Quasielastic neutron scattering of liquid A2X2 (A : chalcogen, X : halogen)

Quasielastic neutron scattering measurements were carried out at room temperature for liquid S 2 Cl 2 , S 2 Br 2 , Se 2 Cl 2 and Se 2 Br 2 , which are composed of the molecules having the X-A-A-X type chain unit, X and A being halogen and chalcogen atoms. The measurements were performed at the scattering wave vectors of 0.98, 1.55, 2.32 and 2.66 A -1 by using AGNES spectrometer installed in JAERI. By analyzing the intermediate scattering function, which was obtained by Fourier transform of the observed dynamic structure factor, a fast and a slow relaxation processes have been found. The fast process, whose relaxation time is less than 1 picosecond, may be assigned to fluctuations in the dihedral angle within the molecule, while the slow process, whose relaxation time depends strongly on the molecular weight, may be assigned to the translational diffusion of the molecule.