Diffuse X-ray scattering by 2,3-dimethylnaphthalene

The diffuse intensity distribution of X-rays scattered from a dipolar disor dered single crystal of 2,3-dimethylnaphthalene (2,3-DMN) has been measured and was found to be nearly independent of temperature in some restricted r egions of the reciprocal space. This behaviour was related to a static diso rder of the crystal. Lattice parameters were determined between room temper ature and 9 K and phase transitions at 227 K and 112 K were observed. The r esults of the data analysis at 298 K are: the equivalent isotropic displace ment parameter U-eq for the thermal Debye-Waller factor is (0.18 Angstrom)( 2) the displacement parameters describing the static disorder are U-xx(C) l ess than or equal to (0.05 Angstrom)(2), U-yy(C) = [0.22 (2) Angstrom](2) a nd U-zz(C) = [0.35 (3) Angstrom](2). The molecules show an orientational Ga ussian distribution around the x axis with a width of 5.0 (8)degrees. All t hese results refer to the molecular inertia system. Correlation coefficient s characterizing the mean mutual orientation of neighbouring molecules were determined. The highest correlation coefficient was found along [010]: C = -0.231 +/- 0.004.