure in some cases. As for melanins, the location and environment of the radicals in cuticles giving rise to the two types of ESR spectra could not be assigned. Changes in the radical environment due to insecticide or solvent treatment can be detected by ESR spectroscopy.

Hyperfine structure and interstellar curves of growth

The effects of the hyperfine structure (HFS) that is present in some interstellar absorption lines are investigated in the case of a single absorbing cloud. If the respective total equivalent widths of two or more unresolved HFS multiplets measured in relatively low-resolution spectra are analysed specifically by means of a curve of growth, the column density N(X) and the linewidth parameter b(X) inferred for absorbing species X in the cloud will generally be in error if the HFS is ignored. The fundamental physical effect is the reduced line saturation that arises because the total column density is divided among the HFS levels of the ground atomic level, each of which generally gives rise to an HFS line at a different wavelength. For nuclear spins / = 3/2 and / = 5/2, theoretical curves of growth are calculated for some of the resonance lines of some alkali atoms, for each of four illustrative choices of the parameter α = A/b, the ratio of the HFS splitting in the ground atomic level to the linewidth. Applications of the results to interstellar absorption by NaI, KI and Al III are emphasized. HFS is, fortunately, unimportant for most interstellar lines, however. Among the 35 elements that have been detected in diffuse clouds via interstellar absorption in the ultraviolet/optical spectral region, the most abundant isotope of each of 25 of these shows no HFS, because I = 0 or, in the relevant ground atomic level, J = 0.

Apparent pressure shift of rotational transitions as a consequence of the unresolved hyperfine structure

Apparent pressure dependent shifting of the peak positions of rotational lines, which is a consequence of unresolved hyperfine structures, is analyzed. In addition, possible line profile asymmetries and their influences on the ultimately achievable measurement accuracy are discussed for rotational transitions of ammonia and acetonitrile. These effects are caused by partially overlapped, but unresolved line profiles of individual hyperfine components.

Hyperfine quantum beats from photolytic orientation and alignment

Using Doppler-resolved transient frequency modulation absorption spectroscopy, we have measured both alignment and orientation quantum beats arising from nuclear hyperfine depolarization of low rotational levels of CN X 2sigma+ photofragments produced in the ultraviolet photodissociation of ICN. Under our conditions of fully resolved fine-structure and completely unresolved hyperfine structure, the observed time evolution is insensitive to the rapid depolarization of angular momentum N that would be observed if the fine-structure components were not resolved. Non-statistical spin-rotation populations of CN photofragments, previously observed only for high rotational states, are now observed even for the lowest rotational states, indicating that the electron can not be considered a spectator spin in the depolarization.