Multiple-photon ir excitation of electronic states of OsO4 molecule

Basic experimental characteristics of collisionless luminescence of OsO₄ molecule excited by pulsed ir laser radiation are presented. The theoretical model of the process is developed and a comparison with experiment is carried out both for one-frequency and two-frequency ir excitation. From such comparison information is obtained on the fraction of molecules excited by laser radiation as well as on the spectroscopic characteristics of highly excited states.     

The two-frequency nuclear quadrupole resonance for explosives detection

The two-frequency nuclear quadrupole resonance (NQR) of¹⁴N nuclei is described for purposes of explosives detection. Two applications are known: two-frequency NQR for increasing the signal intensity, two-frequency NQR for improved reliability of explosives detection. The two-frequency experiments were carried out in hexahydro-1,3,5-trinitro-s-triazine C₃H₆N₆O₆ and sodium nitrite NaNO₂ as a substitute for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocycine C₄H₈N₈O₈. The two-frequency sequences for NQR are proposed for increasing the amplitude of NQR signal and improvement of detection condition.     

Application of the spherical tensor method for Two-Frequency pure NQR of spinI=1 nuclei

The results of a theoretical investigation of two-frequency excitation in pure nuclear quadrupole resonance (NQR) for a spinI=1 nucleus with a nonaxial elecric field gradient are presented. The multipole tensor operator technique is used for the treatment of the one- and two-frequency pulse excitations. The results are applied to the characterization of the two-frequency signal of nitrogen¹⁴N nuclei. The experiments on sodium nitrite, NaNO₂, confirm the presence of additional (two-frequency) echo in the NQR signal. The effect of resonance offsets on two-frequency NQR is also considered.     

Characteristics of multiple-photon dissociation of OsO4 molecule by two frequency tunable CO2-laser pulses

Using two-frequency technique for the multiple photon dissociation of OsO₄ molecule by IR laser radiation, the following new results have been obtained: 1. the narrow resonances of multiple photon absorption on few low lying vibrational transitions have been found in the dissociation yield as a function of exciting frequency ν₁; 2. the structure of the dissociation yield as a function of dissociating frequency ν₂ connected with high lying vibrational transition has been studied; 3. the kinetic of the vibration relaxation of high vibrationally excited molecules was investigated; 4. the unimolecular character of the multiple photon dissociation of OsO₄ has been proved.     

Li and K NMR relaxation study of a LiKSO4 single crystal

The ⁷Li and ³⁹K NMR relaxations in a LiKSO₄ single crystal grown by the slow evaporation method were investigated by employing a pulse NMR spectrometer. From the experimental data, the quadrupole coupling constant and asymmetry parameter were determined at the temperatures of 180 and 300 K. The relaxation processes of ⁷Li and ³⁹K were studied for the LiKSO₄ crystal, and the relaxation times for the ⁷Li and ³⁹K nuclei exhibit remarkable changes near T_c2 (=190 K). The activation energies for ⁷Li and ³⁹K were determined in phases I and III. The large change in the activation energy at 190 K indicates that the Li and K ions are significantly affected during this transition. The correlation time of the ⁷Li calculated from the spin-lattice relaxation time and quadrupole parameters was larger than that of the ³⁹K calculated using the same method. The reason for this is that the Li ion undergoes molecular motion as in the LiO₄ groups.     

Nuclear quadrupole spin-lattice relaxation in Bi4Ge3O12 single crystals doped with atoms of d or f elements. Crystal field effects in compounds exhibiting anomalous magnetic properties

The nuclear quadrupole spin-lattice relaxation was studied in the range 4.2–300 K for single crystals of Bi₄Ge₃O₁₂ doped with minor amounts (the tenth fractions of mol%) of paramagnetic atoms of Cr, Nd, and Gd. Unusual spin dynamic features were recently found for these crystals at room temperature: a dramatic (up to 8-fold) increase in the effective nuclear quadrupole spin-spin relaxation time T ₂* occurred upon doping the pure Bi₄Ge₃O₁₂ sample. Unlike T ₂*, the effective spin-lattice relaxation time T ₁* at room temperature differs insignificantly for both doped and pure samples. But at lower temperatures, the samples exhibit considerably different behavior of the spin-lattice relaxation with temperature, which is caused by different contributions to the relaxation process of the dopant paramagnetic atoms. The distinctive maximum in the temperature dependence of the spin-lattice relaxation time for the Nd-doped crystal is shown to result from the crystal electric field effects.     

