NMR Spin-lattice Relaxation Times Research Articles

Effects of Annealing Time and Temperature on Hydrogen in Doped and Intrinsic Amorphous Silicon

ABSTRACTThe local environment and diffusion of hydrogen in hydrogenated amorphous silicon (a-Si:H) depend on both temperature and doping. Previous studies of hydrogen evolution indicate that the manner in which hydrogen diffuses and desorbs from the material depends on doping and may occur at relatively low temperatures over extended time frames. We have examined the microstructure of hydrogen in intrinsic, boron doped and phosphorous doped a-Si:H as a function of annealing temperature and annealing time using hydrogen NMR. Changes in both the H NMR spectrum and spin-lattice relaxation times occur. We find annealing time has only a small effect on these parameters, whereas the annealing temperature has a substantial effect. The bonded-H content drops and the molecular-H2 content is seen to decrease slightly as the samples are annealed to higher temperatures. However the bonded-H remains essentially constant for long time, low-temperature anneals, while the molecular-H2 content is also seen to diminish slightly. The changes are more profound for B-doped samples than for P-doped or intrinsic material, consistent with the conclusions of other studies.

Novel ionic plastic phase of [(CH3)4N]SCN obtainable above 455 K studied by proton magnetic resonance, electrical conductivity and thermal measurements

A new high-temperature solid phase of tetramethylammonium thiocyanate has been found above the phase transition at 455 K, where a large entropy change (15 J K–1 mol–1) was observed. X-ray powder patterns recorded at ca. 470 K showed that this phase forms a CsCl-type cubic lattice with aO= 600 pm, indicating that the SCN– anions take highly disordered orientations. The presence of rapid three-dimensional self-diffusion, as well as the overall rotation of the cations in this phase, was revealed by the measurements of 1H NMR spin–lattice relaxation times, T1 and T1ρ, the second moment of NMR absorptions and the electrical conductivity. The large ionic-diffusion constant (of the order of 10–13 m2 s–1) obtained around 490 K is roughly the same as those reported for ‘ionic plastic’ crystals. An activation energy of ca. 110 kJ mol–1 was determined for cationic self-diffusion. These results imply that this new phase is the first example of an ionic plastic crystal containing tetramethylammonium cations.

ChemInform Abstract: Identification of a Defect Chain Motion in n‐Alkanes by Means of NMR Spin‐Lattice Relaxation Time Measurements

ChemInformVolume 21, Issue 52 Physical Organic Chemistry ChemInform Abstract: Identification of a Defect Chain Motion in n-Alkanes by Means of NMR Spin-Lattice Relaxation Time Measurements I. BASSON, I. BASSON Dep. Phys., Univ. S. Afr., Pretoria 0001, S. Afr.Search for more papers by this authorE. C. REYNHARDT, E. C. REYNHARDT Dep. Phys., Univ. S. Afr., Pretoria 0001, S. Afr.Search for more papers by this author I. BASSON, I. BASSON Dep. Phys., Univ. S. Afr., Pretoria 0001, S. Afr.Search for more papers by this authorE. C. REYNHARDT, E. C. REYNHARDT Dep. Phys., Univ. S. Afr., Pretoria 0001, S. Afr.Search for more papers by this author First published: December 25, 1990 https://doi.org/10.1002/chin.199052044Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume21, Issue52December 25, 1990 RelatedInformation

Preparations, physical properties and reactivities of the lithium potassium salts of tartaric acid (anhydrous and hydrated)

Lithium potassium tartrate hydrates constitute a set of crystalline compounds that contain identical functional groups which are arranged differently in space and which result in different distributions of bonds that retain the water molecules of crystallisation. The preparations, physical properties and reactivities of the d , dl - and meso -salts are described together with results of measurements of TGA, IR spectra, XRD patterns and NMR spin-lattice relaxation times. From these observations, four different crystal structures were distinguished and four distinct hydrates recognized for which the dehydrations proceeded in appreciably different temperature intervals. The anhydrous residues also exhibit variations in structure.

