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1.
Solid State Nucl Magn Reson ; 93: 7-15, 2018 09.
Article in English | MEDLINE | ID: mdl-29803916

ABSTRACT

We studied deuteron NMR spectra and spin-lattice relaxation of deuterated acetone-d6, adsorbed into zeolites NaX (1.3) and NaY(2.4) at 100% coverage of sodium cations. At temperatures roughly below 160 K the deuterons are localized and their NMR characteristics are determined by CD3 rotation and rotational oscillations of acetone molecules. In NaX the CD3 rotation and rotational oscillations about the twofold axis of acetone dominate the spectra below 100 K, while above it oscillations also about other axes become important. In NaY dominant features are related to methyl tunnelling and to a smaller extent to rigid acetones, before the rotational oscillations about twofold axis start to prevail above 40 K. The analysis of the strongly non-exponential magnetization recovery was done by applying the recently introduced method (Ylinen et al., 2015 [12]), improved here to take into account the limited fast recovery at the level crossings, 10% at ωt=ω0 and 28% at ωt=2ω0. At first the experimental recovery is fitted by three exponentials with adjustable weights and decay rates. Then these quantities are calculated from activation energy distributions and known expressions for the deuteron relaxation rate. In NaY two distinctly separate activation energy distributions were needed, the dominant one being very broad. The use of three distributions, two of them covering practically the same energies as the broad one, lead to a somewhat better agreement with experiment. In general the theoretical results agree with experiment within experimental scatter. As the final result the mean activation energies and widths are obtained for activation energy distributions.

2.
J Phys Condens Matter ; 28(30): 305501, 2016 08 03.
Article in English | MEDLINE | ID: mdl-27269809

ABSTRACT

We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green's function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1-c at three representative concentrations c = 0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

3.
Solid State Nucl Magn Reson ; 71: 19-29, 2015 Oct.
Article in English | MEDLINE | ID: mdl-26482130

ABSTRACT

Deuteron NMR spectra and spin-lattice relaxation were studied experimentally in zeolite NaY(2.4) samples containing 100% or 200% of CD3OH or CD3OD molecules of the total coverage of Na atoms in the temperature range 20-150K. The activation energies describing the methyl and hydroxyl motions show broad distributions. The relaxation data were interpreted by improving a recent model (Stoch et al., 2013 [16]) in which the nonexponential relaxation curves are at first described by a sum of three exponentials with adjustable relaxation rates and weights. Then a broad distribution of activation energies (the mean activation energy A0 and the width σ) was assumed for each essentially different methyl and hydroxyl position. The correlation times were calculated from the Arrhenius equation (containing the pre-exponential factor τ0), individual relaxation rates computed and classified into three classes, and finally initial relaxation rates and weights for each class formed. These were compared with experimental data, motional parameters changed slightly and new improved rates and weights for each class calculated, etc. This method was improved by deriving for the deuterons of the A and E species methyl groups relaxation rates, which depend explicitly on the tunnel frequency ωt. The temperature dependence of ωt and of the low-temperature correlation time were obtained by using the solutions of the Mathieu equation for a threefold potential. These dependencies were included in the simulations and as the result sets of A0, σ and τ0 obtained, which describe the methyl and hydroxyl motions in different positions in zeolite.

4.
J Phys Condens Matter ; 25(49): 495501, 2013 Dec 11.
Article in English | MEDLINE | ID: mdl-24184730

ABSTRACT

We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.

