Hyperfine Multiplet Research Articles

Vibration-rotation spectroscopy of the HD+ion near the dissociation limit

We have observed and measured five rotational components of the 21–17 band in the HD+ molecular ion. The highest bound rotational level in υ=21 is predicted to be N = 3, which lies only 1·8 cm−1 below the H++D dissociation limit, and we have observed transitions involving all four rotational levels of υ=21. The measured transition frequencies are close to those predicted by recent non-adiabatic calculations. Each vibration-rotation line is split into six hyperfine components, which arise primarily because of Fermi contact interactions with the proton and deuteron nuclei. Analysis of these hyperfine multiplets yields values of the Fermi contact hyperfine constants for the lower and upper states in each vibration-rotation transition. These values show that in υ=17 the electron distribution is essentially symmetric, but in υ=21 it becomes increasingly asymmetric as N increases. The proton Fermi contact hyperfine constant is close to 715 MHz in υ=17, but decreases to only 53 MHz in 21,3. Correspondingly the deuteron hyperfine constant increases from 112 MHz in υ=17 to 213 MHz in 21, 3, which is only slightly less than the free deuterium atom value of 218 MHz. These results demonstrate that in 21, 3 the electron is virtually localized at the deuteron, so that the molecule is perhaps best regarded as a long-range H+…D Langevin complex.

Nuclear-quadrupole effects in the pressure broadening of molecular lines.

We report the first experimental evidence of variable collision-broadening parameters within the hyperfine multiplet of a rotational line. A similar behavior is observed in the Stark pattern of one hyperfine line. All the experimental results, obtained on ${\mathrm{CH}}_{3}$I, are explained in terms of a theoretical model accounting for line coupling. The same approach is successful in interpreting the literature data for the Stark lines of ${\mathrm{CH}}_{3}$Br and previous null results for other molecules.

The Temperature Dependence of Spectral Broadening in the Hg (61S0-63P1) Multiplet At High Optical Densities.

A new method has been developed for determining rapidly changing translational temperatures in a gas that has been heated by such transient phenomena as the passage of a shock wave or the absorption of sub-microsecond pulses of radiation from an infrared laser. The method depends upon the use of trace amounts of Hg vapor and its absorption of radiation in the neighborhood of the 253.7 nm isotopic and hyperfine multiplet. As the Hg atoms sense changes in the translational temperature of the host gas, the absorption of 253.7 nm radiation also changes by virtue of the Doppler and Lorentz broadening of the multiplet lines. Emission spectra of a Hg discharge light source in the neighborhood of 253.7 nm were shown to be readily simulated by a two zone computer model even at large optical densities. The same lamp parameters that were used in these calculations could also be used to simulate the experimental pressure and temperature dependence of the total integrated absorption. This provided a means for obtaining the temperature calibration curves needed to monitor the changing translational temperature of a gas undergoing rapid heating or cooling.

Hyperfine structure and isotope shifts in odd-parity 6snp and 6snf Rydberg series of Ba I

Hyperfine structure and isotope shifts in transitions to odd-parity 6snp and 6snf Rydberg configurations of barium have been investigated using laser-atomic-beam spectroscopy. For the 6snf Rydberg configurations with n=13-42 the complete hyperfine multiplet is observed. The data on isotope shifts have been used to test the total perturber character mixed in the 6snp and 6snf Rydberg states predicted by existing multichannel quantum defect theory (MQDT) treatments of the odd-parity J=0, 1, 2, 3 and 4 spectra. The MQDT predictions are shown to be reliable in this respect. The hyperfine structure of the singlet and triplet states is analysed in terms of singlet-triplet mixing. The extracted mixing coefficients disagree with the predictions of existing MQDT models, even when an interaction between 'singlet' and 'triplet' 6snl channels is introduced. New MQDT models have been developed in which both energies and mixing coefficients are reproduced well. Hyperfine structure data provides information on interactions between mutually perturbing channels. Finally an earlier analysis of the hyperfine structure of the 6snf 3F states in terms of effective parameters is discussed.

Saturation of the 0-0 hyperfine-transition linewidth enhancement factor in optically pumped alkali-metal vapors.