Electrical conductivity due to ammonium ion transport in (NH 4) 3[MF 6] (M:Al, Ga, In) and (NH 4) 2K[AlF 6] crystals

The electrical conductivity σ of (NH 4) 3[AlF 6] and (NH 4) 2K[AlF 6] was measured from room temperature to ca. 400 K by an ac complex impedance analysis. The conductivity of each complex obeyed the Arrhenius relation, σT =σ 0 exp (−E a RT ) . The σ value at 320 K and the E a value are 3.0×10 −4 and 29 and 1.0×10 −6 S m −1 and 69 kJ mol −1, respectively, in the order given above. 1H and 19F NMR second moment and spin-lattice relaxation time measurements on (NH 4) 3[AlF 6] confirmed that the electrical conduction is attributable to the self-diffusion of NH + 4 ions. The results obtained are compared with those of (NH 4) 3[GaF 6] and (NH 4) 3[InF 6] recently reported. The high σ values for these complexes are related to their crystal structures and anionic reorientational motions.

Thallium Nuclear Magnetic Relaxation in Solid Thallium (I) Thiocyanate TlSCN: Phase Transition and Ionic Motion

Abstract The NMR spin-lattice relaxation time (T1) and linewidth parameter (T2*) of 203Tl and 205T1 in solid T1SCN were measured from 290 K up to the melting point (Tm = 507 K). The nonexponential magnetization recovery of could be characterized by a short (T1 s) and a long (T1 1) component. T1 1 showed a T-2 dependence below ca. 350 K in the orthorhombic phase (T<Tc = 371 K) and a minimum in the tetragonal phase (Tc<T<Tm), which were interpreted in terms of lattice vibrations and head-to-tail flips of the linear SCN- ions, respectively. A broad minimum of 77 around 360 K was explained in terms of indirect nucleus-electron scalar coupling between 203Tl and 205Tl, modulated via the anionic flips occurring in the symmetric and asymmetric potential fields for the highland low-temperature phase, respectively. The phase transition is closely related to dynamical disorder of the anionic orientations. At higher temperatures, translational self-diffusion of Tl+ was evidenced by the T2* and T1 s results

Carbon‐13 NMR spin–lattice relaxation time study of the molecular motions of 5‐nitro‐2‐(2‐pyridinylthio)pyridine

AbstractThe motional behaviour of 5‐nitro‐2‐(2‐pyridinylthio)pyridine (NPTP) was ananlysed by 13C NMR spin‐lattice relaxation times (T1). The analysis of the experimental T1 data was performed by using an analytical model to describe the overall and internal motions fo the molecule. The results showed that on exchange exists between the two ‘enantiomeric’ preferred conformations of the molecule, which therefore assumes an enhanced conformationally rigid character in the liquid phase. The motional parameters, derived by the fitting procedure of the relaxation times, showed that strong intermolecular interactions occur in the liquid phase for NPTP and that, in particular, the dipole moment of the mitropyridine ring contributes greatly in determinating the motional dynamics of NPTP.

High‐field multinuclear magnetic resonance relaxation studies of pivalic acid in liquid and solid phases

AbstractProton, 13C, deuteron and 17O NMR line widths and spin‐lattice relaxation times (T1) were measured at a field strength of 9.4T over a wide temperature region in liquid and solid pivalic acid (PA). A striking feature of the NMR spectra is that the methyl proton signal is much wider than the carboxyl proton signal in solid I, whereas the opposite is true for the corresponding deuteron signals. Molecular self‐diffusion and overall molecular tumbling with activation energies of 59 and 31 kJ mol−1, respectively, are responsible for the considerable line narrowing observed for the methyl proton and deuteron resonances in solid I. The narrow carboxyl proton resonance and the low activation energy for the motional narrowing process (18 kJ mol−1) indicate that the acid hydrogen is moving through the lattice at a much faster rate than the rest of the molecule.An analysis of the T1 relaxation times of PA is reported. Rotational correlation times and activation parameters for the overall tumbling, and also the internal methyl and tert‐butyl reorientations (C3 and C3′ motions) taking place in the liquid and solid phases of PA, have been obtained for the first time. The results show that the slower motion is overall tumbling with an activation energy of 20–32 kJ mol−1, while the faster motions are internal C3′ and C3 reorientations with activation energies of 10–15 kJ mol−1. On freezing, the rate of overall tumbling is reduced by a factor of 47 from 1.6 × 1010 to 3.3 × 108 s−1, whereas the rates of C3′ and C3 rotations (1.1 × 1011 and 3.2 × 1010 s−1, respectively) are hardly affected.

