Deuteron Magnetic Resonance Spectra Research Articles

Probing theYD3structure by2HNMR electric-field gradients: A comparison with first-principles calculations

Electric-field gradients (EFG's) in yttrium trideuteride $({\mathrm{YD}}_{2.98})$ have been determined using deuteron magnetic resonance (DMR) and compared with values for the $P3\ifmmode\bar\else\textasciimacron\fi{}c1$ and ${P6}_{3}\mathrm{cm}$ structures calculated from first principles. The experimental DMR spectra at low temperatures (180--290 K) could be decomposed into two components with intensity ratio $2:1$ in accordance with the expected two groups of deuterium sites, i.e., tetrahedral and octahedral sites in the crystal lattice. Their characteristic quadrupole frequencies, ${\ensuremath{\nu}}_{q},$ and asymmetry parameters, \ensuremath{\eta}, have been compared with the theoretical values obtained for the structures with space groups $P3\ifmmode\bar\else\textasciimacron\fi{}c1$ (no. 165) and ${P6}_{3}\mathrm{cm}$ (no. 185). The agreement between the experimental and calculated results is much better for the latter structure. The spectra at higher temperatures (300--370 K) transform from a two-component configuration into three quadrupolar doublets plus a low-intensity narrow central component. One of the doublets keeps the same parameters as those observed at low temperatures. The two others indicate changes in the tetrahedral site environments. One possible explanation could be a thermally activated quasi-two-dimensional hopping of the D atoms to nearby sites within the $\mathrm{ab}$ plane.

Nuclear magnetic resonance studies of amorphous deuterated silicon nitride thin films

Amorphous hydrogenated/deuterated silicon nitride (a-SiN:H,D) thin films were studied by deuteron magnetic resonance (DMR). DMR spectra show two quadrupolar broadened Pake-type doublets with splittings of 65.4 kHz for SiD, and 154 kHz for ND bonds; the ratio of these DMR doublet cusp-splittings ( Δ ND Δ SiD = 2.35 ) is, to within experimental error, equal to the ratio of the squares of the respective bond-stretching frequencies (( ω ND ω SiD ) 2 = 2.36 ), as determined by analysis of Fourier transform infrared spectra. The center frequencies of the SiD and ND DMR doublets are not coincident, but rather are shifted by ∼ 2 kHz, indicating that the SiD and ND groups are interacting, and must therefore be near-neighbors in the amorphous network. This explanation consistent with an interpretation of the shifts in bond-stretching frequencies of IR modes that occur when Si(H)D and N(H)D modes are found in the same film.

Light-Induced Changes Among Fast-Relaxing Hydrogens in Plasma-Deposited Hydrogenated Amorphous Silicon

ABSTRACTLight-induced rearrangements in a-Si:H,D during and after illumination have been studied by deuteron magnetic resonance (DMR). A film sample was deposited on a 230°C Al substrate by plasma decomposition of S1H4 and D2. The high quality film contained 4 at.% H and 4 at. % D. DMR spectra of fast-relaxing components were examined at 700 msec or less after radio frequency saturation. At 30 K these showed a broad central signal (primarily nanovoid-trapped HD and D2), part of which shifted paramagnetically during illumination. No comparable shifts were shown by spectral components from Si-bonded hydrogen or from microvoid-contained dense fluid hydrogen. The observed post-illumination shifts vanished upon 150°C dark anneal and reflected light-induced metastable magnetic changes in the surroundings of hydrogen trapped in nanovoids.

2H-NMR Study of Orientational Order in Binary Mixtures: A Nematic Phase of Biaxial Molecules

Abstract Deuteron Magnetic Resonance (2H-NMR) spectra have been obtained from a binary mixture of 2-fluorenyl-4′-tetradecyloxy benzoate-d 9 (FLOC14) and para-Xylene-d 10 (p-Xy), as a function of temperature. The liquid crystal, FLOC14, is selectively deuterated on the rigid fluorene moiety while the p-Xy is perdeuterated. The quadrupolar splittings, v k Q allow the unambiguous determination of the temperature dependence of the orientational order parameters, S izz and (S ixx — S iyy), of both species, i = 1,2. These results are the first to provide information on the degree and asymmetry of orientational order, of both biaxial molecules, in the uniaxial nematic phase of a binary mixture. A new approach was adopted for analyzing the experimental data which uses a least squares fit of the quadrupolar spslittings, v k Q, to provide the four component order parameters, S 1zz, (S 1xx - S 1yy), S 2zz and (S 2xx - S 2yy). The experimental results are interpreted using a recently proposed mean field theory of binary mixtures of biaxial molecules.1 In the geometric mean approximation all particles couple to an identical mean field and the parameters of the theory are the ratios of intermolecular interaction strengths of the pure materials. There is good agreement between the predictions of theory and the four component order parameters determined from 2H-NMR experiments, over the entire temperature range studied. Thus this description is capable of predicting the temperature dependence and interrelation of the nematic orientational order parameters for both components of the mixture. Analogous calculations on data from pure FLOC14 2 gives a ratio of interaction strengths consistent with that obtained from the binary mixture.

