Solvated Electron Pairing with Earth Alkaline Metals in THF 2Reactivity of the (MgII, es-) Pair with Aromatic and Halogenated Hydrocarbon Compounds

Picosecond Pulse Radiolysis Study on the Radiation-Induced Reactions in Neat Tributyl Phosphate

The ultrafast radiolytic behavior of tributyl phosphate, TBP, has been investigated using 7 ps electron pulses with 7 MeV kinetic energy, from which two key species have been observed and characterized: the TBP solvated electron (e_TBP^-) and the TBP triplet excited state TBP* (³a) or its fragmentation products. The e_TBP^- exhibits a broad absorption band in the visible and near-infrared (NIR) spectrum, with a maximum beyond our 1500 nm detection limit. Nitromethane was used to scavenge e_TBP^- to confirm its absorption spectrum and to determine its associated rate coefficient, 1.0 × 10¹⁰ M^-1 s^-1. The electron's molar extinction coefficients were found by an isosbestic method using biphenyl as a solvated electron scavenger. The time-dependent radiolytic yield of e_TBP^- was also determined directly from 7 ps to 7 ns and compared with those in water, tetrahydrofuran, and diethyl carbonate. In less than 10 ns, the decay is not due to the reaction with other solvent molecules and is instead predominantly due to the reactions with cations issued from the proton transfer by the TBP radical cation (TBP^•+). In addition to e_TBP^-, another absorption band, stable up to 7 ns, was identified in the visible range. This has been attributed mainly to the TBP triplet excited state, TBP*(³a), by a combination of molecular modeling methodologies. Interestingly, we did not observe any absorption band in the visible nor in the NIR range arising from TBP^•+. Calculations suggest that TBP^•+ undergoes rapid proton transfer to yield a UV-absorbing species, TBP(-H⁺). Experimental results and supporting molecular simulations provide detailed identification of the earliest species yielded from the radiolysis of neat TBP.

Electron Solvation in Liquid Ammonia: Lithium, Sodium, Magnesium, and Calcium as Electron Sources

A free electron in solution, known as a solvated electron, is the smallest possible anion. Alkali and alkaline earth atoms serve as electron donors in solvents that mediate outer-sphere electron transfer. We report herein ab initio molecular dynamics simulations of lithium, sodium, magnesium, and calcium in liquid ammonia at 250 K. By analyzing the electronic properties and the ionic and solvation structures and dynamics, we systematically characterize these metals as electron donors and ammonia molecules as electron acceptors. We show that the solvated metal strongly modifies the properties of its solvation shells and that the observed effect is metal-specific. Specifically, the radius and charge exhibit major impacts. The single solvated electron present in the alkali metal systems is distributed more uniformly among the solvent molecules of each metal's two solvation shells. In contrast, alkaline earth metals favor a less uniform distribution of the electron density. Alkali and alkaline earth atoms are coordinated by four and six NH3 molecules, respectively. The smaller atoms, Li and Mg, are stronger electron donors than Na and Ca. This result is surprising, as smaller atoms in a column of the periodic table have higher ionization potentials. However, it can be explained by stronger electron donor-acceptor interactions between the smaller atoms and the solvent molecules. The structure of the first solvation shell is sharpest for Mg, which has a large charge and a small radius. Solvation is weakest for Na, which has a small charge and a large radius. Weak solvation leads to rapid dynamics, as reflected in the diffusion coefficients of NH3 molecules of the first two solvation shells and the Na atom. The properties of the solvated electrons established in the present study are important for radiation chemistry, synthetic chemistry, condensed-matter charge transfer, and energy sources.

Nanometer-scale dynamics of charges generated by radiations in condensed matter

The dynamics of short-lived charges generated by pulsed radiations such as electron beam (EB) and photon was investigated to elucidate their reactivity, electronic properties, and spatial behavior on a nanometer scale. Chemical reactions of radical cations (hole) and anions (electron) in condensed matter (organic liquids, polymers, and conjugated materials) occupy an important place in postoptical nanolithography and organic electric devices. The spatiotemporal evolution of charges during geminate ion recombination was measured by a highly improved picosecond (ps) pulse radiolysis and incorporated into a Monte Carlo simulation to clarify the key role of the charges in the formation of latent image roughness of chemically amplified resists (CARs). The dynamics and alternating-current (AC) mobility of transient charge carriers in conjugated materials such as polymer and organic crystals were studied by the combination of microwave conductivity and optical spectroscopies, revealing the potential plausibility for high-performance electric devices. Anisotropy measurement and methodology to resolve the sum of mobility into hole and electron components without electrodes have also been demonstrated.

Solvation dynamics of the electron produced by two-photon ionization of liquid polyols. 1. Ethylene glycol

Solvated electrons have been produced in ethylene glycol by two-photon ionization of the solvent with 263 nm femtosecond laser pulses. The two-photon absorption coefficient of ethylene glycol at 263 nm is determined to be beta = (2.1 +/- 0.2) x 10(-11) m W(-1). The dynamics of electron solvation in ethylene glycol has been studied by pump-probe transient absorption spectroscopy. So, time-resolved absorption spectra ranging from 430 to 710 nm have been measured. A blue shift of the spectra is observed for the first tens of picoseconds. Using the Bayesian data analysis method, the observed solvation dynamics are reconstructed with different models: stepwise mechanisms, continuous relaxation models, or combinations of stepwise and continuous relaxation. Comparison between models is in favor of continuous relaxation, which is mainly governed by solvent molecular motions.

Reactivity between Biphenyl and Precursor of Solvated Electrons in Tetrahydrofuran Measured by Picosecond Pulse Radiolysis in Near-Ultraviolet, Visible, and Infrared

The initial decrease of solvated electrons in tetrahydrofuran (THF) upon addition of biphenyl was investigated by picosecond pulse radiolysis. Transient absorption spectra derived from the biphenyl radical anion (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength region from 400 to 900 nm by the extension of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generation of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anion, C37, which is defined by the solute concentration to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anion and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentrations of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anion accompanying a fast decay component. This observation is discussed in terms of geminate ion recombination, scavenging, delayed geminate ion recombination, and direct ionization of biphenyl at high concentration.