Effect of Electric Field on Condensed-Phase Molecular Systems

Abstract

In this dissertation, I studied the effect of electric field on a condensed-phase molecular system. Many experiments have been performed for the investigation of field-induced phenomena, but only a few experiments are available for well-defined experimental conditions with strong electric field. We invented the ice film capacitor method, which can apply strong electricfield across a frozen molecular film. The effect of the electric field was examined using this method. Chapter I introduces various experimental methods that are currently used to study field-induced phenomena. The advantages of the ice film capacitor method over other existing technique are briefly mentioned. In chapter II, the experimental methods used for the study in this thesis are explained. The detailed procedure of the ice film capacitor method and the basic principle of reflection absorption IR spectroscopy are introduced. Instrumentation of the methods is also described. In chapter III, the conformational change of 1, 2-dichloroethane (DCE) is investigated under the external electric field. Reflection absorption infrared spectroscopy was used for monitoring the molecular changes such as gauche/trans conversion and the reorientation of gauche-DCE. Trans-DCE molecules converted to gauche-DCE under an external electric field, and this conversion led to the reorientation of gauche-DCE along the electric field. The field-induced changes were occurred at 50 - 90 K, but not at 8 K, indicating that both thermal and electrostatic energies are needed to induce the conformational changes in a frozen molecular film. In chapter IV, the field-induced dissociation of acetic acid (AA) is studied using the ice film capacitor method. The dissociation of acid was monitored by using infrared spectroscopy and the mechanism of field-induced acid dissociation was discussed. AA molecules were dissociated into acetate ions by the external electric field at an acid-base interface. The amount of field-induced dissociation depended on the direction of the applied electric field, which suggests that the reaction was aided by the reorientation of reagent molecules. The effect of molecular size was studied by comparing the results of formic acid and propionic acid with those obtained for AA. The dissociation of smaller acids was more enhanced, supporting our interpretation that field-induced dissociation occurred via molecular reorientation.