Experimental deuteron magnetic resonance study of orientational order in the nematic phase of a binary mixture of biaxial molecules

Deuteron magnetic resonance (2H-NMR) spectra have been obtained from a binary mixture of 2-fluorenyl-4′-tetradecyloxy benzoate-d9 (FLOC14) and para-xylene-d10 (p-xy) as a function of temperature [Hoatson et al. Mol. Cryst. Liq. Cryst. (to be published)]. The liquid crystal FLOC14 is selectively deuterated on the rigid fluorene moiety, while p-xy is perdeuterated. Nonlinear least-squares fits to the quadrupolar splittings νkQ allow unambiguous determination of the temperature dependence of the orientational order parameters Sizz and (Sixx−Siyy) of both species i=1,2. These results are the first to provide information on the degree and asymmetry of orientational order of both biaxial molecules in the uniaxial nematic phase of a binary mixture. The new approach introduced to analyze the experimental data allows for an arbitary orientation of the rigid core relative to the molecular axis. The results demonstrate that the splittings and derived order parameters are insensitive to this twist angle. The experimental results are interpreted using a new mean field theory of binary mixtures of biaxial molecules [Palffy-Muhoray and Hoatson (to be published)]. There is good agreement between the predictions of theory and the component order parameters determined from 2H-NMR experiments, over the entire temperature range studied. Thus this description is capable of predicting the temperature dependence and interrelation of the nematic orientational order parameters for both biaxial molecules in a binary mixture. The derived theoretical parameters are interpreted as the ratios of intermolecular interaction strengths.

On the dynamics of ethene molecules sorbed in the zeolite NaY

The deuteron magnetic resonance spectra of ethene-d 4 sorbed in the zeolite NaY at one molecule/supercage loading level were measured at temperatures between 290 and 78 K. From the solid-state patterns at low and the isotropically averaged singlet spectra at high temperatures, the correlation times of the anisotropic rotation around the twofold symmetry axis normal to the molecular plane as well as of the isotropic site-exchange motion are deduced. The intracrystalline diffusion coefficient is derived as D/ m 2 s −1 = 3.4 · 10 −7 exp( −2000 T K −1 ).

NMR determination of quadrupole coupling constants of deuterons in N,N-dimethylformamide-d 7

The quadrupole splittings in the deuteron magnetic resonance spectrum of N,N-dimethylformamide- d 7 (DMF- d 7) oriented in a nematic phase have been measured in order to determine the quadrupole coupling constants. The elements of the order tensor, S ij 's, necessary for the calculation of the quadrupole coupling constants were obtained by an examination and analysis of the proton spectrum of a mixture of DMF and DMF- d 7 under the same conditions of temperature and concentration. Under the assumption that the field gradient has local axial symmetry, the quadrupole coupling constants (in kilohertz) along the bond axis were determined to be 162 ± 5 for the methyl deuterons trans to the amide deuteron and 161 ± 5 for those cis to the amide deuteron with the assumption of 108.5° for the DCD bond angle within the CD 3 groups. The quadrupole coupling constant of the amide deuteron is sensitive to the assumed model of the methyl rotation; it lies in the range of 154 to 181 kHz.

The high fidelity extraction of weak broad lines from NMR spectra containing large solvent peaks

The detection of a weak broad deuteron magnetic resonance spectrum in the presence of a much larger narrow 2H signal arising from solvent molecules is discussed. This problem is relevant to the study of 2H sites which exchange with the solvent at a rate slow compared to the NMR timescale but sufficiently fast that one cannot use a solvent containing exchangeable protons. A numerical method for 2H 2O solvent line suppression has been developed which employs a computer curve fitting routine to represent the 2H 2O free induction decay by an empirical function (an orthogonal polynomial) which is then subtracted from the total free induction decay. The broad spectrum obtained upon Fourier transformation is undistorted except at frequencies very close to the central frequency. This method is demonstrated to work well in obtaining the broad deuteron magnetic resonance spectrum from exchangeable hydrogens on a small peptide embedded in a phospholipid bilayer when the ratio of integrated intensities of narrow solvent to broad peptide signals is several hundred to one.