In a previous publication [Phys. Rev. A 31, 1440 (1985)], we determined the linewidth enhancement factor (LEF) of the microwave-power-broadened linewidth of the 0-0 hyperfine transition in optically pumped alkali-metal vapors. This factor is essentially a measure of the ratio of the transition linewidth to the microwave Rabi frequency. In the previous study, optical pumping out of only one hyperfine multiplet was considered. In the present study, the expressions are generalized to include optical pumping out of both hyperfine multiplets simultaneously. Dramatic changes in the behavior of the LEF as a function of the optical-pumping rate are predicted.

Light-shift deviations observed in collinear laser-rf double-resonance spectroscopy.

The energy difference between two hyperfine levels of the ground state, measured with high precision by collinear laser-rf double-resonance spectroscopy, is influenced by the light shift, depending on the intensity and frequency of the laser field. We report on a measurement of the change in rf transition frequency between the F=2 and F=3 levels of the 5d ${\mathrm{}}^{2}$${D}_{3/2}$ hyperfine multiplet of $^{137}\mathrm{Ba}^{+}$ as a function of laser frequency. The observed results are in good agreement with theoretical calculations.

Effects of nuclear structure and triplet-singlet interaction in the 1s2s3S1 hyperfine multiplet of Li+

From combined laser-microwave spectroscopy of the 1s2s3S1 hyperfine structure (hfs) splittings in helium-like6,7Li+ ions, the magnetic dipole hfs interaction constantA and a small displacement σ of theF=1 substate, caused by 1s2s3S1−1s2s1S0 hyperfine mixing, have been obtained. Analysis ofA yields nuclear structure effects in the hfs splittings of the isotopes6,7Li+. The result of a calculation of6,7δ with accurate integral-transform 21S0 and 23S1 wave functions is presented.

Laser-microwave spectroscopy in the excited 1s2s3S1 and 1s2p3P hyperfine multiplets of helium-like6,7Li+

Laser-microwave spectroscopy in the excited 1s2s3S1 and 1s2p3P hyperfine multiplets of helium-like6,7Li+

35Cl Nuclear Quadrupole Interaction in Thionyl Chloride

Abstract 21 hyperfine multiplets, up to J = 12, have been measured for thionyl chloride (32S16O35Cl2), by means of microwave spectroscopy in the region 18.0 -26.5 GHz. Nuclear quadrupole coupling constants along the principal axes of inertia were determined to be χaa = - 25.004 ± 0.040 MHz, χbb = -0.009 ± 0.025 MHz and χcc = 25.013 ± 0.031 MHz. Also, coupling constants along the S-Cl bond axis (z axis) and two axes perpendicular to this have been calculated to be χxx = 65.93 MHz, /χyy = 30.36 MHz and χzz = -96.30 MHz. These values have been compared with those of other workers and with those of other related molecules. Information about the electronic distribution in the S-Cl bond has been obtained from the values of these constants, and the results have been discussed.

Electron-spin echoes and saturation in coal

Free radical electron paramagnetic resonance (e.p.r.) spectra of coal are comprised of unresolved hyperfine multiplets with widths of ≈770 kHz, ( T 2) −1, at 90–110 K. Unresolved hyperfine interactions are measured in the spin echo decay modulation and locate nuclei in the coal structure relative to the radical. With two distinguishable coal e.p.r. spectra in the sample, it is demonstrated that components may be separated from one another in the spin echo spectrum by judicious choice of temperature, pulse interval and echo repetition rate. The relaxation times T 1 and T 2 are measured with the spin echo at several temperatures.

Energy-level shift of5snsS13Rydberg states ofSr87

Doppler-free two-photon spectroscopy was applied to excite hyperfine-induced transitions from the $5{s}^{2}^{1}S_{0}$ ground state to the $F=I$ component of the hyperfine multiplet of the $5sns^{3}S_{1}$ Rydberg series of $^{87}\mathrm{Sr}$ ($n=50,\dots{},85$). The experimental data confirm the interpretation of hyperfine-induced singlet-triplet mixing which is related to the singlet-triplet energy separation.

