Effect of Electric Field on Condensed-Phase Molecular Systems. I. Dipolar Polarization of Amorphous Solid Acetone

摘要

We investigated the dipolar reorientation of acetone molecules in amorphous solids under the influence of externally applied electric fields in the range of (0-4.3) x 10(8) V.m(-1). The electric field was applied using an ice film capacitor method, and the field strength was estimated from measurements of the film voltage and thickness using a Kelvin probe and the temperature-programed desorption method, respectively. Reorientation of the acetone molecules was monitored with reflection-absorption infrared spectroscopy (RAIRS), which measured the absorbance change of the acetone vibrational bands induced by the applied electric field. The electric field caused a substantial degree of dipolar polarization of the sample. Acetone molecules were reoriented toward the field direction by an average angle of about 31 degrees at an applied field strength of 4.3 x 10(8) V.m(-1), according to analysis of the RAIRS intensity changes using a simple molecular geometry model. While the extent of dipolar polarization of the sample increased with increasing field strength, the sample was not reversibly depolarized with decreasing field strength. Multiple-peak analysis of the v(C=O) spectrum revealed that the molecules in the acetone-water boundary region were more easily rotated compared to those in the bulk.