5.
Solid State Nucl Magn Reson ; 49-50: 33-41, 2013 Feb.
Article in English | MEDLINE | ID: mdl-23245836

ABSTRACT

A new method is introduced for analyzing deuteron spin-lattice relaxation in molecular systems with a broad distribution of activation energies and correlation times. In such samples the magnetization recovery is strongly non-exponential but can be fitted quite accurately by three exponentials. The considered system may consist of molecular groups with different mobility. For each group a Gaussian distribution of the activation energy is introduced. By assuming for every subsystem three parameters: the mean activation energy E(0), the distribution width σ and the pre-exponential factor τ(0) for the Arrhenius equation defining the correlation time, the relaxation rate is calculated for every part of the distribution. Experiment-based limiting values allow the grouping of the rates into three classes. For each class the relaxation rate and weight is calculated and compared with experiment. The parameters E(0), σ and τ(0) are determined iteratively by repeating the whole cycle many times. The temperature dependence of the deuteron relaxation was observed in three samples containing CD(3)OH (200% and 100% loading) and CD(3)OD (200%) in NaX zeolite and analyzed by the described method between 20K and 170K. The obtained parameters, equal for all the three samples, characterize the methyl and hydroxyl mobilities of the methanol molecules at two different locations.

6.
Solid State Nucl Magn Reson ; 45-46: 66-74, 2012.
Article in English | MEDLINE | ID: mdl-22819978

ABSTRACT

Nuclear magnetic resonance (NMR) provides means to investigate molecular dynamics at every state of matter. Features characteristic for the gas phase, liquid-like layers and immobilized methanol-d(4) molecules in NaX and NaY zeolites were observed in the temperature range from 300 K down to 20K. The NMR spectra at low temperature are consistent with the model in which molecules are bonded at two positions: horizontal (methanol oxygen bonded to sodium cation) and vertical (hydrogen bonding of hydroxyl deuteron to zeolite framework oxygen). Narrow lines were observed at high temperature indicating an isotropic reorientation of a fraction of molecules. Deuteron spin-lattice relaxation gives evidence for the formation of trimers, based on observation of different relaxation rates for methyl and hydroxyl deuterons undergoing isotropic reorientation. Internal rotation of methyl groups and fixed positions of hydrogen bonded hydroxyl deuterons in methyl trimers provide relaxation rates observed experimentally. A change in the slope of the temperature dependence of both relaxation rates indicates a transition from the relaxation dominated by translational motion to prevailing contribution of reorientation. Trimers undergoing isotropic reorientation disintegrate and separate molecules become localized on adsorption centers at 166.7 K and 153.8K for NaX and NaY, respectively, as indicated by extreme broadening of deuteron NMR spectra. Molecules at vertical position remain localized up to high temperatures. That indicates the dominating role of the hydrogen bonding. Mobility of single molecules was observed for lower loading (86 molecules/uc) in NaX. A direct transition from translation to localization was observed at 190 K.

7.
J Phys Condens Matter ; 23(26): 265004, 2011 Jul 06.
Article in English | MEDLINE | ID: mdl-21642750

ABSTRACT

The surface properties of Fe-rich ferromagnetic Fe-Cr alloys are investigated using a first-principles quantum-mechanical method. In dilute alloys, the surfaces are dominated by Fe, whereas the Cr-containing surfaces become favorable when the bulk Cr concentration exceeds the limit of ∼ 10 atomic per cent. The abrupt change in the surface behavior is the consequence of complex competing magneto-chemical interactions between the alloying atoms. Considering the quantities of various features: equilibrium surface profiles, chemical potentials, segregation energies, surface energies, magnetic moments, mixing energies and pair interactions, within a wider range of bulk and surface concentrations enables us to build a comprehensive picture of the physics of Fe-Cr surfaces. Using the present achievements many previously controversial results can now be merged into a consistent model of Fe-rich Fe-Cr alloys.

8.
Phys Rev Lett ; 106(5): 057202, 2011 Feb 04.
Article in English | MEDLINE | ID: mdl-21405426

ABSTRACT

Because of the increased electron density within the surface layer, metal surfaces are generally expected to have tensile surface stress. Here, using first-principles density functional calculations, we demonstrate that in magnetic 3d metals surface magnetism can alter this commonly accepted picture. We find that the thermodynamically stable surfaces of chromium and manganese possess compressive surface stress. The revealed negative surface stress is shown to be ascribed to the enhanced magnetic moments within the surface layer relative to the bulk values.

