Simultaneous Orientational and Conformational Molecular Dynamics in Solid 1,1,2-Trichloroethane

ROMANINI, MICHELA; SERRA, PABLO; MACOVEZ, ROBERTO; TRIPATHI, PRAGYA; TRIPATHI, PRAGYA; TAMARIT, JOSEP LLUIS; TAMARIT, JOSEP LLUIS; MITSARI, EFSTRATIA; ZURIAGA, MARIANO; MITSARI, EFSTRATIA; ZURIAGA, MARIANO; ROMANINI, MICHELA; SERRA, PABLO; MACOVEZ, ROBERTO

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Año: 2018 vol. 122 p. 5774 - 5783

1932-7447

The molecular dynamics in the ambient-pressure solid phase of1,1,2-trichloroethane is studied by means of broadband dielectric spectroscopy and molecular dynamics simulations. The dielectric spectra of polycrystalline samples obtained by crystallization from the liquid phase exhibit, besides a space-charge relaxation associated with accumulation of charges at crystalline domain boundaries, two loss features arising from dipolar molecular relaxations. The most prominent and slower of the two loss features is identified as a configurational leap of the molecules which involves a simultaneous change in spatial orientation and structural conformation, namely between two isomeric forms (gauche + and gauche−) of opposite chirality. In this peculiar dynamicprocess, the positions of the three chlorine atoms in the crystal lattice remain unchanged, while those of the carbon and hydrogen atoms are modified. This dynamic process is responsible for the disorder observed in an earlier X-ray diffraction study and confirmed by our simulation, which is present only at temperatures relatively close to the melting point, starting 40 K below. The onset of the disorder is visible as an anomaly in the temperature dependence of the dc conductivity of the sample at exactly the same temperature. While the slower relaxationdynamics (combined isomerization/reorientation) becomes increasingly more intense on approaching the melting point, thefaster dynamics exhibits significantly lower but constant dielectric strength. On the basis of our molecular dynamics simulations,we assign the faster relaxation to large fluctuations of the molecular dipole moments, partly due to large-angle librations of thechloroethane species.