Deuteron Magnetic Resonance in a-Si and a-SiGe Produced from Fluorides

ABSTRACTDeuteron magnetic resonance line shapes and spin lattice relaxation times are presented for a-Si:D, F and a-SiGe:D, F. These parameters differ from those for typical a-Si:D, H samples, but in some respects are similar to those for an annealed a-Si:D, H sample. The a-SiGe:D, F spectra display an unusually large broad central weakly bound D resonance component and a barely-resolved Ge-D quadrupolar doublet. Comparisons indicate substantial differences in void morphology between the a-Si:D, F and a-SiGe:D, F.

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A nuclear magnetic resonance investigation of n -pentane, n -hexane and cyclo pentane

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1954.0093 ◽

1954 ◽

Vol 222 (1151) ◽

pp. 526-541 ◽

Cited By ~ 20

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Molecular Motion ◽

Relaxation Times ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Kcal Mole ◽

Second Moment ◽

Spin Lattice ◽

Second Moments

The nuclear magnetic resonance spectra and spin-lattice relaxation times have been measured for the protons in n -pentane (C 5 H 12 ), n -hexane (C 6 H 14 ) and cyclo pentane (C 5 H 10 ) all in the solid state. The temperature range covered was from 70° K to the melting-points of 143·4° K for n -pentane, 177·8° K for n -hexane and 179·4° K for cyclo pentane. In the case of n -pentane and n -hexane the second moments of the absorption lines were found to be smaller than the computed rigid lattice values over the. whole temperature range. Possible molecular motions which might cause this reduction are discussed. It is suggested that the most probable type of motion is reorientation of the methyl groups at the ends of each molecule about the adjacent C—C bonds. An analysis of the spin-lattice relaxation times shows that this reorientation process is governed by an activation energy of 2·7 kcal/mole for n -pentane and 2·9 kcal/mole for n -hexane, values which support the mechanism postulated. At the lowest temperature the absorption lines had not reached their full widths, even though the reorientation frequencies at these temperatures were considerably less than the line-widths. The experimental second moment for cyclo pentane below about 120° K indicates that the lattice is effectively rigid in this temperature region. The uncertainties in both the experimental and theoretical second moments do not allow a distinction to be drawn between the plane and puckered molecular models. At the temperature of the first transition (122·4° K) the line-width second moment and relaxation time all show a sudden decrease. The low value of second moment at the higher temperatures indicates that considerable molecular motion is occurring, the molecules rotating with spherical symmetry. The change in crystal structure at the temperature of the second transition (138·1° K) is thought to be a direct result of this spherical symmetry. As the temperature increases, the results indicate that more molecular motion must be occurring, and it is thought that the rotating molecules are diffusing through the lattice.

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A proton magnetic resonance relaxation study of molecular motions in trimethylamine-borane

Canadian Journal of Chemistry ◽

10.1139/v76-155 ◽

1976 ◽

Vol 54 (7) ◽

pp. 1087-1091 ◽

Cited By ~ 5

Author(s):

T. T. Ang ◽

B. A. Dunell

Keyword(s):

Magnetic Resonance ◽

Proton Magnetic Resonance ◽

Solid Phase ◽

Relaxation Times ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Spin Lattice ◽

Free Induction ◽

Resonance Spin ◽

Resonance Relaxation

Proton magnetic resonance spin–lattice relaxation times T1 have been measured for trimethylamine-borane from 120 to 380 K, a few degrees above the melting point. Minima in T1 at 157 and 259 K are attributed to threefold reorientation of each of the three methyl groups and the borane group and to threefold reorientation of the whole molecule about the B—N axis, respectively. Activation energies for these processes were found to be 3.3 and 6.7 kcal/mol. Abrupt changes in T1 at 350 and 360 K correspond exactly with heat capacity transitions observed by other workers. The time constant for the decay of the free induction signal (FID curve) changes by two orders of magnitude at 360 K. Having a value of some 3 ms above 360 K, it shows that there must be rapid diffusion as well as molecular tumbling in the highest temperature solid phase.

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Nuclear Magnetic Resonance Studies of Molecular Motion in Natural Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3539560 ◽

1963 ◽

Vol 36 (2) ◽

pp. 318-324

Author(s):

W. P. Slichter ◽

D. D. Davis

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Natural Rubber ◽

Molecular Motion ◽

Relaxation Times ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Nmr Studies ◽

Spin Lattice ◽

Nuclear Magnetic

Abstract Nuclear magnetic resonance measurements have been made on natural rubber to examine how frequency, temperature, and crystallinity affect the nuclear relaxation. Moecular motions were studied by observing NMR linewidths and spin-lattice relaxation times at temperatures between −100° and 100° C, and at radio frequencies between 2 and 60 Mc. The effect of crystallinity was seen in measurements on stark rubber. The relation between frequency and temperature in the spin-lattice relaxation process is examined in terms of the Arrhenius equation and the WLF expression. The importance of using frequency as a variable in NMR studies of molecular motion is stressed.

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