9.
Solid State Nucl Magn Reson ; 37(3-4): 91-100, 2010.
Article in English | MEDLINE | ID: mdl-20561770

ABSTRACT

Deuteron spin-lattice relaxation and spectra were measured for NaDY (0.8) zeolite containing some heavy water. Two subsystems of deuterons with different mobility were disclosed at low temperatures with their respective relaxation rates differing by two orders of magnitude. Spectra exhibit different shapes related directly to a specific motional model. Hydroxyl deuterons perform incoherent tunneling along the hydrogen bond, then on increasing temperature jumps to excited states and over the barrier appear. Hydrogen bonded water molecules perform 180 degrees rotational jumps about the twofold symmetry axis. Spectral amplitudes are consistent with the water content of 13 D(2)O molecules per unit cell. Above about 240K translational mobility becomes significant and finally water molecules diffuse across the free space of cages. Diversity in temperature dependence of hydroxyl deuteron dynamics may indicate location of adsorbed molecules.

10.
Solid State Nucl Magn Reson ; 35(3): 180-6, 2009 Jun.
Article in English | MEDLINE | ID: mdl-19272759

ABSTRACT

Deuteron NMR spectra and relaxation were studied at the resonance frequency of 46MHz in polycrystalline fully and partly deuterated (NH(4))(2)ZnCl(4) between 300 and 5K. Spectral components confirm existence of ammonium positions with different potential symmetry, resulting in two- and threefold reorientation of ammonium ions. The temperature dependence of the spin-lattice relaxation rate discloses two time constants in the whole range. The fitting procedure allows the separation into contributions from subsystems of ions in respective potentials. Two relaxation rate maxima are attributed to ions performing threefold uniaxial reorientation at low temperatures. The lower-temperature maximum is observed at T36K. With increasing temperature reorientations about remaining axes start to contribute leading to the other maximum near 100K. The other category of ammonium ions gives rise to the maximum at about 50K. Below this temperature the dominant motion seems to be 180( composite function) reorientations about one twofold axis according to observed spectra. Consistent picture of ion mobility is accomplished for 5%, 30%, 70% and 100% deuterated compounds.

11.
Solid State Nucl Magn Reson ; 35(3): 172-9, 2009 Jun.
Article in English | MEDLINE | ID: mdl-18693087

ABSTRACT

Deuteron spin-lattice relaxation via the motion-dependent part of the electric quadrupole interaction is discussed in partly and fully deuterated ammonium ions of ammonium hexachlorometallates. The dominant motion at temperatures T>50K is normally 120 degrees reorientations of the ammonium ions. In some hexachlorometallates the instantaneous equilibrium directions of the nitrogen-hydrogen vectors make a certain angle Delta with the metal-nitrogen vectors and they appear in groups of six near each metal-hydrogen vector. Each N-D vector jumps between the six directions of one group and this motion (called limited jumps) dominates the deuteron relaxation at lower temperatures. In some samples one direction of each group seems to become more populated than the others when the deuteration degree exceeds a certain value and the ammonium ions become ordered. A model is derived for the relaxation rate in the absence of tunnelling splittings, which includes the effects of reorientations and limited jumps also in the ordered structure, where the limited-jump rate of a N-D vector to the preferred direction, r(p), differs from that to the nonpreferred direction, r(n). The obtained relaxation rate depends, in addition to the angle Delta, also on the ratio d=r(n)/r(p). The effect of d is discussed and estimates for it are presented on the basis of earlier experiments. The recent model for the deuteron relaxation in NH(3)D(+) ions, including the effect of proton tunnelling, is shortly reviewed. At lowest temperatures the motional rates can be dominated by corresponding incoherent tunnelling and the rate of the incoherent tunnelling contributing to limited jumps is argued to be clearly larger than that of the incoherent tunnelling contributing to approximately 120 degrees rotations.

