Spectroscopic and differential scanning calorimetric studies of the phase transitions in oxanorbornane

1998 ◽  
Vol 76 (10) ◽  
pp. 1365-1370 ◽  
Author(s):  
Ralph M Paroli ◽  
Denis FR Gilson ◽  
Ian S Butler
Keyword(s):  
Phase Transitions ◽  
Group Analysis ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Factor Group ◽  
Spin Lattice Relaxation ◽  
Differential Scanning Calorimetric ◽  
Spin Lattice ◽  
Calorimetric Studies

Oxanorbornane (7-oxabicyclo[2.2.1]heptane, C6H10O) resembles other bicycloheptane-like molecules by exhibiting order-disorder transitions in the solid state. Differential scanning calorimetric studies show that five different phases may occur, with hysteresis in the transition temperatures. The vibrational spectra have been examined, and a factor group analysis of the vibrational splittings indicates that the crystal structure of the ordered phase has D2d symmetry. Activation energies for molecular motions were derived from proton spin-lattice relaxation time measurements.Key words: oxanorbornane, order-disorder, phase transitions.

Proton Spin Lattice Relaxation in the Dimethylammonium Group

1993 ◽  
Vol 48 (5-6) ◽  
pp. 713-719
Author(s):  
K. Venu ◽  
V. S. S. Sastry
Keyword(s):  
Experimental Data ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Dipolar Interactions ◽  
Spin Temperature ◽  
Spin Lattice ◽  
Molecular Group

Abstract A model for the spin lattice relaxation time of the protons of dimethylammonium in the Redfield limit and common spin temperature approximation is developed. The three fold reorientations of the methyl groups, the rotation of the whole molecular group around its two fold symmetric axis and possible correlations among these motions are considered. The effect of these processes on the dipolar interactions among the protons within the same molecular group is taken into account. The resulting relaxation rate is powder averaged and used to explain the experimental data in literature on [NH2(CH3)2]3Sb2Br9 . The analysis shows that dynamically inequivalent groups exist in this compound and that the effect of proposed correlation among the different motions on the final results is negligible.

NUCLEAR MAGNETIC RELAXATION IN GAS MIXTURES

1962 ◽  
Vol 40 (8) ◽  
pp. 1027-1035 ◽  
Author(s):  
D. Llewelyn Williams
Keyword(s):  
Room Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Gas Molecules ◽  
De Broglie Wavelength ◽  
Diffraction Effects ◽  
Good Agreement

Measurements of the proton spin–lattice relaxation time using pulse techniques have been made on the hydrogen–nitrogen, hydrogen–neon, and hydrogen–helium systems from room temperature to 60° K. The results are in good agreement with the Oppenheim–Bloom theory and illustrate the importance of the radial distribution of the gas molecules and of diffraction effects associated with the de Broglie wavelength.

Surface Induced Spin-Lattice Relaxation of Water in Tricalcium Silicate Gels

1991 ◽  
Vol 46 (8) ◽  
pp. 697-699
Author(s):  
F. Milia ◽  
Y. Bakopoulos ◽  
Lj. Miljkovic
Keyword(s):  
Grain Size ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Tricalcium Silicate ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Water Proton ◽  
Hydration Time ◽  
Spin Lattice ◽  
Stage Process

AbstractThe water proton spin-lattice relaxation time and recovery function of exchangeable water was measured in tricalcium silicate (C3S) gels. The measurements were carried out as a function of the hydration time and grain size. Results show that the hydration of (C3S) is a two stage process. A model is developped

Incommensurability and Domain Structure of K2SbF5

2002 ◽  
Vol 57 (6-7) ◽  
pp. 456-460
Author(s):  
A. M. Panich ◽  
L. A. Zemnukhova ◽  
R. L. Davidovich
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Relaxation Measurements ◽  
Increasing Temperature

Phase transitions and incommensurability in K2SbF5 have been studied by means of 123Sb NQR spectra and spin-lattice relaxation measurements. The phase transitions occur at 117, 135 and 260 K. The line shape and temperature dependence of the spin-lattice relaxation time T1 at 135 to 260 K are characteristic for an incommensurate state with a plane wave modulation regime. At 117 to 135 K a distinct fine structure of the NQR spectra has been observed. The X-ray diffraction pattern of this phase is interpreted as a coexistence of two modulation waves along the a and b axis with wave vectors (a*/6 + b*/6) and (a*/2 + b*/2), respectively. The best interpretation that fits our NQR data is a coexistence of two domains, the structures of which are modulated with different periods in such a manner that each domain exhibits only one of the aforementioned modulation waves. Redistribution of line intensities with the variation of temperature shows that one of the domains becomes energetically preferable on cooling and is transformed into the low temperature phase at 117 K. The 123SbNQR measurements in K2SbF5 show unusually short values of T1, which become close to the spin-spin relaxation time T2 with increasing temperature. - Pacs: 61.44.Fw, 64.60, 64.70, 64.70.Rh, 76.60

Sign in / Sign up

Export Citation Format

Share Document