Composition effects on optical absorption spectra of solvated electrons in alcohol/water mixed solvents

Abstract

AH-DONG LEU, KAMAL N. JHA, and GORDON R. FREEMAN. Can. J. Chem. 60,2342 (1982. Addition of a few percent of water to an alcohol has a relatively large effect on the shape of the optical absorption spectrum of solvated electrons in the liquid. This occurs whether the optical absorption energy in the pure alcohol is greater or smaller than that in water. Addition of up to 10mol% of water causes E,,,, in methanol and primary alcohols to decrease, while it increases in secondary and tertiary alcohols. At around 10mol% water in primary alcohols E,,,, passes through a minimum and increases again at higher water concentrations, reaching a plateau at about 30 mol% and remaining constant up to about 95 rnol% water; over the last part of the composition range to pure water E,,,, decreases slightly. The behavior in secondary and tertiary alcohols containing >30mol% water is similar to that in primary alcohols. The width of the band at half height W,,, is divided at E,,,, into "red side" and "blue side" portions W, and Wb, respectively. In methanol and in primary and secondary alcohols, addition of up to 30 mol% of water greatly reduces Wb but has relatively little effect on W,. At >30 mol% water Wb and W, are similar to those in pure water. In tertiary butyl alcohol the band width is similar to that in pure water, so addition of water to the alcohol makes little change in the band width. The waterlalcohol composition effects on the e; absorption band parameters are attributed to changes in solvent structure. This is especially evidenced by the minimum in E,,,, at 10 mol% water in a primary alcohol. The changes in band asymmetry Wb/ W, indicate that the types of electronic transition on the low and high energy sides of the band are different. Introduction structure. Simons and co-workers have formulated The energy levels of solvated electrons, as the problem (3, 4), appropriately introducing the reflected in the energy of the optical absorption effects of fluct~ations in solvent properties at an maximum EAmax, are determined more by details of early stage of the model. Ultimately it was not the liquid structure than by the dielectric constant possible to use realistic Structure properties in the or the molecular dipole moment (l,2). The breadth ~alcdations-For example, the orientational

Effects of solvent structure on electron reactivity and radiolysis yields: 2-propanol/water mixed solvents

“…Similar dependence of GE,,,, on the composition of water alcohol mixtures has been observed by Leu and Jha (23b) in methanol, ethanol, and I-propanol. The initial increase of GE,,, values correlates with a small increase of the energy of the peak of the e-, spectrum, E,,,,, for small amounts of alcohol in water (22). The maximum in the plot of GE,,, against mixture composition is the most pronounced for 1-P~OH, and so is the increase of E,,,,.…”

“…The activation energy and entropy have minima at between 15 and 8 mol% water. The minima cannot be explained on the basis of changes in E,, which decreases monotonically in this concentration range (22,23). However, between 0 and 10 mol% of water in 2-PrOH there is a sharp decrease of W,, the portion of the width at half height on the blue side of E,,,, (22).…”

“…The minima cannot be explained on the basis of changes in E,, which decreases monotonically in this concentration range (22,23). However, between 0 and 10 mol% of water in 2-PrOH there is a sharp decrease of W,, the portion of the width at half height on the blue side of E,,,, (22). The quantity Eb = E,,,, + Wb has a minimum at 10 mol% water (22,23).…”

“…In this laboratory, various aspects of electron behaviour in hydroxylic solvents have been studied (16)(17)(18)(19)(20)(21)(22)(23)(24). Recently (22,23) it was found that the optical absorption spectra of solvated electrons in alcohol-water mixtures display a strong composition dependence, which was attributed to changes in solvent structure.…”

“…Recently (22,23) it was found that the optical absorption spectra of solvated electrons in alcohol-water mixtures display a strong composition dependence, which was attributed to changes in solvent structure. O n e might therefore expect to find changes in ' Financially assisted by the Natural Sciences and Engineering…”