12.
Solid State Nucl Magn Reson ; 34(1-2): 77-85, 2008.
Article in English | MEDLINE | ID: mdl-18585902

ABSTRACT

Deuteron spin-lattice relaxation and spectra were studied in partially and fully deuterated (NH(4))(2)PdCl(6) in the temperature range 5-300K. The relaxation rate maximum was observed at 45K in (ND(4))(2)PdCl(6). Its value is reduced due to limited jumps by about 33% relative to the theoretical value expected for threefold reorientations. Limited jumps correspond to an N-D vector jumping between six directions on a cone around a Pd-N vector, the angle between the N-D and Pd-N vectors being denoted Delta. This motion makes a part of the quadrupole interaction ineffective in relaxation thus reducing the maximum rate at 45K. The observed reduction leads to the value Delta=21( composite function). Limited jumps are quenched to a large extent at the order-disorder phase transition and consequently a decrease is observed in the rate. Below the transition ND(4)(+) ions reorient between the tetrahedral orientations of the ordered phase, therefore the quadrupole interaction has the full relaxing efficiency. In the 10% deuterated sample the temperature of the rate maximum is shifted to 35K and below 20K the rate itself is one order of magnitude larger than in (ND(4))(2)PdCl(6). The increase is related to (1) the absence of the order-disorder phase transition and (2) to the enhanced mobility of NH(3)D(+) because of its electric dipole moment. Limited jumps are claimed to be the dominant relaxation mechanism below 20K. The relaxation in the disordered 30% deuterated sample is quite similar to that in 10% sample. The 50% and 70% deuterated samples undergo a transition to the ordered phase. The relaxation is biexponential with the characteristic rates somewhat smaller than those in (ND(4))(2)PdCl(6), but approaching them with increasing deuteration. This variation can be explained with different mobilities and varying relative numbers of the various isotopomers NH(4-n)D(n)(+), n=1-4.

13.
J Chem Phys ; 128(18): 184510, 2008 May 14.
Article in English | MEDLINE | ID: mdl-18532829

ABSTRACT

Deuteron NMR relaxation and spectra were studied at the resonance frequency of 46 MHz in polycrystalline (ND(4))(2)PtCl(6) between 300-5 K. The relaxation rate maximum near 50 K is about 53% smaller than the calculated maximum related to 120 degrees rotations about the threefold symmetry axes of the ammonium ion. The difference is explained by assuming for a N-D vector a total of 24 equilibrium directions, which in groups of six deviate from the nearest Pt-N vector by a certain angle Theta. So-called limited jumps between the directions of each group take place much more frequently than the large-angle rotations, thus rendering a fraction of the deuteron quadrupole coupling ineffective in relaxation. A motional model is presented, which takes into account both these motions simultaneously. A comparison with experimental data leads to Theta=26.0 degrees , in reasonable agreement with earlier neutron diffraction data. A sharp decrease found in the relaxation rate at the order-disorder phase transition temperature of 27.2 K is related to the fact that one of the six equilibrium directions becomes preferred. This leads to a formation of ordered domains, in which the active motion driving the relaxation is 120 degrees rotations. Two components in the spectra found below 55 K are related to domains (broad) and transition regions between domains (narrow). Reasons for the nonexponentiality observed below 20 K are discussed, the most likely explanation being that limited jumps dominate within transition regions and make the corresponding deuterons relax faster than those in domains.

14.
Phys Rev Lett ; 100(8): 086101, 2008 Feb 29.
Article in English | MEDLINE | ID: mdl-18352637

ABSTRACT

First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2x1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2x1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.

15.
J Chem Phys ; 127(20): 204714, 2007 Nov 28.
Article in English | MEDLINE | ID: mdl-18052453

ABSTRACT

Deuteron spin-lattice relaxation was applied to study translational and rotational mobility of CD(4) molecules trapped in the cages of zeolites. Tetrahedral methane molecules are treated as quantum rotators. Relaxation rates related to the intraquadrupole interaction are derived for the T and A+E symmetry species in the presence of large tunneling splittings, consistently with the assumption that A and E species molecules relax at the same rate. An exchange model is presented, which describes the effect on relaxation of CD(4) jumping between two positions characterized by different potentials. While staying at either position bonded to an atom or ion at the cage wall, the molecule has some freedom to move in the vicinity. This causes a time-dependent external electric field gradient, which contributes to the deuteron relaxation rate via the electric quadrupole interaction. Spin conversion transitions couple the relaxation of magnetizations M(T) and M(AE), which is taken into account by reapplying the presented model under somewhat different conditions. Such a two-step procedure leads to successful fits with the experimental results obtained in the range of temperatures roughly 20-200 K for zeolites HY, NaA, and NaMordenite. At higher temperatures CD(4) molecules fly freely across zeolite cages and relaxation changes accordingly, while incoherent tunneling dominates for immobile molecules below 20 K.

