James Wishart

Molten salts are crucial materials with exceptional properties that make them suitable for applications such as heat transfer media, coolants, and liquid fuels in molten salt nuclear reactors and the concentrated solar power industry. Understanding their properties requires unraveling the intricate mysteries of their structure. To achieve this, advanced characterization tools are essential. Among various techniques, X‐ray absorption fine structure (XAFS) stands out as a versatile method capable of studying the structure of molten salts under in situ conditions. This review highlights recent advancements in the application of XAFS for investigating the local structure of molten salts, discusses its limitations and potential improvements, and explores complementary approaches such as simulations, machine learning, and correlative experimental methods.

Reactions of Cr(ii) and Cr(iii) with the primary radiolytic transient species (solvated electron and Cl₂˙⁻) in molten eutectic LiCl–KCl were characterized, including the reactivity of their products.

We describe the first implementation of broadband, nanosecond time-resolved step-scan Fourier transform infrared (S²-FT-IR) spectroscopy at a pulse radiolysis facility. This new technique allows the rapid acquisition of nano- to microsecond time-resolved infrared (TRIR) spectra of transient species generated by pulse radiolysis of liquid samples at a pulsed electron accelerator. Wide regions of the mid-infrared can be probed in a single experiment, which often takes < 20–30 min to complete. It is therefore a powerful method for rapidly locating the IR absorptions of short-lived, radiation-induced species in solution, and for directly monitoring their subsequent reactions. Time-resolved step-scan FT-IR detection for pulse radiolysis thus complements our existing narrowband quantum cascade laser-based pulse radiolysis-TRIR detection system, which is more suitable for acquiring single-shot kinetics and narrowband TRIR spectra on small-volume samples and in strongly absorbing solvents, such as water. We have demonstrated the application of time-resolved step-scan FT-IR spectroscopy to pulse radiolysis by probing the metal carbonyl and organic carbonyl vibrations of the one-electron-reduced forms of two Re-based CO₂ reduction catalysts in acetonitrile solution. Transient IR absorption bands with amplitudes on the order of 1 × 10⁻³ are easily detected on the sub-microsecond timescale using electron pulses as short as 250 ns.

Porous materials with high specific surface area, high porosity, and high electrical conductivity are promising materials for functional applications, including catalysis, sensing, and energy storage. Molten salt dealloying was recently demonstrated in microwires as an alternative method to fabricate porous structures. The method takes advantage of the selective dissolution process introduced by impurities often observed in molten salt corrosion. This work further investigates molten salt dealloying in bulk Ni–20Cr alloy in both KCl–MgCl₂ and KCl–NaCl salts at 700 ℃, using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction (XRD), as well as synchrotron X-ray nano-tomography. Micro-sized pores with irregular shapes and sizes ranging from sub-micron to several microns and ligaments formed during the process, while the molten salt dealloying was found to progress several microns into the bulk materials within 1–16 h, a relatively short reaction time, enhancing the practicality of using the method for synthesis. The ligament size increased from ~ 0.7 μm to ~ 1.3 μm in KCl–MgCl₂ from 1 to 16 h due to coarsening, while remaining ~ 0.4 μm in KCl–NaCl during 16 h of exposure. The XRD analysis shows that the corrosion occurred primarily near the surface of the bulk sample, and Cr₂O₃ was identified as a corrosion product when the reaction was conducted in an air environment (controlled amount sealed in capillaries); thus surface oxides are likely to slow the morphological coarsening rate by hindering the surface diffusion in the dealloyed structure. 3D-connected pores and grain boundary corrosion were visualized by synchrotron X-ray nano-tomography. This study provides insights into the morphological and chemical evolution of molten salt dealloying in bulk materials, with a connection to molten salt corrosion concerns in the design of next-generation nuclear and solar energy power plants.

The major societal problem of polymeric waste necessitates new approaches to break down especially challenging discarded waste streams. Gamma radiation was utilized in conjunction with varying solvent environments in an attempt to discern the efficacy of radiolysis as a tool for the deliberate degradation of model network polyesters. Our EPR results demonstrated that gamma radiolysis of neat resin and in the presence of four widely used solvents induces glycosidic scissions on the backbone of the polyester chains. EPR results clearly show the formation of alkoxy radicals and C-centered radicals as primary intermediate radiolytic products. Despite the protective role of the phenyl groups on the backbone of the radiation-induced polyester chains, the radiolytic-glycosidic scissions predominate. Among the following three solvents used in this study (water, isopropyl alcohol, and dichloromethane), the highest radiolytic yield of glycosidic scission was achieved using water. The •OH radicals produced in the radiolysis of phenyl unsaturated polyester aqueous suspensions very rapidly abstract H atoms from the methylene group, which is followed by a very rapid glycosidic scission. The lowest glycosidic yield was found in the dichloromethane solutions of these polyester resins due to scavenging by the fast electron capture reactions.