Two-frequency effects in nuclear quadrupole resonance

A number of new effects which occur in the two-frequency excitation of a multilevel spin-system in nuclear quadrupole resonance are described. Three programs for observing the effect of trapping, used to detect some transitions in a multilevel system in terms of others, for an accurate determination of the asymmetry parameter of the gradient of the electric field, to identify lines of the multiplet spectrum of nuclear quadrupole resonance, and to investigate the phenomenon of cross-relaxation, are proposed. Quantitative estimates are given of the value of the trapping when two neighboring transitions are excited. The phenomenon of slow beats between signals of a two-frequency echo and the frequency of the transition ±3/2±5/2 for = 0 when an external magnetic field is applied is explained. The reason for the short spin-spin relaxation times in the secondary echoes is established. The experimental method and a block diagram of a two-frequency nuclear quadrupole resonance system are described.This paper was presented at an All-Union Symposium on Magnetic Relaxation in June 1971 in Leipzig.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 82–88, March, 1973.In conclusion we wish to thank V. A. Shishkin, M. Z. Yusupov, and A. D. Gordeev, for their help and for useful discussions.     

Polaronic and charge ordering effects in Pr 0.5 Sr 0.5 Mn 1− x Fe x O 3

In this work we report the results of X-ray diffraction and Mössbauer spectroscopy for the systems Pr_0.5Sr_0.5Mn_1???x Fe _x O₃ (with x?=?0.05, 0.10, 0.15, 0.20, 0.25, 0.30). XRD patterns indicated that all samples were single phase with slightly distorted orthorhombic symmetry. Room temperature Mössbauer spectra are all quadrupole split, indicating paramagnetic relaxation of the Fe moment for all values of Fe concentrations. The spectra are fitted with two doublet components associated with Fe^3?+? ions in octahedral sites with different distortions. Mössbauer spectra recorded at liquid nitrogen temperature for this system also indicate paramagnetic relaxation of the Fe moments down to liquid nitrogen temperature (LNT). In these spectra a third quadrupole component with quadrupole splitting close to zero develops. This component is associated with the delocalization of the charge carriers and the consequent disappearance of lattice distortions produced by the polaronic effect at room temperature. The component with the high quadrupole splitting (0.81 to 1.07 mm/s) results from Jahn–Teller distortion as a consequence of charge ordering transition at low temperature.     

35Cl N.M.R. relaxation in aqueous sodium perchlorate solutions

The relaxation time, T _1ρ, for ³⁵Cl in perchlorate ion in aqueous solutions is found to be 0·25 s. T _1ρ is insensitive to the presence of most first row transition metals; however, a weak complex with manganous ion is demonstrated, and the perchlorate ion-manganous exchange rate is shown to be between 3 × 10⁴ s^-1 and 3·6 × 10⁷ s^-1. In the absence of manganous ion, the relaxation is dominated by the nuclear electric quadrupole interaction; however, a dipolar contribution is observed with manganous ion present.     

Mössbauer spectroscopy of laser annealed tellurium implanted silicon (II).129I

Laser annealed^129mTc-implanted silicon has been investigated using¹²⁹I Mössbauer spectroscopy. At least three dopedependent charge states of substitutional iodine are found. For heavily doped p-type Si a single line component S₁, with isomer shift S=0.96(4) mm/s w. r. t. Cu¹²⁹I and an effective Debye temperature ?′=196(3) K is observed. This component is attributed to I⁺⁺. For compensated Si a single line component, S₂, assigned to I⁺, with S=2.39 (4) mm/s and ?′=170 (3) K is found. For n-type Si, a component S₃, characterized at 4.2 K by S=2.15 (4) mm/s and a quadrupole splitting eQV_zz/h=452 (8) MHz (n?0)is observed. At higher temperatures S₃ shows quadrupole relaxation and its recoilless fraction becomes strongly anisotropic. This behaviour is explained on the basis of a transition from a static to a dynamic Jahn-Teller distortion. Component S₃ has been attributed to I⁰. In the spectra of compensated and n-type Si a less well-defined component Q, with parameters resembling those of S₃ but showing no quadrupole relaxation, is observed. This component has tentatively also been assigned to I^o. The results can be understood qualitatively on the basis of a simple MO-model.     

Effect of <Superscript>14</Superscript>N Nucleus Capture in Nuclear Quadrupole Resonance at Small Relaxation Parameters

Experiments on detecting induction signals of nuclear quadrupole resonance (NQR) on ¹⁴N nuclei in hexahydro-1,3,5-trinitro-s-triazine C₃H₆N₆O₆ (RDX) with preliminary changed population densities of NQR energy levels upon exposure to a saturating pulse are described. It is demonstrated that this actually causes the induction signal amplitude to change; however, complete saturation of the transition cannot be reached because of the NQR relaxation time. It is also demonstrated that the results of calculations without regard for the relaxation processes in RDX lack experimental support. Experimental data demonstrate the feasibility of application of the methods of preliminary change of the population densities (by pumping) for multifrequency experiments in NQR and explosive detection.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 49–52, April, 2005.     