Density Profile of Terminally Adsorbed Polymers

Abstract : Specifically labelled terpolymers of 2-vinylpyridine, styrene and deuterostyrene have been prepared by anionic polymerization. The deuterostyrene was deuterated in the methine position and positioned either in the middle or at the end of the triblock terpolymer. The moderately low molecular weight polymers (ca. 20,000 g.mol, polydispersity ca. 1.4) were then adsorbed onto high surface area silica. The environment of the styrene segments in the terpolymer attached to the silica surface and swollen with toluene was probed with deuterium NMR. Comparison of deuterium NMR spin lattice relaxation time, T1 for the adsorbed polymer to that of the polymer in solution suggests that the local concentration of styrene segments near the middle of the polymer, i.e. next to the vinylpyridine segments, is about 0.11 g/ml. Keywords: Polymers; Surface; NMR; Molecular motion; Colloidal stability.

1H NMR Study of the Motion of Guanidinium Ions in Guanidinium Dichloroiodate(I) and Tetrachloroiodate(III)

The temperature dependence of the 1H NMR spin-lattice relaxation time, T1, was measured for C(NH2)3ICl2 and C(NH2)3ICl4. For the dichloro complex, three T1 minima were observed and assigned to the reorientations of crystallographically inequivalent C(NH2)3+ ions about the three-fold axes, each of which has an activation energy of 21, 15, and 8.4 kJ mol−1. The tetrachloro complex yielded a single T1 minimum with an activation energy of 33 kJ mol−1. A phase transition in C(NH2)3ICl2 was found at 399 K by NMR and differential thermal analysis.

13C NMR studies of the solution molecular dynamics of tricyclic antidepressants

Abstract13C NMR spin–lattice relaxation times (T1s) and nuclear Overhauser enhancements (NOE's) were measured for a series of clinically used tricyclic antidepressants (TCAs), imipramine (1), amitriptyline (2), doxepin (3) and dothiepin (4), at two magnetic field strengths (corresponding to 13C frequencies of 75 and 100 MHz). The measurements were carried out at a range of solution concentrations in CDCI3 and D2O in order to determine the factors that influence overall and internal molecular dynamics in these systems. Both the hydrochloride salts and free bases were examined. For solutions in CDCI3 over a range of concentrations, or for low‐concentration (0.03 M) solutions in D2O, T1 and NOE measurements were independent of magnetic field strength, indicating that motion of the TCAs was in the ‘extreme narrowing limit.’ In contrast, for 0.3 M solutions of the hydrochloride salts in D2O, T1 and NOE measurements were field dependent, indicating the presence of significantly slower molecular mobility. It is proposed that micelles are present at this concentration and are responsible for reduced overall tumbling of the TCAs. Several degrees of internal motion were detected by the relaxation and T1 measurements, viz. rapid flexing motion of the benzylic bridging carbons in the central seven‐membered ring and segmental motion of the side‐chain. From an examination of the effect of solvent, concentration and protonation state of the side‐chain on the latter motion, it was possible to derive information on side‐chain conformations and interactions.

Preliminary observations on high-resolution nuclear magnetic resonance for liquids subjected to ultrasound

The perturbation of normal molecular motion in the liquid phase by ultrasound has been detected through its effects on NMR spin–lattice relaxation times, T1. Ultrasound modifies T1 in the opposite sense to that caused by a direct increase in temperature.

NMR studies of molecular motion in tetramethylammonium hydroxide pentahydrate

Polycrystalline (CH3)4NOH·5 H2O (I) and (CH3)4NOD·5D2O (II) have been studied by1H NMR lineshapes, second moments and spin-lattice relaxation times and by2H NMR lineshapes as a function of temperature. From low temperatures the first motion to occur is reorientation of the internally rigid (CH3)4N+ ion about a uniqueC3′ axis (Eta = 8.37 kJ/mol forI,Ea = 9.00 kJ/mole forII), followed closely by pseudo isotropic reorientation of the whole ion (Ea = 18.10 kJ/mol). Motion of the cage molecules (water and hydroxide ion) occurs at higher temperatures with an apparentEa = 11.30 kJ/mol. There is some evidence of a phase transition inII but notI in the 220–230 K region.2H NMR lineshapes ofII below 220 K indicate static cage molecules. Some of the2H quadrupole coupling constants derived from these spectra correspond to O·O hydrogen-bond distances which are incompatible with the known room temperature structure ofI. Above the possible transition inII the anisotropic2H lineshapes indicate rapid motion of2H among all possible hydrogen-bond sites via transfer along the bonds and molecular reorientation. This motion persists in the high temperature phase but the lineshape becomes isotropic due to the cubic symmetry of this phase. It is possible that1H or2H tunnelling plays an important part in the motion of the cage molecules and the different phase behaviour ofI andII.

