Nuclear magnetic relaxation study of the molecular rotations of ethane and propane

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1980

OSTI ID:6246871

McKay, D R

R/sub 1/ relaxation rates for deuterons, protons, and carbon-13 nuclei have been measured in liquid ethane and in the methyl and methylene groups of liquid propane. The proton intramolecular and interintermolecular relaxation rates were separated by the dilution method. The carbon-13 dipolar and spin-rotation relaxation rates were separated by the NOE method. The relaxation rates were measured over the temperature range +20 to -120 degrees centigrade. The carbon-13 and deuteron rates were found to obey the Arrhenius relation. Comparisons of the deuteron rates and the proton rates indicate that the intramolecular relaxation rates of the protons include dipolar and spin-rotation contributions. The deuteron rates indicate that both ethane and propane reorient anisotropically. The data suggest that propane has a rotational anisotropy (..cap alpha..) which varies between one and two from the highest to the lowest temperatures studied. We found that the deuterated molecules reorient more slowly than the undeuterated molecules. Methyl reorientation by internal rotation in propane was found to be much slower than overall reorientation of the molecule. The data for ethane were less sensitive to internal rotation, but indicate that internal rotation is slower than overall reorientation. The correlation times for reorientation of the deuterated molecules were calculated and extrapolated to the undeuterated molecules. These extrapolated correlation times were used to predict relaxation rates for carbon-13 and protons. We found that our predicted and observed rates could not be reconciled without substituting r/sub d/'s, effective inter-nuclear distances for dipolar relaxation, for the commonly used equilibrium distance (r/sub e/'s) in the usual expressions for dipolar relaxation rates.

• Research Organization: Wyoming Univ., Laramie (USA)
• OSTI ID: 6246871
• Country of Publication: United States
• Language: English

Related Subjects

640302* -- Atomic
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
ALKANES
ALKYL RADICALS
ANGULAR MOMENTUM
CARBON 13
CARBON ISOTOPES
DATA
DEUTERIUM
ELEMENTS
ENERGY LEVELS
ETHANE
EVEN-ODD NUCLEI
EXCITED STATES
EXPERIMENTAL DATA
HYDROCARBONS
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
INTERMOLECULAR FORCES
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
METHYL RADICALS
METHYLENE RADICALS
NONMETALS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PARTICLE PROPERTIES
PROPANE
RADICALS
RELAXATION
RESONANCE
ROTATIONAL STATES
SPIN
STABLE ISOTOPES