Quadrupole spin-echo envelopes for Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> single crystals doped with the atoms of transition and rare-earth elements

The influence of a weak (below 50 Oe) constant magnetic field on a quadrupole spin-echo envelope was studied for an undoped single crystal Bi₄Ge₃O₁₂, in which local magnetic fields on the order of 20–30 G were previously found, as well as for single Bi₄Ge₃O₁₂ crystals doped with the atoms of transition and rare-earth elements. In all of these cases, the spin-echo envelopes were strongly influenced. A considerable increase in the nuclear spin-spin relaxation time T ₂ was observed for the undoped sample upon the switching of weak external magnetic fields. For the doped samples, the spin-echo envelope decay became much slower already in the zero field. The external magnetic fields exhibited a markedly weaker influence on the spin-echo envelope for the doped samples. The text was submitted by the authors in English.     

Electric field gradients at Zr sites and phase transition in the Nasicon-type compound Na5Zr(PO4)3

The quadrupole coupling parameters of the ¹⁸¹Ta probe placed in substitution for zirconium were measured by Perturbed Angular Correlation (PAC) Spectroscopy in a polycrystalline sample of the Na₅Zr(PO₄)₃ composition between R · T and 400°C. The PAC spectra indicate the existence of a transition which spreads out over a rather large temperature range between 90 and 130°C. The results are coherent with the X-ray diffraction data previously reported on this compound. Spin relaxation phenomena are observed, which give evidence that the phase transition induces important modifications on the local motions of Na⁺-ions.     

A relaxation times coupling method to construct acoustic relaxation calibration for two-frequency measuring gas compositions

In our previous work (Hu et al., 2014), a method has been proposed to detect gas compositions by locating the acoustic spectral peaks, which can be detected only by two-frequency acoustic measurements in practice. However, as a ‘Detection Calibration’, the effective relaxation area (ERA) constructed by existing theoretical model cannot match the two-frequency measurements when there are more than one strong relaxational components in gas mixtures. This paper proposes a method to construct the ERA by coupling the decoupled single relaxation times together to a whole relaxation time. For gas mixtures with only one single relaxation process, the predicted ERA results match with the experimental data better than those predicted by the existing model. Moreover, for gas mixtures in which more than one relaxation process are significant, the ERA results predicted by the proposed method also match with the detection results of two-frequency measurements better than the existing model. This relaxation time coupling based ERA constructing method is validated by the application in low-quality natural gas detection.     

Nuclear magnetic resonance study of Na (DxH1−x)3(SeO3)2 crystals

A comparison of the quadrupole perturbed deuteron magnetic resonance spectra of the α,β, and γ phase of partially deuterated sodium trihydrogen selenite crystals shows that not only in the monoclinic γ but also in the triclinic β phase the deutrons are ordered whereas they are disordered in the α phase. Spin-lattice relaxation time measurements show the existence of slow hindered rotations of the HSeO₃ and H₂SeO₃ groups at high temperatures as well as the existence of an overdamped ferroelectric soft mode which condenses at the paraelectric to ferroelectric transition.     

类铍离子磁四极M2 2s2 1S0—2s2p3P2 (Z=10—103)禁戒跃迁

利用全相对论多组态Dirac-Fock方法系统地计算了高离化类铍离子的磁四极M2 2s²¹S₀—2s2p³P₂ (Z=10—103)自旋禁戒跃迁的能级间隔、跃迁概率和振子强度，计算中考虑了重要核的有限体积效应，Breit修正和QED修正，所得结果和最近的实验数据以及理论值进行了比较，结果表明：高原子序数的高电荷离子(Z≥70)磁四极M2自旋禁戒跃迁几乎可以和中性原子的光学允许跃迁相比拟，不仅在天体等离子体中，在ICF和MCF高温激光等离子体中，磁四极自旋禁戒跃迁和其他自旋禁戒跃迁（磁偶极、电四极）一样不容忽视，在双电子复合、不透明度、自由程等理论计算中应该考虑其影响. 关键词： 磁四极M2 能级间隔 跃迁概率 振子强度     

Al nuclear magnetic resonance study of synthetic and natural corundum (α-Al2O3) Some experimental aspects of quantitative Al nuclear magnetic resonance spectroscopy