16.
Solid State Nucl Magn Reson ; 29(4): 330-44, 2006 Jun.
Article in English | MEDLINE | ID: mdl-16361090

ABSTRACT

Spin diffusion between 13CH3 groups in solids is studied both theoretically and experimentally. It is shown to be dominated by mutual spin flip-flops of protons belonging to neighbouring methyl groups. Also nonmethyl protons may contribute significantly if present in the sample. The spin-rotational ground state of 13CH3 consists of 16 sublevels. When their populations are used to describe spin diffusion, eight population combinations are shown to be important, two of them corresponding to the 13C-proton and proton-proton intra-methyl magnetic dipolar energies, Dc and Dp, respectively. Spin-diffusion transitions modulate these combinations so that a further reduction to two sets of four combinations is possible, with no coupling between the sets. Coupled differential equations are derived to describe the time dependence of the combinations in each set. They are solved numerically and compared with experimental results on a single crystal of aspirin with 13C-labelled methyl groups at the carbon resonance. The 13C NMR induction signal was observed as a function of time after the preparation either at the carbon resonance (a two-pulse sequence) or at the proton resonance (proton saturation). Usually carbon spectra were computed first and then three of the mentioned population combinations were obtained from the individual spectral components. Some results on the time dependence of Dc were also obtained directly from the amplitude of the out-of-phase induction signal. Theoretical predictions are found to describe semiquantitatively the overall time dependence of these three combinations and especially their variation with different initial conditions, which are discussed in detail. Also the partial transfer of the magnetic dipolar energy between Dc and Dp is nicely explained. Reasons for discrepancies are discussed.


Subject(s)
Carbon Compounds, Inorganic/analysis , Carbon Compounds, Inorganic/chemistry , Hydrogen/analysis , Hydrogen/chemistry , Magnetic Resonance Spectroscopy/methods , Models, Chemical , Models, Molecular , Algorithms , Carbon Isotopes/analysis , Carbon Isotopes/chemistry , Computer Simulation , Energy Transfer , Spin Labels
17.
Solid State Nucl Magn Reson ; 23(4): 224-42, 2003 Jun.
Article in English | MEDLINE | ID: mdl-12787905

ABSTRACT

We studied the spin-lattice relaxation of the 13C magnetisation, M(C), in 13C-enriched single crystal of aspirin (only methyl carbons enriched to 99%) at the carbon resonance frequency of 54.5 MHz. After the carbon saturation the recovery appears exponential except below 30K, where it is biexponential due to the presence of the level crossing omega(t)=omega(C)+omega(H) (the symbols refer, respectively, to the tunnel frequency and the carbon and proton resonance frequencies in angular units). After the saturation of the proton magnetisation, M(H), the description of the M(C) recovery needs three exponentials. The evaluation of the time constants is easiest from the data in this case, since M(C) varies with time in an initial growth-subsequent decrease (or an initial decrease-subsequent growth depending on temperature) manner, instead of the monotonous growth after the carbon saturation. Experimental data agree semiquantitatively with the predictions of our recent model. According to the model the relaxation of M(C) is coupled to M(H) and the tunnel energy TE at temperatures below the minimum of the 13C relaxation time. Sufficiently above this minimum M(C) is coupled to M(H) and the rotational polarization (but not to TE) in agreement with experiment. Also the effect of torsional oscillations of a methyl group on the magnitude of various 13C-related transition rates was considered in detail. In aspirin the rates are reduced roughly by 10% and the reduction should become larger in samples with a larger tunnel splitting. The reduction also changes somewhat the angular dependence of these rates.


