R. Julian C. Brown
- B.Sc., 1956, M.Sc., 1959, University of Sydney;
- Ph.D., 1962, University of Illinois;
- Assistant Professor, 1962-66, Queen's University;
- Research Scientist, 1966-69, Australian Atomic Energy Commission.
My research is in the area of the chemical physics of solids, with special interest in solids in which there is disorder. In crystalline ammonium salts the ammonium ion is in a state of rapid rotation at ordinary temperatures, and the interaction between this ion and the surrounding crystal lattice leads to unusual properties. Several ammonium salts have very anisotropic thermal expansion and actually contract in one direction when heated; in some cases the heat capacity shows a broad peak at a characteristic temperature. Anomalies such as these are not found in the alkali metal salts of the same anions, and so must be due to the presence of the ammonium ions. The determination of the underlying mechanism for these anomalies is the object of this program of research.
Nuclear spin relaxation times provide a powerful means of studying the motion of molecules in both the solid and liquid state. Measurements of relaxation times can be made on many nuclei in a magnetic field by standard NMR and nuclear quadrupole resonance (NQR) methods. In collaboration with AECL, Chalk River, neutron diffraction is being used to examine details of the rotational motion of the ammonium ion in crystals which cannot be obtained by X-ray diffraction. The results of these experiments are then compared with theoretical models and molecular dynamics calculations from which detailed structural and spectroscopic information may be calculated.
A. Alavi, R.M. Lynden-Bell, P.A.Willis, I.P. Swainson and R.J.C. Brown: "An ab initio and neutron diffraction study of ammonium chloride". Can. J. Chem. 1998, 76, 1581-1587.
CHEMBOOK, a textbook of general chemistry. R.J.C. Brown. Campus Bookstore, Kingston. 1999.
A. Alavi, R.M. Lynden-Bell, R.J.C. Brown: "Displacement and distortion of the ammonium ion in rotational transitional states in ammonium fluoride and ammonium chloride." J. Chem. Phys. 1999, 110, 5861-5865.
A.Alavi, R.M.Lynden-Bell and R.J.C.Brown. The pathway to reorientation in ammonium fluoride. Chem. Phys. Lett. volume 320, pages 487-491 (2000)
R.J.C. Brown and R.F.C. Brown. Melting point and molecular symmetry. J. Chem. Ed. volume 77, pages 724-731 (2000).
H.F. Shurvell, R.J.C. Brown, P.M. Fredericks and L. Rintoul, The low temperature Raman spectra of polycrystalline NH4F and ND4F. J. Raman Spectrosc. volume 32, pages 219-226 (2001).
A. Alavi, R.M. Lynden-Bell and R.J.C. Brown. Computed vibrational wavenumbers in ammonium fluoride crystals. J. Raman Spectrosc. volume 32, pages 996-999 (2001).