Pulse radiolysis of liquids at high pressures. V. Absorption spectrum and yield of the solvated electron in liquid ammonia at 23 °C and pressures up to 6.7 kbar

Abstract

The absorption spectrum and primary yield of the solvated electron in liquid ammonia (eam−) have been determined by nanosecond pulse radiolysis of liquid ammonia at 23°C and pressures up to 6.7 kbar. With increase in pressure from 0.009 kbar (vapor pressure at 23°C) to 6.7 kbar, the following changes occur in the absorption spectrum: The transition energy at the absorption maximum (Emax) increases from 0.67 to 0.91 eV; the observable portion W of the bandwidth at half-maximum, from Emax to the high-energy side of the spectrum, increases by 35%; and optical density at the absorption maximum (ODmax) decreases by 32%. The pressure and temperature dependences of Emax are attributed to changes in (1) size of the electron cavity and (2) the local dielectric constant associated with the solvation shell of the electron. At 23°C and 0 kbar, (∂lnEmax/∂P)T for eam− exceeds that for solvated electrons in water, methanol, and ethanol by a factor of ∼4. Such a result indicates that the cavity of eam−(V̄=98 ml mol−1) is more compressible than that of the electron in water (V̄ = 7 ml mol−1 for eaq−) and the alcohols. From the changes in W and ODmax with increase in pressure from 0.009 to 6.7 kbar, the extinction coefficient at the absorption maximum is estimated to decrease by 19% (similar to the result for eaq−) and the primary yield is estimated to decrease from 3.2 to 2.0 solvated electrons per 100 eV (in contrast with invariance of the eaq− yield). The decrease in primary yield is attributed to an increase in the probability of neutralization relative to separation of geminate NH4+−eam− pairs owing to the large negative activation volume of the neutralization reaction as a consequence of the large volume of eam−.

Pulse radiolytic formation of solvated electrons in hydrazine

“…104 and 1.25 x lo4 M-' at 410 and 640 nm, Consequently we find no evidence for a sigrespectively (35). On this basis we find that nificant difference in the extinction coefficients (14,19,36,37,42), this supports the solutions saturated with sodium hydroxide, assumption that E,-(400 nm band) is 4 x lo4 enhances the yield to GeS = 2.65 0.15. This M-' cm-'.…”

“…This M-' cm-'. value is identical to that observed in aqueous The oscillator strength, f, of the es-absorpsolutions (15) but less than G,,, = 3.2 ob-tion band in hydrazine can be estimated from tained in liquid ammonia (14,19,36,37). the approximation (43).…”

Femtosecond Relaxation Dynamics of Solvated Electrons in Liquid Ammonia

“…[34] Unfortunately, pressuredependent data on the spectral position of the electron resonance in liquid ammonia are far less comprehensive than temperature-dependent data. Therefore, we are currently also working on obtaining a more detailed data set for the complete two-dimensional pressure and temperature dependence of the spectral position of the electron resonance, in an effort to investigate the possible effect of a pump-induced local density jump (1-jump rather than a T-jump) including "bubble" formation, [35] and subsequent "cavity" contraction in liquid ammonia on ultrashort timescales.…”

“…From the few pressure-dependent measurements of the absorption spectrum of the ammoniated electron, a density-dependent spectral shift to higher frequencies of 164 cm À1 mol À1 dm 3 can be derived for a room temperature sample. [34] Lacking at the moment pressure-dependent absorption spectra along the relevant isotherm of À52 8C, one has to assume that the density coefficient for the spectral position is independent of the bath temperature. Then, a pumppulse-induced red shift of 3340 cm À1 is consistent with a decrease in the local solvent density by a factor of two, that is, from the pure liquid density of 41 mol dm À3 at À52 8C and saturation pressure to 21 mol dm…”

Electron Mobilities and Ranges in Liquid Ethers: Ion-like and Conduction Band Mobilities

“…Equation 10 was used to estimate the contribution of conduction bands to electron migration in water;alcohols, and ammonia at -296 K. Values of o were obtained from known spectra (34)(35)(36)(37)(38), and ucbO was taken as 5 lo5 cm2 deg3I2 V-' s -I . The contribution of conduction bands in all these liquids was estimated to be negligible at room temperature and below.…”