Department of physics, Bangalore University.
○RAMU L Chandramani R

Molecular dynamics (Torsional frequencies-f_T) in several organic and inorganic chlorine compounds have been evaluated on the basis of X-ray thermal parameters and Nuclear Quadrupole Resonance data. NQR Studies gives useful information about the molecular dynamics and phase transitions in solids. Usually the f_T obtained through NQR data are compared with FT IR/Raman data. The approach here is to evaluate f_T at room temperature using available data on X-ray thermal parameters.
Temperature factor of an atom for any set of lattice planes (hkl) depends on the inter planar spacing and on the magnitude of vibration perpendicular to the planes. There is an expression [1], which relates general temperature factor, the reciprocal lattice parameters and thermal parameters (U_ij) expressed in terms of mean square amplitudes (<θ²>) of vibration in Pm². The NQR motional averaging has been shown to arise from temperature dependent tilting of the z-axis of the EFG tensor. One can therefore estimate <θ²> for various C-Cl bond directions, which define the respective z-axis of the EFG tensor using the X-ray thermal parameters.
The f_T at T=300K in the following compounds has been done:
(1) 3,4 dichlorophenol.
(2) 4-Chloro-3,5-dimethylphenol.
(3) 2,5-Dichloroaniline.
(4) 5-Chloro-2-Pyridone.
(5) Mercuric Chloride.
(6) Antimony Trichloride.
The f_T obtained by X-ray thermal parameters and by NQR data have been compared. The values obtained in both cases are in good agreement. The above approach is a good illustration of the supplementary nature of the data from X-ray studies in relation to NQR studies of compounds in solid state.
Reference;
1).L.Ramu, R.Banu, S.Rani and R.Chandramani. ACTA PHYSICA POLONICA-A,
775,Vol-109(2006).