Is molecular rotation really influenced by subtle changes in molecular shape?
In an attempt to seek out whether the reorientation time of a solute molecule is influenced by marginal changes to its shape, rotational relaxation of four coumarin solutes that are almost identical in size but subtly distinct in shape has been investigated in a viscous nonpolar solvent as a function of temperature. It has been observed that the reorientation times of the four coumarins differ significantly from one another. The four solutes have been treated as asymmetric ellipsoids and Stokes-Einstein-Debye hydrodynamic theory has been employed to calculate the shape factors and boundary condition parameters. The measured reorientation times when normalized by respective shape factors and boundary condition parameters can be scaled on a common curve, which is an indication that ellipsoid based hydrodynamic theory is adequate to model the reorientation times even when the differences in the shapes of the solute molecules are minimal.
Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India. gbdutt@apsara.barc.ernet.in
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