Absorption spectra of trapped electrons in nonpolar glasses: Oscillator strengths and threshold behaviors

Trapped electrons were generated by photoionization of TMPD (N,N,N',N'-tetramethylparaphenylenediamine) and the absorption spectra measured in 2-methylpentane (2MP), 3-methylpentane (3MP), cis-decalin (CD), methylcyclohexane (MCH), and deuterated methylcyclohexane(dh ICH) glasses at 77 K. The low energy absorption fits the Wigner 3/2 power law for threshold photodetachment, consistent with a ground S state with binding energy of 0.48 +/- 0.02 eV and a final continuum P state. For all solvents studied, the maximum absorption cross-section is located at ca. 0.7 eV with an extinction coefficient of 2.7 x 10(4) M-1 cm(-1) (determined by comparison to TMPD cation). From the spectral distribution of the absorption (from 0.5 to 3.3 eV), experimental oscillator strengths were determined to be 0.65(2MP), 0.63(3MP), and 0.76(CD). Various local field corrections to these experimental oscillator strengths are discussed.