R. Vold, G. Hoatson, R. Subramanian
Jun 4, 1998
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0
Influential Citations
21
Citations
Journal
Journal of Chemical Physics
Abstract
The orientation dependence of deuteron relaxation times of Zeeman (T1Z) and quadrupole (T1Q) order have been measured in the temperature range −30 to +45 °C for polycrystalline urea inclusion compounds containing alkyl deuterated octanoic acid-d18, dodecanoic acid-d23, and hexadecanoic acid-d31. These data were fitted to a model, based on Redfield relaxation theory, which incorporates rapid rotation about the long molecular axis and slower, limited angle libration of individual CD bonds about a perpendicular axis. The activation energies for rotational diffusion about the long axis are 17.4±0.8 kJ/mol for octanoic acid-d18, 14.4±0.6 kJ/mol for dodecanoic acid-d23, and 22.5±0.4 kJ/mol for hexadecanoic acid-d31 guests. These values are larger than those for alkane guests with the same number of carbon atoms, and they increase more rapidly with increasing chain length. Quadrupole coupling constants, determined at room temperature from measurements on large single crystals, are consistent with a small gauche ...