Primary radiolytic species such as the solvated electron (e_s^–) and Cl₂^•– are key to predicting radiation effects on the long-term behavior of molten salt reactor fuel.

Primary radiolytic species such as the solvated electron (e_s^–) and Cl₂^•– are key to predicting radiation effects on the long-term behavior of molten salt reactor fuel.

Three-dimensional bicontinuous porous materials formed by dealloying contribute significantly to various applications including catalysis, sensor development and energy storage. This work studies a method of molten salt dealloying via real-time in situ synchrotron three-dimensional X-ray nano-tomography. Quantification of morphological parameters determined that long-range diffusion is the rate-determining step for the dealloying process. The subsequent coarsening rate was primarily surface diffusion controlled, with Rayleigh instability leading to ligament pinch-off and creating isolated bubbles in ligaments, while bulk diffusion leads to a slight densification. Chemical environments characterized by X-ray absorption near edge structure spectroscopic imaging show that molten salt dealloying prevents surface oxidation of the metal. In this work, gaining a fundamental mechanistic understanding of the molten salt dealloying process in forming porous structures provides a nontoxic, tunable dealloying technique and has important implications for molten salt corrosion processes, which is one of the major challenges in molten salt reactors and concentrated solar power plants.

Room temperature post-irradiation measurements of diffuse reflectance and EPR spectroscopies were made to characterize the long-lived radiation-induced species formed upon gamma irradiation (up to 100 kGy) of solid KCl, MgCl₂, and ZnCl₂ salts.

Super‐concentrated “water‐in‐salt” electrolytes recently spurred resurgent interest for high energy density aqueous lithium‐ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Herein we investigated LiTFSI/H₂O electrolyte interfacial decomposition pathways in the “water‐in‐salt” and “salt‐in‐water” regimes using synchrotron X‐rays, which produce electrons at the solid/electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X‐ray diffraction. We observed the surface‐reduction of TFSI⁻ at super‐concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron‐induced reduction was revealed to be concentration‐dependent interfacial chemistry that only occurs among closely contact ion‐pairs, which constitutes the rationale behind the “water‐in‐salt” concept.

Super‐concentrated “water‐in‐salt” electrolytes recently spurred resurgent interest for high energy density aqueous lithium‐ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Herein we investigated LiTFSI/H₂O electrolyte interfacial decomposition pathways in the “water‐in‐salt” and “salt‐in‐water” regimes using synchrotron X‐rays, which produce electrons at the solid/electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X‐ray diffraction. We observed the surface‐reduction of TFSI⁻ at super‐concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron‐induced reduction was revealed to be concentration‐dependent interfacial chemistry that only occurs among closely contact ion‐pairs, which constitutes the rationale behind the “water‐in‐salt” concept.

Mixtures of ionic liquids (ILs) containing single-walled carbon nanotubes (SWCNTs) were prepared and characterized to obtain electrolytes with optimized transport properties for use in energy storage devices such as supercapacitors. Imidazolium ILs bearing cations with side chains of different functionality, coupled with bis(trifluoromethylsulfonyl)amide (NTf₂ ^-) or bis(fluorosulfonyl)amide (FSA^-) anions, were used in mixtures containing up to 5 wt% SWCNTs. At and above 2 wt% nanotube loading, the mixtures exhibited higher conductivities than the pure ILs, in spite of the extremely high viscosities. Loadings of 5 wt% produced very high conductivities, and studies of the temperature dependence indicated a change in the charge transport mechanism between 2 and 5 wt% loading. At 5 wt% loading, the highest conductivities (up to 540 mS/cm at 25°C) were obtained for the ILs containing the NTf₂ ^- anion. These results can significantly contribute to the development of improved energy storage devices.