Structural phase transition in (ND4)2Se2O5

The first detection of the phase transition of (ND4)2Se2O5 crystal is reported. The dielectric properties, the deuteron magnetic resonance spectra and the proton spin-lattice relaxation time T1 have been measured. A first-order structural phase transition was found. The ammonium groups play an important role in this transition and change their orientation considerably in the unit cell on going through the transition point.

The Deuteron Magnetic Resonance of Tin(II) Chloride Dihydrate Single Crystals in High- and Low-temperature Phases

Abstract The deuteron magnetic resonance spectra of SnCl2·2D2O single crystals have been measured from 208 to 300 K in order to elucidate the static and dynamic structures of water molecules in connection with the phase transition occuring at 234 K. The deuteron quadrupole coupling constants (asymmetry parameters) were determined at 208 K for four non-equivalent water deuterons. These values are 194.2±0.3 (0.066±0.004), 193.2±0.5 (0.112±0.003), 223.3±0.4 (0.206±0.003), and 244.0±0.4 kHz (0.058±0.003), depending largely on the hydrogen-bond strength or the D···O distance. The deuteron arrangements deduced from the EFG tensors agreed well with the ordered structure reported by an earlier ND study. The dynamical process of deuterons responsible for the high-temperature disordered structure was analyzed with the aid of the ND results and was ascribed to a combination of the flip motion of water molecules about each two-fold axis and their rotational motion around each pseudo-three-fold axis.

Isotope effects on the degree of order and the deuterium quadrupole coupling constants, as measured by N.M.R. of oriented benzene-d1, 1,4-benzene-d2and 1,3,5-benzene-d3

Proton and deuteron magnetic resonance spectra of benzene-d 1, 1,4-benzene-d 2 and 1,3,5-benzene-d 3, oriented in various liquid crystal solvents have been analysed. Isotope effects on the degree of order have been measured. The ratios of S-values in the benzene plane are found to be Sxx/Szz =1·0201 ± 0·0009 in benzene-d 1 and 1·0389 ± 0·0004 in 1,4-benzene-d 2 with the deuterons substituted on the z-axis. Deuteron quadrupole coupling constants of 190·4 ± 1·2 kHz and 192·4 ± 1·2 kHz have been obtained for 1,4-benzene-d 2 and 1,3,5-benzene-d 3.

Deuteron quadrupole coupling in KDF 2

The deuteron magnetic resonance spectrum of a polycrystalline sample of KDF 2 has been measured at v L = 41.337 MHz with the help of the solid echo. The deuteron quadrupole coupling constant e 2 qQ/h equals 58 ± 10 kHz and the asymmetry parameter is η = 0.4 ± 0.1. The F-D distance is obtained as 1.13 ± 0.03 Å.

Deuteron and Niobium‐93 Magnetic Resonance Study of Niobium Deuterides

AbstractNiobium deuterides in the composition range NbD0.55–NbD0.88 were investigated by means of deuteron and 93Nb magnetic resonance over the temperature range 4.2–420 K. The β‐α transition, in the temperature range 340–415 K for these compounds, is sharply defined by the extinction of the deuteron quadrupole interaction as well as by the appearance of the central component of the 93Nb spectrum when the cubic α phase is formed. These results are discussed in relation to other determinations of the β‐α transition temperature. No other significant changes in the deuteron magnetic resonance spectrum are observed, down to 4.2 K, at which temperature the quadrupole coupling constants are essentially equal, with an average value, e2qQ/h = 33.0 kHz. The temperature dependent behavior of the 93Nb resonance spectrum indicates that the boundary between the α + β and β regions of the Nb  H(D) phase diagram must pass between the compositions NbD0.78 and NbD0.82 at 300 K. The NMR observations do not furnish positive support for the occurrence of the ζ and ϵ phases nor for the occurrence of the cubic γ phase, but they are not incompatible with the occurrence of these phases. These observations may reflect an intrinsic insensitivity of the deuteron quadrupole interaction to long range ordering of the deuterium in the lattice. Measurements of the 93Nb Knight shift are in close agreement with the shifts obtained in Nb  Mo and Nb  Tc alloys, and suggest that up to this relatively high deuterium content (D/Nb = 0.88) the deuterium continues to yield its electron to the conduction band of the metal.

NMR spectra of pseudotetrahedral molecules dissolved in a nematic liquid-crystal mixture

The proton magnetic resonance spectra for (CH 3) 4C and (CH 3)(CD 3) 3C and the deuteron magnetic resonance spectra for (CD 3) 4C and (CH 3)(CD 3) 3C have been obtained in nematic liquid-crystal mixtures over the temperature range 30 to 70°C. Each solution contained approximately 26 mole% solute, 55.5 mole% butyl- p( p-ethoxyphenoxycarbonyl)phenyl carbonate (BEPC), and 18.5 mole% p-( p-ethoxyphenylazo)-phenyl undecylenate (EPU). Proton-proton dipolar splittings were observed for (CH 3)(CD 3) 3C but not for (CH 3) 4C, while both (CD 3) 4C and (CH 3)(CD 3) 3C showed quadrupolar splittings. Analyses are discussed in which the dipole-dipole and the quadrupolar splittings are assumed to have additive contributions from both molecular alignment and orientation-dependent moleular distortion. The dipolar splittings indicate that the pseudo-C 3 axis of (CH 3)(CD 3) 3C is aligned with the favored direction of the nematic phase.