The ²⁷Al nuclear magnetic resonance (NMR) response of a series of natural and synthetic corundum (α-Al₂O₃) samples is studied quantitatively by short-pulse excitation and frequency-stepped adiabatic half-passage (FSAHP). Using on- and off-resonance nutation NMR, it was established that the quadrupole coupling parameters of visible Al is identical in all samples. Remarkably, the relaxation behavior for the aluminum is very different in the various samples and has a marked effect on the quantitative response. In natural corundum samples the ²⁷Al spin-lattice relaxation is very efficient as these samples contain paramagnetic impurities. As a result, however, the full signal could not be recovered, which is attributed to relaxation broadening of spins in the vicinity of these impurities. In synthetic samples, containing no impurities, the full signal could be recovered, although the relaxation behaviour appeared to depend strongly on the preparation method. We observed differences in the spin-lattice relaxation by a factor 20; the longest T₁ was observed in a crushed single crystal. This implies that α-Al₂O₃ can only be used as a standard in quantitative analyses if it has been characterized thoroughly. Furthermore, the effective relaxation behaviour for different types of excitation is studied. Finally, a method to measure the spin-lattice relaxation of half-integer quadrupole nuclei is introduced, using a frequency-stepped adiabatic passage (FSAP) to invert the spin system.     

The effect of quadrupole relaxation on nuclear magnetic resonance multiplets

A theory of the broadening of multiplet components in magnetic resonance spectra of coupled nuclei due to electric quadrupole spin-lattice relaxation is presented. It is shown that the broadening of the components of the 1:1:1 triplet for nuclei of spin 1/2 coupled to a nucleus of spin 1, is 3/2 as great for the outer lines as for the central one, provided that the rate of quadrupole relaxation is not too large. This is in agreement with experimental observations on ¹⁴NH₃. A theory of the line shape of the partly collapsed multiplet at higher rates of quadrupole relaxation is also given.     

Anomalous magnetism and 209Bi nuclear spin relaxation in Bi4Ge3O12 crystals

The quadrupole ²⁰⁹Bi spin–spin and spin–lattice relaxation were studied within 4.2–300 K for pure and doped Bi₄Ge₃O₁₂ single crystals which exhibit, as was previously found, anomalous magnetic properties. The results revealed an unexpectedly strong influence of minor amounts of paramagnetic dopants (0.015–0.5 mol.%) on the relaxation processes. Various mechanisms (quadrupole, crystal electric field, electron spin fluctuations) govern the spin–lattice relaxation time T ₁ in pure and doped samples. Unlike T ₁, the spin–spin relaxation time T ₂ for pure and Nd-doped samples was weakly dependent on temperature within 4.2–300 K. Doping Bi₄Ge₃O₁₂ with paramagnetic atoms strongly elongated T ₂. The elongation, although not so strong, was also observed for pure and doped crystals under the influence of weak (～30 Oe) external magnetic fields. To confirm the conclusion about strong influence of crystal field effects on the temperature dependence of T ₁ in the temperature range 4.2–77 K, the magnetization vs. temperature and magnetic field was measured for Nd- and Gd-doped Bi₄Ge₃O₁₂ crystals using a SQUID magnetometer. The temperature behavior of magnetic susceptibility for the Nd-doped crystal was consistent with the presence of the crystal electric field effects. For the Gd-doped crystal, the Brillouin formula perfectly fitted the curve of magnetization vs. magnetic field, which pointed to the absence of the crystal electric field contribution into the spin–lattice relaxation process in this sample.     

Spin relaxation of quadrupole nuclei in paramagnetic and magnetically ordered insulators

The longitudinal and transverse spin relaxation through a (generally anisotropic) electron-nucleus interaction in paramagnetic and magnetically ordered insulators is theoretically studied for nuclei with a resolved quadrupole structure. Expressions are derived for the relaxation rates of both the transverse nuclear magnetization components when individual transitions are excited in the quadrupole structure and the total longitudinal nuclear magnetization component. These expressions are reduced to a form that contains the Fourier transforms of the time correlation functions only for the electron spins. Given the specific form of these correlation functions corresponding to different phase states of the electron spins and different origins of their fluctuations, the temperature dependences of the nuclear relaxation rates are ascertained in various cases, including those for dipole and isotropic hyperfine interactions. Calculations are performed for arbitrary electron and half-integer nuclear spins by taking into account the possible quadrupole splitting of the NMR spectrum without any restriction on the smallness of the ratio ?ω s/k_BT (ω_s is the resonance frequency of the electron spins). The derived expressions are compared with available experimental data on the longitudinal and transverse nuclear relaxation in colossal-magnetoresistance lanthanum manganites in the part of their phase diagram where the corresponding samples are either paramagnetic or magnetically ordered insulators and near the points of transition to an ordered state. Interpretations alternative to the existing ones are offered.