To facilitate the development of molten salt reactor technologies, a fundamental understanding of the physical and chemical properties of molten salts under the combined conditions of high temperature and intense radiation fields is necessary. Optical spectroscopic (UV–Vis–near IR) and electrochemical techniques are powerful analytical tools to probe molecular structure, speciation, thermodynamics, and kinetics of solution dynamics. Here, we report the design and fabrication of three custom-made apparatus: (i) a multi-port spectroelectrochemical furnace equipped with optical spectroscopic and electrochemical instrumentation, (ii) a high-temperature cell holder for time-resolved optical detection of radiolytic transients in molten salts, and (iii) a miniaturized spectroscopy furnace for the investigation of steady-state electron beam effects on molten salt speciation and composition by optical spectroscopy. Initial results obtained with the spectroelectrochemical furnace (i) and high-temperature cell holder (ii) are reported.

A versatile, compact heater designed at National Synchrotron Light Source-II forin situX-ray nano-imaging in a full-field transmission X-ray microscope is presented. Heater design for nano-imaging is challenging, combining tight spatial constraints with stringent design requirements for the temperature range and stability. Finite-element modeling and analytical calculations were used to determine the heater design parameters. Performance tests demonstrated reliable and stable performance, including maintaining the exterior casing close to room temperature while the heater is operating at above 1100°C, a homogenous heating zone and small temperature fluctuations. Two scientific experiments are presented to demonstrate the heater capabilities: (i)in situ3D nano-tomography including a study of metal dealloying in a liquid molten salt extreme environment, and (ii) a study of pore formation in icosahedral quasicrystals. The progression of structural changes in both studies were clearly resolved in 3D, showing that the new heater enables powerful capabilities to directly visualize and quantify 3D morphological evolution of materials under real conditions by X-ray nano-imaging at elevated temperature during synthesis, fabrication and operation processes. This heater design concept can be applied to other applications where a precise, compact heater design is required.

A versatile, compact heater designed at National Synchrotron Light Source-II forin situX-ray nano-imaging in a full-field transmission X-ray microscope is presented. Heater design for nano-imaging is challenging, combining tight spatial constraints with stringent design requirements for the temperature range and stability. Finite-element modeling and analytical calculations were used to determine the heater design parameters. Performance tests demonstrated reliable and stable performance, including maintaining the exterior casing close to room temperature while the heater is operating at above 1100°C, a homogenous heating zone and small temperature fluctuations. Two scientific experiments are presented to demonstrate the heater capabilities: (i)in situ3D nano-tomography including a study of metal dealloying in a liquid molten salt extreme environment, and (ii) a study of pore formation in icosahedral quasicrystals. The progression of structural changes in both studies were clearly resolved in 3D, showing that the new heater enables powerful capabilities to directly visualize and quantify 3D morphological evolution of materials under real conditions by X-ray nano-imaging at elevated temperature during synthesis, fabrication and operation processes. This heater design concept can be applied to other applications where a precise, compact heater design is required.

Ionic liquids (ILs) with relatively low viscosities and broad windows of electrochemical stability are often constructed by pairing asymmetric cations with bisfluorosulfonylimide (FSI−) or bistriflimide (NTf2 −) anions. In this work, we systematically studied the structures of ILs with these anions and related perfluorobis-sulfonylimide anions with asymmetry and/or longer chains: (fluorosulfonyl)(trifluoromethylsulfonyl)imide (BSI0,1−), bis(pentafluoroethylsulfonyl)imide (BETI−), and (trifluoromethylsulfonyl) (nonafluorobutylsulfonyl)imide (BSI1,4−) using high energy X-ray scattering and molecular dynamics simulation methods. 1-alkyl-3-methylimidazolium cations with shorter (ethyl, Im2,1+) and longer (octyl, Im1,8+) hydrocarbon chains were selected to examine how the sizes of nonpolar hydrocarbon and fluorous chains affect IL structures and properties. In comparison with these, we also computationally explored the structure of ionic liquids with anions having longer fluorinated tails.

In this study, we investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3–200 cm−1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf2]– salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr]+, 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm]+, N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr]+, 1-benzyl-3-methylimidazolium [BzMIm]+, and N-benzylpyridinium [BzPy]+ cations. The aim of this study is to better understand the effects of aromaticity in the cations’ constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but the temperature-dependent spectrum of [CHxmMPyrr][NTf2] is different from that of other ILs. While [CHxmMPyrr][NTf2] shows spectral changes with temperature in the low-frequency region below 50 cm−1, the other ILs also show spectral changes in the high-frequency region above 80 cm−1 (above 50 cm−1 in the case of [BzMPyrr][NTf2]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.