The magnetic properties of the oxygen–hole aluminum centers in crystalline SiO2. III. [AlO4]+

The EPR spectra of [AlO4]+ have been measured in α-quartz at ca. 35 K after X-irradiation at 77 K. This center is believed to contain two electron holes, one at each of two symmetry-related oxygen ions bonded to an aluminum ion substituted for silicon, forming a triplet spin system. Measurements of the two primary 27Al hyperfine multiplets (Ms = 0 ↔ Ms = ± 1) as well as the quasi-forbidden multiplet (Ms = + 1 ↔ Ms = −1) at half field have been made, and have led to a spin-Hamiltonian (matrices [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]). A crystal two-fold axis contains the aluminum ion and relates the two-hole-bearing oxygen ions, as well as the two outer silicon ions bonded respectively to the latter. The electronic quadrupole matrix [Formula: see text] is attributed primarily to the magnetic dipole–dipole interaction between the two unpaired electrons. The results of a comparison among the matrices [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and the corresponding matrices for the related single-hole centers [AlO4]0 and [AlO4/M+]+ (where M = H, Li) are consistent with the model for [AlO4]+.

Multimode and level-degeneracy effects in two-step resonant photoionization processes

A theoretical model of two-step resonant ionization which includes an autoionizing state is developed. The effects examined include interactions with a multimode laser and Zeeman and hyperfine multiplets. We approach this problem starting from first principles by treating the atom-radiation system as a unit. Theoretical analysis and numerical calculations of ionization probabilities are given. The intermode scattering is investigated in detail, and a simple physical interpretation of the dynamical effect is given. Comparisons of ionization probabilities for two-step processes with first-step excitations by single-mode or two-mode lasers are made. It is found that, if the mode spacing in a multimode-laser beam is less than the Doppler width of the atom, the multimode laser can more effectively produce ions than a single-mode laser does. This leads to the conclusion that the resonance effect is more important than the power-broadening effect. This is shown to be also true when Zeeman and hyperfine multiplets are included.

Rotational energy transfer in collisions between orbitally non-degenerate open-shell systems

The theory is developed for the rotational energy transfer induced in an open-shell molecule by collision with an open-shell atom. The consequences of the exchange interaction between such systems are investigated and related to the behaviour of unpaired electron spins during inelastic collisions. The coupled equations for the closed shell case are first developed, and generalized equations derived for the matrix elements of a spin-independent potential. The spin-exchange interaction potential of open-shell species is then expressed in a form suitable for scattering theory and this leads to coupling matrix elements in a basis which includes electron spin. Nuclear spin is also included by a simple extension of the basis set. It is then argued that many open-shell collisions leading to rotational energy transfer will be sufficiently weak that the coupled equations can be treated by use of the restricted distorted-wave Born approximation. This method leads to the derivation of expressions for scattering cross-sections in both the spin-independent and spin-correlated cases. The influence of exchange forces is manifest in branching fractions for spin multiplets, which relate the cross-sections for the different ΔJassociated with each change in rotational quantum numbers. A general expression for the branching fractions in hyperfine multiplets is also derived. The discussion deals with the extent to which exchange forces will influence rotational energy transfer in practice. It shows how the results of experimental investigations such as those in the following paper might be interpreted. The way in which rotational propensity rules may be affected by exchange interactions is illustrated by reference to the model systems H + CN and H + NH2. In conclusion it is noted that open-shell open-shell collisions take place naturally both in the upper atmosphere and in interstellar space.

Line broadenings within the alkali metal hyperfine multiplets of ion pairs and triple ions. A theoretical approach

The effect of rotational diffusion on the metal hyperfine multiplets in the e.s.r. spectra of ion pairs and cationic ion triplets of alkali metal cations and aromatic radical anions is investigated theoretically. The triple ion of lithium and pyrazine is chosen as a model system; the broadening parameters are calculated for various structures of the triple ion. The results indicate that the anisotropic lithium hyperfine dipolar couplings, being modulated simultaneously with the anisotropic g-tensor, produce high-field broadening of the lithium septet, irrespective of the positions of the cations. Furthermore, it is concluded that there is no triple ion structure for which all the lithium broadening parameters vanish. Finally it is found that the calculated parameters are very small. In general, the anisotropy of the alkali hyperfine coupling in ion pairs and triple ions will be insufficient to account for the linewidth variations observed in these systems.

Pressure broadening of the NO 2 hyperfine multiplet at 93 GHz

Line shapes of the hyperfine NO 2 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δ F=δ J=δ N=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10 -5 cm -1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10 -4 cm -1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ⋍10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line.

