Optical spectra of electrons solvated in liquid ethers: temperature effects

Abstract

The optical absorption band of electrons solvated in ethers has an approximately Gaussian shape on the low energy side of the absorption maximum. The high energy side is wider and has an approximately Lorentzian shape down to A/Amax ≈ 0.3, then extends into a long tail to high energies. The energy at the absorption maximum EAmax and the Gaussian and Lorentzian dispersion parameters g and l are reported as functions of temperature for electrons in diethyl ether (DEE), di-n-propyl ether (DPE), di-n-butyl ether (DBE), and tetrahydrofuran (THF). The values in eV of the parameters at 180 K are: EAmax = 0.76 in THF, 0.67 in DEE, 0.65 in DPE and DBE; l = 0.32 in THF, DEE, and DPE, 0.39 in DBE; g = 0.19 in all the ethers. The temperature coefficients of EAmax are ∼ −2 × 10−3 eV/K, those of l are −(1 ± 1)10−4 eV/K, and those of g are +4 × 10−4 eV/K. The band becomes less asymmetrical as the temperature increases. To make progress in the theoretical treatment of solvated electron spectra attention should be focussed on the separate values of g and l and their temperature dependences; the width at half height W1/2 thereby loses theoretical significance. The decadic molar absorbancy εmax (M−1 cm−1) is 2.9 × 104 in DEE and DPE, 2.6 × 104 in DBE, and 2.1 × 104 in THF. The oscillator strengths f are 0.7 in the n-alkyl ethers and 0.6 in THF. The value of EAmax in p-dioxane is 0.1 eV greater than that in THF and about 0.2 eV greater than those in the open chain ethers. This agrees with a prediction based upon the relative mobilities of electrons in the ethers.