SCHEDULED MAINTENANCE
Dynamic disorder in acenaphthylene. A solid state deuterium NMR study
Abstract
The dynamic disorder in solid acenaphthylene has been studied by
deuterium NMR spectroscopy of deuteriated powder samples. The spectra
exhibit lineshape and relaxation discontinuities in the transitions from
Phase III, through Phase II, to Phase I (the latter being stable above
127 K). A detailed analysis of the lineshape and T1
relaxation in Phase I is presented. The results show the occurrence of
two distinct equally populated, dynamic sites. The molecules in both
sites undergo planar reorientation, but with different Arrhenius kinetic
parameters:
ko1 = 1.5 ×
1012 s-1,
ΔE1 = 10.2 kJ
mol-1;
ko2 = 4.8 ×
1012 s-1 and
ωE2 = 18.3 kJ
mol-1. The results are consistent with earlier proton
second moment and relaxation measurements and provide additional
information on the nature of the motion. It is argued that the
subspectra with the slower and faster motions are associated,
respectively, with the (A,B) and C layers in the crystal.
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