The interpretation of linewidth effects in the electron spin resonance spectra of triple ions

The Linewidth trends observed within the alkali metal hyperfine multiplets of electron spin resonance spectra of triple ions are reexamined in terms of two postulated interpretations. The role of cross terms in deciding between these interpretations is emphasized.

ChemInform Abstract: ELECTRON SPIN RESONANCE STUDIES ON BIS(DIMETHYLGLYOXIMATO)COBALT(II) AND ITS COMPLEXES WITH PYRIDINE

The e.s.r. spectra of bis(dimethylglyoximato)cobalt(II) and its pyridine complexes have been studied in methanol. The spectra obtained in both liquid and frozen methanol show the existence of three paramagnetic centres, viz, [Co(Hdmg)2], [Co(Hdmg)2(py)], and [Co(Hdmg)2(py)2](Hdmg is the monoanion of dimethylglyoxime), and that of a diamagnetic adduct [{Co(Hdmg)2(py)}2]. The magnetic parameters have been determined for each paramagnetic species; a significant temperature dependence has been observed in the case of [Co(Hdmg)2]. The parameters indicate a low-spin 2A1 ground state. The Fermi-contact term for [Co(Hdmg)2] varies between –20.0 × 10–4 and –10.5 × 104 cm–1 on decreasing the temperature from 62 °C to the freezing point of methanol; the values for [Co(Hdmg)2(py)] and [Co(Hdmg)2(py)2] are –3.9 × 10–4 and 9.8 – 10–4 cm–1, respectively, at liquid-nitrogen temperature. The observed trend is consistent with the variation in the axial ligand field, which affects the Fermi term through 3d–4s mixing. The linewidth variation of the hyperfine multiplet in the e.s.r. spectrum of [Co(Hdmg)2] has been studied in methanol as a function of temperature. The widths of the strongly overlapping lines have been determined by an automatic-fitting procedure. Good simulation and rapid convergence have been obtained by assuming Lorentzian lineshapes. The predominant factors contributing to the linewidths are spin-rotational relaxation at high temperatures and anisotropic relaxation at low temperatures.

Linewidth variations of ESR spectra in solid state

A statistical model is proposed to explain the linewidth variation of the hyperfine multiplet in the solid state (powder or glass) ESR spectra for Mn(II)- and VO(II)-polygalacturonate as well as Co(II)-dimethylglyoxime. Considering the local magnetic field and the principal values of tensors in the spin Hamiltonian as random variables, we obtain the following linewidth variation formula: W M=(α+βM+γm 2) 1 2 . The linewidth variation determined by the accurate simulation of ESR spectra is in good agreement with the proposed formula. In all our examples the major contribution to the linewidth is inhomogeneous distribution of the ligand field.

Electron spin resonance studies on bis(dimethylglyoximato)cobalt(II) and its complexes with pyridine

The e.s.r. spectra of bis(dimethylglyoximato)cobalt(II) and its pyridine complexes have been studied in methanol. The spectra obtained in both liquid and frozen methanol show the existence of three paramagnetic centres, viz, [Co(Hdmg)2], [Co(Hdmg)2(py)], and [Co(Hdmg)2(py)2](Hdmg is the monoanion of dimethylglyoxime), and that of a diamagnetic adduct [{Co(Hdmg)2(py)}2]. The magnetic parameters have been determined for each paramagnetic species; a significant temperature dependence has been observed in the case of [Co(Hdmg)2]. The parameters indicate a low-spin 2A1 ground state. The Fermi-contact term for [Co(Hdmg)2] varies between –20.0 × 10–4 and –10.5 × 104 cm–1 on decreasing the temperature from 62 °C to the freezing point of methanol; the values for [Co(Hdmg)2(py)] and [Co(Hdmg)2(py)2] are –3.9 × 10–4 and 9.8 – 10–4 cm–1, respectively, at liquid-nitrogen temperature. The observed trend is consistent with the variation in the axial ligand field, which affects the Fermi term through 3d–4s mixing. The linewidth variation of the hyperfine multiplet in the e.s.r. spectrum of [Co(Hdmg)2] has been studied in methanol as a function of temperature. The widths of the strongly overlapping lines have been determined by an automatic-fitting procedure. Good simulation and rapid convergence have been obtained by assuming Lorentzian lineshapes. The predominant factors contributing to the linewidths are spin-rotational relaxation at high temperatures and anisotropic relaxation at low temperatures.