DIELECTRIC-RELAXATION AND LIBRATION SPECTROSCOPY OF SOME ALIPHATIC-KETONES AND THEIR MOLECULAR BEHAVIOR

The dielectric loss in the frequency range 2-150 GHz and the power absorption coefficient from 300 GHz to 6 THz have been measured in dilute solutions of cyclohexane at 20-degrees-C for acetone, hexanone-2, heptanone-2, heptanone-4, nonanone-5, and undecanone-6. Power absorption coefficient for neat acetone and undecanone-6 have also been measured. The results are analyzed in terms of the relaxation and libration processes of molecules. The integrated intensities for diluted and undiluted acetone are higher than calculated by using Gordon's formula by 57% and 90%, respectively. These are interpreted in terms of an enhancement of the effective dipole moment of acetone in its dynamic liquid structure. From extreme dilution of acetone to its neat liquid, the libration frequency increases from 24 to 66 cm-1, whereas the half-power points bandwidth increases similarly from 86 to 115 cm-1. A similar though not so dramatic effect is observed for undecanone-6; the libration frequency increases slightly from 75 to 80 cm-1 for diluted to undiluted solutions. The results show that acetone behaves as a rigid molecule and relaxes predominantly through a tumbling motion of the asymmetric top. The same holds for undecanone-6 but to a lesser degree, whereas for the intermediate members of the family, there is an increased contribution from the intramolecular rotations to the relaxation and libration processes.