NMR in paramagnetic LiCuCl 3 · 2H 2O and LiCuCl 3 · 2D 2O

Proton and deuteron nuclear magnetic resonance are studied in single crystals of LiCuCl 3 · 2H 2O and LiCuCl 3 · 2D 2O, respectively, at room temperature. From the proton resonance spectra are deduced the orientations of the proton-proton vectors in the unit cell and the proton-proton distances in the water molecules. Comparison is made with the values derived from the neutron diffraction structure. The deuteron magnetic resonance spectra show that the water molecules are flipping fast at room temperature. The NMR results are combined with the X-ray crystal structure to find the hydrogen atom positions.

Deuteron magnetic resonance of monodeuteroethene: Isotropic and anisotropic phase spectra

Deuteron magnetic resonance spectrum of monodeuteroethene in isotropic phase solution is shown to give the relative signs of the indirect spin-spin coupling constants, while the proton spectrum cannot provide this information. In agreement with previous experimental and theoretical evidence, J gem is found to have the same sign as the two vicinal coupling constants. High resolution deuteron resonance spectra of monodeuteroethene in the nematic phase solution are analysed in terms of the order matrix and quadrupole splitting. The quadrupole coupling constant and the asymmetry parameter are determined by two partly independent methods.

Mesophase structure studies by deuteron magnetic resonance. Observations for the sodium octanoate—decanol—water system

Deuteron magnetic resonance spectra have been measured for samples in the two lamellar phases ( B and D), the tetragonal rod phase ( C) and the C + D two-phase region of the sodium octanoate-decanol-water system. Both continuous wave and Fourier transform techniques were used. The spectra obtained for the C phase samples showed, besides a quadrupole splitting typical for an anisotropic liquid crystalline phase, an isotropic central peak. Similar spectra were obtained for the C + D two-phase region. The NMR results may imply that the C phase is actually an emulsion of the lamellar D phase and the aqueous micellar solution. This is in contrast to previously obtained findings.

Proton and deuteron magnetic resonance of methanes, silanes and GeH3D dissolved in nematic liquid crystals

The proton and deuteron magnetic resonance spectra of CH4, CH3D, CH2D2, CHD3, CD4, SiH4, SiH3D, SiH2D2, SiH3D, SiD4, GeH3D, dissolved in nematic liquid crystals, are reported. It was found that these molecules, which are essentially tetrahedral, exhibit anisotropic interactions and are partially oriented in the nematic phase. This effect is presumably due to slight deformations induced by the anisotropic medium. Some of the aspects related to the interpretation of the results are discussed.

SOLID-LIKE WATER IN CETYL ALCOHOL

Abstract Addition of a small amount of water to cetyl alcohol caused a marked increase of electrical conductivity in the α-state. Deuteron magnetic resonance spectra for the hydrated specimens indicate that the water molecules are contained in a solid-like state and enhance the protonic conduction presumably by the Grotthus mechanism.

Phospholipid hydration studied by deuteron magnetic resonance spectroscopy

Deuteron magnetic resonance spectra were obtained from 2H 2O in mixtures with egg lecithin, egg phosphatidylethanolamine, and ox brain sodium phosphatidylserine. The acid form of phosphatidylserine does not hydrate. Details of the different hydration “shells” were obtained by studying the spectral splittings as a function of 2H 2O concentration. Several different types of water are present, including bulk water (exchanging only slowly with water associated with the lipid), “trapped” water (not present with phosphatidylethanolamine), and up to three types of bound water. The spectral splittings characteristic of each water environment yielded information about the water binding energies and degrees of anisotropy of motion of the phospholipid polar groups; lecithin polar groups have least motional restriction and sodium phosphatidylserine most, while phosphatidylethanolamine binds water most tightly. Spectra of some lecithin and phosphatidylserine dispersions varied with time, due to a slow reorganization of randomly oriented multilamellar regions into longer, more ordered systems, with a length of about 1 μm. At −20°C the timescales of the change were of the order of a week and a month for lecithin and phosphatidylserine respectively. Complex changes in the spectra were observed as the temperature was raised; these are interpreted in terms of changes in the motions of the phospholipid molecules.