Charge transport at the interface of electrodes and ionic liquids is critical for the use of the latter as electrolytes. A room‐temperature ionic liquid, 1‐ethyl‐2,3‐dimethylimidazolium bis(trifluoromethanesulfonyl)imide (EMMIM TFSI), is investigated in situ under applied bias voltage with a novel method using low‐energy electron and photoemission electron microscopy. Changes in photoelectron yield as a function of bias applied to electrodes provide a direct measure of the dynamics of ion reconfiguration and electrostatic responses of the EMMIM TFSI. Long‐range and correlated ionic reconfigurations that occur near the electrodes are found to be a function of temperature and thickness, which, in turn, relate to ionic mobility and different configurations for out‐of‐plane ordering near the electrode interfaces, with a critical transition in ion mobility for films thicker than three monolayers.

Ionizing radiation poses a significant challenge to the operation and reliability of conventional silicon-based devices. Here, we report the effects of gamma radiation on graphene field-effect transistors (GFETs), along with a method to mitigate those effects by developing a radiation-hardened version of our back-gated GFETs. We demonstrate that activated atmospheric oxygen from the gamma ray interaction with air damages the semiconductor device, and damage to the substrate contributes additional threshold voltage instability. Our radiation-hardened devices, which have protection against these two effects, exhibit minimal performance degradation, improved stability, and significantly reduced hysteresis after prolonged gamma radiation exposure. We believe this work provides an insight into graphene's interactions with ionizing radiation that could enable future graphene-based electronic devices to be used for space, military, and other radiation-sensitive applications.

In order to explore the effect of multiple ether functionalities on ionic liquid properties, a series of ten pyrrolidinium ionic liquids and ten imidazolium ionic liquids bearing ether and alkyl side chains of varying lengths (4 to 10 atoms in length) were prepared. Their physical properties, such as viscosity, conductivity and thermal profile were measured and compared. Consistent with earlier literature, a single ether substituent substantially decreases the viscosity of pyrrolidinium and imidazolium ILs compared to their alkyl congeners. Remarkably, as the number of ether units in the pyrrolidinium ILs increases there is hardly any increase in the viscosity, in contrast to alkylpyrrolidinium ILs where the viscosity increases steadily with chain length. Viscosities of imidazolium ether ILs increase with chain length but always remain well below their alkyl congeners. These results provide significant insight on the choice of starting materials for researchers designing ILs for specific applications.

We report here on the transport properties of ionic liquid mixtures that incorporate a series of asymmetrical dications, including heterodications. The dicationic ILs combine either triphenylphosphonium and trimethylammonium cationic sites that are bridged to methylimidazolium or methylpyrrolidinium cationic sites. Mixtures were made of the dicationic bis(trifluoromethylsulfonyl)amide ionic liquids with N-ethoxyethyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. The IL mixtures were characterized for their transport properties (temperature dependent conductivity and viscosity) and thermal properties (melting point and glass transition point).

Binary mixtures of ionic liquids (ILs) were prepared and characterized to obtain ILs with viscosity and conductivity properties optimized for use in energy storage devices such as supercapacitors. The bis(trifluoromethylsulfonyl)amide anion (NTf₂ ^-) was the common anion for both ILs in the mixture. Ethoxyethyl was the common substituent on the solute and solvent, as ether substituents have been shown to produce low viscosity ILs. N-Ethoxyethyl-N-methylpyrrolidinium NTf₂ was used as the solvent for all of the IL mixtures. The solutes were either monocationic or dicationic and made up 10% of the binary mixture by weight. We report here on the physical properties of the individual ILs and their binary mixtures.

Ionic liquids (ILs) incorporating cyclic phosphonium cations are a novel category of materials. We report here on the synthesis and characterization of four new cyclic phosphonium bis(trifluoromethylsulfonyl)amide ILs with aliphatic and aromatic pendant groups. In addition to the syntheses of these novel materials, we report on a comparison of their properties with their ammonium congeners. These exemplars are slightly less conductive and have slightly smaller self-diffusion coefficients than their cyclic ammonium congeners.

