Isotope and temperature effects on the optical absorption spectrum of solvated electrons in liquid ammonia

Abstract

Substitution of D and H in ammonia increases the energy of the optical absorption maximum E/sub ..cap alpha../sub max// of solvated electrons by 0.04 eV at 200 to 240 K. The temperature dependence of E/sub ..cap alpha../sub max// may also be slightly larger in ND/sub 3/ (-2.6 MeV/K) than in NH/sub 3/ (-2.4 MeV/K). The bandwidth at half-height W/sub 1/2/ is unaltered by isotopic substitution. The low-energy side of the absorption band has a Gaussian shape. The width parameter of the Gaussian increased slightly with temperature, being g/sub 1/ = 0.010 T/sup 1/2/ eV in both NH/sub 3/ and ND/sub 3/. The high-energy side of the absorption band is neither a Lorentzian nor a single power function of E. If it is expressed by A/A/sub max/ varies as E/sup -..cap alpha../, the value of ..cap alpha.. decreases from 6 in the vicinity of A/A/sub max/ = 0.4 to 3 near A/A/sub max/ = 0.03. The band asymmetry parameter is W/sub b//W/sub r/ approximately equal to 1.35 at 200 to 240 K, similar to that for electrons in water at 300 K. The temperature coefficient -(delta E/delta T)/sub A/A/sub max// of the low-energy side of the band is greater than thatmore » of the high-energy side in ND/sub 3/ and water, and probably also in NH/sub 3/. The optical absorption transitions are different on the two sides of the band.« less