Studies of the anisotropic self-diffusion and reorientation of butylammonium cations in the rotator phase of butylammonium chloride using 1H magnetic resonance, electrical conductivity and thermal measurements

Butylammonium chloride crystals annealed by slowly scanning through the phase transitions many times have been shown to exhibit a simple thermogram, having a single phase transition at 241 K (Ttr) on heating from ca. 100 K up to the melting temperature Tm(487 K). Another additional thermal treatment was made on the annealed crystals, then measurements of 1H NMR spin–lattice relaxation times T1, T1ρ and the second moment M2 were measured over the same temperature range. These results showed that the cationic axial reorientation mainly contributes to 1H T1 around room temperature, while the cationic self-diffusion plays an important role in the high-temperature range near Tm. AC electrical conductivity measurements on single crystals revealed that ionic conduction takes place in the 2D layers of the room-temperature phase (rotator phase) which have a lamellar-type double-layer structure. The observed T1 and T1ρ data were explained well by applying the theory of 2D diffusion by MacGillivray and Sholl in the low vacancy concentration limit. The average jump times for the cationic self-diffusion were derived from T1 and T1ρ data to be 5 × 10–3 s at room temperature and 3 × 10–7 s at Tm. The transition entropies at Ttr and Tm determined by differential scanning calorimetry were 26 and 19 J K–1 mol–1, respectively. These results imply that the rotator phase is a kind of plastic crystal.

Structural Phase Transitions and Cationic Motions in Pvridinium Dichloroiodate(I) as Studied by 1H NMR, Differential Thermal Analysis, and Powder X-Ray Diffraction

For crystals of pyridinium dichloroiodate (I), (pyH)ICl2, the temperature dependences of the 1H NMR spin-lattice relaxation time T1 and the 1H second moment M2 were determined. M2 was found to be small (~ 1 G2) above room temperature, indicating that the cations perform rapid reorientational motion about their pseudohexad axis perpendicular to the cationic plane. 1H T1 at its minimum was unusually long, indicating this motion occurring in the low symmetry local environments. Phase transitions between stable solid phases were revealed at 282 and 373 K by the 1H NMR measurements and differential thermal analysis. The highest-temperature phase was easily supercooled and transformed reversibly into another metastable phase and back on cooling and warming at almost the same temperature of 138 K. The kinetics of the phase transition from the supercooled to the stable phase at room temperature was analyzed using an Avrami type relation. The growth time of the stable phase was estimated to be about 14 h at room temperature

Regional effects of repetition time on NMR quantitation of water in normal and edematous lungs.

It is well known that pulmonary edema is, in general, spatially nonuniform. Since the NMR spin-lattice relaxation time (T1) is increased by lung edema, the spatial distribution of T1 will be nonuniform. When the repetition time (TR) is short relative to the T1 of edematous lung, lung water content will be underestimated and this underestimation will be spatially nonuniform as well. Therefore, technical artifacts which are a complex function of lung edema and its spatial distribution are expected. We compared overall and regional (topographic) lung water density measurements obtained from living rats (with normal or edematous lungs) using repetition times of 2.0 and 6.2 s (at a magnetic field of 1 T), to quantify this uneven T1 effect for normal and edematous lungs. NMR measurements at TR = 2.0 s underestimated whole lung water density (-rho H2O) TR = 6.2 s) by an average of 7.2% in normal rats and 22.5% in rats with pulmonary edema. Regional -rho H2O underestimation (%delta-rho H2O) varied from 2.2 to 8.8% (groups means) in normal lungs and from 7.3 to 30.8% in edematous lungs. As a result, the interquartile range (of the voxel distribution as a function of rho H2O) underestimated the spatial nonuniformity of lung water density by 28.0% in edematous lungs, likely because of greater loss of NMR signal from high-water-density, long-T1 lung regions. Both %delta-rho H2O and T1 were significantly correlated with -rho H2O at TR = 6.2 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced intrachain spin diffusion in trans-polyacetylene due to sp3 orbital defects.