Subject(s)
Aspirin/chemistry , Magnetic Resonance Spectroscopy/methods , Models, Molecular , Carbon/chemistry , Carbon Isotopes , Computer Simulation , Hydrogen/chemistry , Protons , Sensitivity and Specificity , Spin Labels
18.
Solid State Nucl Magn Reson ; 22(2-3): 373-93, 2002.
Article in English | MEDLINE | ID: mdl-12469821

ABSTRACT

A detailed description of the diverse mobility of the ND4+ ions in the low-temperature ordered phase of (ND4)2PtCl4 is developed on the basis of single-crystal deuteron NMR spectra and site-selective T1 measurements. The ordered phase of (ND4)2PtCl4 consists of two kinds of domains in which the orientation of the ND4+ tetrahedra differs by a 90 degrees rotation about an axis which otherwise is a two-fold symmetry axis of the tetrahedra. Inside the domains, the ND4+ ions do not reorient at low temperatures. The domains are separated by domain walls which contain, according to the deuteron NMR spectra, about 10% of all ND4+ ions. These ions are highly mobile even at 10 K. On rising the temperature, the thickness of the domain walls increases, that is, the ions in more and more layers become mobile. Moreover, we provide evidence for fluctuations of the locations of the domain walls. The central resonance of the domain-wall ions shows a complicated structure below 36 K. On the basis of a tunnelling hypothesis we make an attempt to account for this structure. There are indications that the tunnelling process is incoherent.


Subject(s)
Chlorides/chemistry , Computer Simulation , Magnetic Resonance Spectroscopy , Models, Theoretical , Platinum Compounds/chemistry , Quaternary Ammonium Compounds/chemistry , Deuterium , Ions , Models, Molecular , Molecular Conformation , Sensitivity and Specificity , Temperature
19.
Solid State Nucl Magn Reson ; 19(1-2): 19-28, 2001.
Article in English | MEDLINE | ID: mdl-11407600

ABSTRACT

Proton spin-lattice relaxation in a single crystal of (NH4)2S2O8 was studied as a function of resonance frequency at various constant temperatures between 4.2 and 30 K. Two T1 minima were found, one at 8.6 MHz and the other at 4.3 MHz. They are related to the splitting between the lowest T level and the A level, equal to 8.6 MHz nearly independently of temperature below 25 K. Together with the large tunnel splitting of 269 MHz, determined earlier by Clough et al. (Chem. Phys. 152, 343 (1991)) our results define the spin-rotational wavefunction of the lowest T level very accurately, although those of the two higher T levels remain largely undetermined.


Subject(s)
Ammonium Sulfate/chemistry , Magnetic Resonance Spectroscopy/methods , Crystallization , Molecular Structure
20.
J Magn Reson ; 145(2): 326-33, 2000 Aug.
Article in English | MEDLINE | ID: mdl-10910702

ABSTRACT

Double quantum (DQ) filtering is shown to lead to an effective separation of the NMR signals from the para (I = 1) and ortho (I = 2) molecules in solid deuterium. The separation is achieved by the pulse sequence 90(φ)( degrees )-t(pr)-90(φ)( degrees )-t(ev)-90(x)( degrees )-t, where the phase-cycled first two pulses create the DQ coherence. Two components are observed after the third pulse; the para signal shows the maximum at a short time t while the ortho signal reaches the maximum at a longer t. The observed signal can be expressed as (1/2) summation operator(I) [F(I)(t(pr) - t) - F(I)(t(pr) + t)], where F(I)(t) is a proper fitting function for the free induction signal of the para and ortho molecules (with I = 1 or 2, respectively). Numerical fits to experimental data at 4.2 and 2 K show that this method can be used to determine the ratio F(1)(0)/F(2)(0) and thus, because the initial value F(I)(0) is proportional to the respective magnetization before the pulse sequence, the ortho and para concentrations in solid deuterium. Copyright 2000 Academic Press.

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