Ionic liquids are subjects of intense current interest within the physical chemistry community. A great deal of progress has been made in just the past five years toward identifying the factors that cause these salts to have low melting points and other useful properties. Supramolecular structure and organization have emerged as important and complicated topics that may be key to understanding how chemical reactions and other processes are affected by ionic liquids. New questions are posed, and an active debate is ongoing regarding the nature of nanoscale ordering in ionic liquids. The topic of reactivity in ionic liquids is still relatively unexplored; however, the results that have been obtained indicate that distributed kinetics and dynamical heterogeneity may sometimes, but not always, be influencing factors.

Pulse radiolysis, utilizing short pulses of high-energy electrons from accelerators, is a powerful method for rapidly generating reduced or oxidized species and other free radicals in solution. Combined with fast time-resolved spectroscopic detection (typically in the ultraviolet/visible/near-infrared), it is invaluable for monitoring the reactivity of species subjected to radiolysis on timescales ranging from picoseconds to seconds. However, it is often difficult to identify the transient intermediates definitively due to a lack of structural information in the spectral bands. Time-resolved vibrational spectroscopy offers the structural specificity necessary for mechanistic investigations but has received only limited application in pulse radiolysis experiments. For example, time-resolved infrared (TRIR) spectroscopy has only been applied to a handful of gas-phase studies, limited mainly by several technical challenges. We have exploited recent developments in commercial external-cavity quantum cascade laser (EC-QCL) technology to construct a nanosecond TRIR apparatus that has allowed, for the first time, TRIR spectra to be recorded following pulse radiolysis of condensed-phase samples. Near single-shot sensitivity of ΔOD <1 × 10⁻³ has been achieved, with a response time of <20 ns. Using two continuous-wave EC-QCLs, the current apparatus covers a probe region from 1890–2084 cm⁻¹, and TRIR spectra are acquired on a point-by-point basis by recording transient absorption decay traces at specific IR wavelengths and combining these to generate spectral time slices. The utility of the apparatus has been demonstrated by monitoring the formation and decay of the one-electron reduced form of the CO2 reduction catalyst, [Reⁱ(bpy)(CO)₃(CH₃CN)]⁺, in acetonitrile with nanosecond time resolution following pulse radiolysis. Characteristic red-shifting of the ν(CO) IR bands confirmed that one-electron reduction of the complex took place. The availability of TRIR detection with high sensitivity opens up a wide range of mechanistic pulse radiolysis investigations that were previously difficult or impossible to perform with transient UV/visible detection.

A few classes of ionic liquids were synthesized and investigated for their physical properties as a function of structural variation. Bis(oxalato)borate (BOB) and bis(trifluoromethylsulfonyl)imide (NTf2) ionic liquids (ILs) containing pyridinium, 4-dimethylaminopyridinium (DMAP) and pyrrolidinium cations bearing alkyl, benzyl, hydroxyalkyl and alkoxy substituents, were prepared from the corresponding halide salts. The physical properties of the DMAP based ionic liquids including viscosity, conductivity and thermal profiles were compared to those of their unsubstituted pyridinium analogues. The properties of the BOB and NTf2 salts bearing similar cations were also compared. It was found that the DMAP salts were easier to synthesize and purify and have higher thermal decomposition points compared to their pyridinium and pyrrolidinium analogues. The BOB salts were found to be higher melting and more viscous than the NTf2 salts. The synthesis and physical properties of the various ILs will be discussed.

Ionic liquids are an emerging class of materials with a diverse and extraordinary set of properties. Understanding the origins of these properties and how they can be controlled by design to serve valuable practical applications presents a wide array of challenges and opportunities to the chemical physics and physical chemistry community. We highlight here some of the significant progress already made and future research directions in this exciting area.

The kinetic salt effect on the disproportionation reaction between diiodide anions in methanol has been examined using two ionic liquids and one inorganic salt. The ionic reaction was accelerated significantly, depending on the cation of the salt, and the ionic liquids enhanced the reaction more effectively. At higher concentrations the reaction rates decrease owing to increasing viscosities.

