Femtosecond Relaxation Dynamics of Solvated Electrons in Liquid Ammonia

Abstract

The ultrafast relaxation dynamics of the well-known solvated electron in liquid ammonia solutions are investigated with femtosecond near-infrared pump-probe absorption spectroscopy. Immediately after photoexcitation, the dynamic absorption spectrum of the electron is substantially red-shifted with respect to its stationary spectrum. A subsequent dynamic blue shift of the pump-probe spectrum occurs on a timescale of 150 fs. The data are understood in terms of ground-state "cooling" and can be quantitatively simulated by an intuitive temperature-jump model employing a dynamically evolving Kubo line shape for the electronic resonance. A simple estimate implies that, on average, the electron in the liquid is coordinated to six nearest-neighbor ammonia molecules. An equivalent analysis of the data based on a bubble-formation/cavity-contraction mechanism is briefly outlined.

Dynamics of Electrons in Ammonia Cages: The Discovery System of Solvation

“…Significantly, the temporal behavior elucidates the predicted theoretical change of the kinetic energy with time, [30] and is on a time scale significantly longer than that of the dissipative dynamics observed in the bulk liquid. [23] The results reported follow the linear dependence for electron binding energy with cavity radius (n À1/3 ), with molecular size n = 20-60, giving the correct slope, in a dielectric solvation model, and the binding energy for bulk media. For lower n clusters, the PE spectra have several peaks, but for larger n only one peak is observed, and we studied the temporal behavior for both ranges.…”

“…In liquids, the only study we are aware of is that reported recently by Vçhringer and co-workers. [23] On the theoretical side, the central issue of electron localization has been addressed by Barnett et al, [24][25][26] while molecular dynamics (MD) simulations by Klein and co-workers [27][28][29][30] have elucidated the time scales of electron dynamics. Electron localization in an internal state occurs for n !…”

Photoinduced Electron Transfer and Solvation in Iodide-doped Acetonitrile Clusters

“…5 Although most of these studies have been carried out in water, experiments have been carried out in other dipolar solvents including alcohols, [6][7][8] ethers, [9][10][11] and other polar molecules. [12][13][14] In several of these experiments, 6,8,11,15,16 solvated electrons were generated by photodetachment of dissolved negative ions, most commonly halide ions, via excitation of charge-transfer-tosolvent (CTTS) bands in which the electron is ejected from the halide into the surrounding solvent. Electron solvation dynamics are detected by changes in the transient absorption spectrum.…”

Femtosecond two-photon ionization of fluid NH3at 9.3 eV

“…Historically, the solvated electron was first discovered in liquid ammonia where it can be prepared chemically by directly dissolving neat alkali metals into the solvent. With the exception of our own work on metal-ammonia solutions [1,2], nothing has been reported so far on the ultrafast relaxation and reaction dynamics of the ammoniated electron. Here, we report on the geminate recombination dynamics of the solvated electron in fluid NH 3 that was generated by two-photon ionization of the pure solvent with 266-nm light.…”