Samples of trans-polyacetylene, modified with deuterium in such a way as to produce ${\mathrm{sp}}^{3}$ orbital defects, have been studied by EPR and NMR techniques. Both the EPR linewidth and the NMR spin-lattice relaxation time are found to be temperature dependent for all the samples. Moreover, the EPR lines are motionally narrowed and the NMR relaxation time is relatively short, indicative of soliton spin motion. The temperature dependence of the soliton diffusion rate is extracted from the data. A simple model to explain the nuclear relaxation rate is proposed. The ${\mathrm{sp}}^{3}$ orbitals reduce the intrachain diffusion of solitons by 2 orders of magnitude, so that one-dimensional behavior is no longer observed.

Interaction of abscisic acid with phospholipid membranes

The plant hormone abscisic acid (ABA) is shown, under certain conditions, to greatly enhance the permeability of phospholipid bilayer membranes to the nonelectrolyte erythritol (followed spectrophotometrically by osmotic swelling) and the anion carboxyfluorescein (followed by fluorescence). The hormone is ineffective with single- and mixed-component phosphatidylcholine membranes in the liquid-crystalline or gel states. In contrast, substantial ABA-induced permeability is measured for two-component membranes containing lipids with different polar head groups or containing phosphatidylcholines with different acyl chains at temperatures where gel and liquid-crystalline phases coexist. Despite the large ABA-induced enhancement in bilayer permeability, no evidence for a substantial change at the molecular level was seen in the membranes by magnetic resonance techniques. {sup 13}C NMR spin-lattice relaxation times, T{sub 1}, in sonicated unilamellar vesicles and ESR of spin-labeled fatty acids intercalated into membranes showed negligible effect on acyl chain order and dynamics within the bilayer, while {sup 31}P NMR of sonicated unilamellar vesicles indicated negligible effect on molecular motion and conformation in the head-group region. The authors propose that, instead of causing a general nonspecific perturbation to the membrane, the hormone acts at membrane defects formed due to mismatch in molecular packing where two different head groups or acyl chain statesmore » interface. Increased membrane disruption by ABA at these points of membrane instability could then produce an enhancement in permeability.« less

1H and79Br NMR in 1,4-Didecyl-1,4-diazoniabicyclo[2.2.2]octane Dibromide and Diiodide

Temperature dependence of 1H NMR spin-lattice relaxation time was measured in solid 1,4-didecyl-1,4-diazoniabicyclo[2.2.2]octane dibromide and diiodide (C10–DABCO–C10–Br2 and C10–DABCO–C10–I2). 79Br NMR spin-lattice relaxation time and chemical shift measurements in the high-temperature phase were also performed in C10–DABCO–C10–Br2. It was found that the cation rotates isotropically, while the anion diffuses at a correlation time of ca. 10−8 s in the high-temperature phase of C10–DABCO–C10–Br2. The activation energies for these modes are 30 and 34 kJ mol−1, respectively. Methyl reorientation is activated in the low-temperature phase (Ea=11.8 kJ mol−1 in C10–DABCO–C10–Br2 and Ea=12.0 kJ mol−1 in C10–DABCO–C10–I2). Near the phasetransition temperature some motion of decyl chain is observed (Ea=57 kJ mol−1 in C10–DABCO–C10–Br2 and Ea=35.5 kJ mol−1 in C10–DABCO–C10–I2).

Proton NMR study on the molecular motion and conformation of polyaniline doped with HCl

Proton NMR spectra and spin-lattice relaxation time (T1) for polyaniline doped with HCl were measured at 90MHz over a temperature range of 110–430K. A narrow line with a width of about 1–2KHz superimposed on broad NMR peak was observed above 210K, and it was tentatively assigned to the protons in dopant and absorbed water. The analysis of linewidths and second moments for the broad lines reveal two distinct relaxation processes with activation energies of 1.9 and 7.8Kcal./mole,respectively. The former may be associated with the motion of the dopant and water absorbed and the latter with the rotation of benzoid ring about C-N bond axis. The second moment data suggest that the twist angle between the adjacent rings decreases with rising the doping ratio. Proton NMR relaxation rate was fitted with a theoretical equation containing the contributions from nuclear dipolar interaction and from electron-proton interaction, Rd and Rp, respectively.Rd is negligible below room temperature and Rp has little change above 100K. The total relaxation rate is dominated by Rp near room temperature.