Laser flash photolysis is applied to study the recombination reaction of lophyl radicals in ionic liquids in comparison with dimethylsulfoxide as an example of a traditional organic solvent. The latter exhibits a similar micropolarity as the ionic liquids. The ionic liquids investigated are 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (1), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate (2), and 1‐butyl‐3‐methylimidazolium tetafluoroborate (3). The recombination of the photolytic generated lophyl radicals occur significantly faster in the ionic liquids than expected from their macroscopic viscosities and is a specific effect of these ionic liquids. On the other hand, this reaction can be compared with the macroscopic viscosity in the case of dimethylsulfoxide. Activation parameters obtained for lophyl radical recombination suggest different, anion‐dependent mechanistic effects. Quantum chemical calculations based on density functional theory provide a deeper insight of the molecular properties of the lophyl radical and its precursor. Thus, excitation energies, spin densities, molar volumes, and partial charges are calculated. Calculations show a spread of spin density over the three carbon atoms of the imidazolyl moiety, while only low spin density is calculated for the nitrogens.

Herein we report a new class of low‐melting ionic liquids (IL) that consist of N,N,N‐trialkylammonioundecahydrododecaborates(1−) as the anion and a range of cations. The cations include the common cations of conventional ILs such as tetraalkylammonium, N‐alkylpyridinium, and N‐methyl‐N′‐alkylimidazolium. In addition, their salts with lithium, potassium, and proton cations also exist as ILs. Pulse radiolysis studies indicate that the anions do not react with solvated electrons.

We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P14+∕NTf2−), N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P1EOE+∕NTf2−), N-ethoxyethyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P1EOE+∕NTf2−), N-ethoxyethyl-N-methylpyrrolidinium bromideP1EOE+, and N-ethoxyethyl-N-methylpyrrolidinium dicyanoamide P1EOE+∕DCA−). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P14+, P1EOM+, and P1EOE+ paired with the NTf2− anion. The other group of liquids consists of the P1EOE+ cation paired with each of the three anions NTf2−,Br−, and DCA−. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (∼2ps) and intermediate (∼20ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750cm−1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2− anion. The intermolecular vibrational line shapes between 0 and 150cm−1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape.

The BNL Laser-Electron Accelerator Facility (LEAF) uses a laser-pulsed photocathode, radio-frequency electron gun to generate ⩾7 ps pulses of 8.7 MeV electrons for pulse radiolysis experiments. The compact and operationally simple accelerator system includes synchronized laser pulses that can be used to probe or excite the electron-pulsed samples to examine the dynamics and reactivity of chemical species on the picosecond time scale.

One-electron reduction of [Ru(menbpy)3]2+ [menbpy = 4,4′-di{(1R,2S,5R)-(−)-menthoxycarbonyl}-2,2′-bipyridine] by pulse radiolysis produces a Ru(II) complex of a menbpy-centered anion radical, which reduces Δ-[Co(acac)3] more rapidly than Λ-[Co(acac)3] with an enantioselectivity of 2.7 in 85% EtOH/H2O.

Flash photolysis and pulse radiolysis measurements demonstrate a conformational dependence of electron transfer rates across a 16-mer helical bundle (three-helix metalloprotein) modified with a capping CoIII(bipyridine)3 electron acceptor at the N terminus and a 1-ethyl-1'-ethyl-4,4'- bipyridinium donor at the C terminus. For the CoIII(peptide)3-1-ethyl-1'-ethyl-4,4'-bipyridinium maquettes, the observed transfer is a first order, intramolecular process, independent of peptide concentration or laser pulse energy. In the presence of 6 M urea, the random coil bundle (approximately 0% helicity) has an observed electron transfer rate constant of kobs = 900 +/- 100 s-1. In the presence of 25% trifluoroethanol (TFE), the helicity of the peptide is 80% and the kobs increases to 2000 +/- 200 s-1. Moreover, the increase in the rate constant in TFE is consistent with the observed decrease in donor-acceptor distance in this solvent. Such bifunctional systems provide a class of molecules for testing the effects of conformation on electron transfer in proteins and peptides.

The construction of a high-pressure cell for pulse-radiolysis experiments with 2-MeV electrons at pressures up to 200 MPa using optical UV-VIS detection is described. Details on the window construction are given, and typical results for the thiocyanate test system are presented. The cell enables systematic studies of the effect of pressure on pulse radiolytically induced reactions using lower energy accelerators than previously possible.

Ionic liquids are emerging as the largest class of room‐temperature organic liquids. These ionic compounds are composed of oddly shaped organic cations and inorganic or organic anions. Ionic liquid solvents combine such properties as electric conductivity, low volatility, and a diverse range of solute–solvent interactions. In this article, we consider the recent advances in free radical chemistry occurring in this new class of organic solvents with particular emphasis on the generation and reactions of free radicals in radiolysis, photolysis, and electrochemistry of ionic liquids.