Electron Beam Pulse Radiolysis Research Articles

Formation of intramolecular dimer radical ions of diphenyl sulfones

Dimer radical ions of aromatic molecules in which excess charge is localized in a pair of rings have been extensively investigated. While dimer radical cations of aromatics have been previously produced in the condensed phase, the number of molecules that form dimer anions is very limited. In this study, we report the formation of intramolecular dimer radical ions (cations and anions) of diphenyl sulfone derivatives (DPs) by electron beam pulse radiolysis in the liquid phase at room temperature. The density functional theory (DFT) calculations also showed the formation of the dimer radical ions. The torsion barrier of the phenyl ring of DPs was also calculated. It was found that the dimer radical ions show the larger barrier than the neutral state. Finally, stability of the dimer radical anion is dependent on not only the inductive effect of the sulfonyl group but the conjugation involving the d-orbital of the S atom and the phenyl rings.

Study of Interrelation Between Reaction of Polymer-Bound/Blend Photoacid Generator with Solvated Electron and Acid Generation Efficiency

Polymer-bound photoacid generators (PAGs) (anion bound) and their corresponding polymers were synthesized for evaluation of the reactivity of polymer-bound PAGs with secondary electrons in solutions by the electron beam pulse radiolysis method. In the solutions, the rate constants of polymer-bound PAGs are much lower than those of polymer-blend PAGs. In addition, we evaluated the acid generation efficiencies of polymer-bound PAGs. As a result, despite the film state, the acid generation efficiency of polymer-bound PAGs are about 10% lower than those of the polymer-blend PAGs. These differences are explained by the difference in stabilization effects between polymer-bound PAGs and polymer-blend PAGs in both solutions and films.

Geminate Charge Recombination in Liquid Alkane with Concentrated CCl4: Effects of CCl4 Radical Anion and Narrowing of Initial Distribution of Cl–

Dynamics of radical cations and electrons in an admixture of a linear saturated hydrocarbon (n-dodecane) and halocarbon (carbon tetrachloride, CCl(4)) were investigated by picosecond electron beam pulse radiolysis. The decay of thermalized electrons (e(th)(-)) observed in infrared transient photoabsorption were simply accelerated by the addition of CCl(4), giving a high rate constant of 2.3 × 10(11) mol(-1) dm(3) s(-1). The decrease of the initial yield of e(th)(-) was quantified by C(37) (50 mmol), which is linked to the reaction of epithermal electrons (e(-)) with CCl(4). In contrast, the n-dodecane radical cation (RH(2)(•+)) monitored in the near-infrared indicated a convex-type dependence of the decay rate on CCl(4) concentration, although the initial yield of RH(2)(•+) remained almost constant up to a much higher CCl(4) concentration. The decay of RH(2)(•+) was analyzed by Monte Carlo simulations of geminate ion recombination with e(th)(-), chlorine anion (Cl(-)) formed via dissociative electron attachment, and CCl(4) radical anion. The results showed a good agreement with the experiments by considering two assumptions: (1) CCl(4) radical anion formed via e(th)(-) attachment and (2) narrowing of the initial distribution of Cl(-). The decrease in the initial yield of RH(2)(•+) at high CCl(4) concentration was well explained by immediate decomposition of CCl(4)(•+) to CCl(3)(+) and hole transfer from CCl(4)(•+) to adjacent RH(2) without diffusive motion of the reactants. Time-dependent density functional theory supported the spectroscopic assignment of intermediate species in the n-dodecane/CCl(4) system. The present results would be of help in understanding the electron capture reaction in multicomponent systems such as a chemically amplified resist in lithography.

Electron beam induced grafting of N-isopropylacrylamide to a poly(ethylene-terephthalate) membrane for rapid cell sheet detachment

Intact sheets of human prostate epithelium cells were successfully detached from a poly(N-isopropylacrylamide) (pNIPAM) membrane radiolytically grafted to poly(ethlylene-terephthalate (PET) culture dishes. The detachment process took less than 20 min without damaging the sheet structure. The grafting was performed using a high-energy electron beam to covalently bond NIPAM to the surface of PET culture dishes. This work demonstrates that the optimal conditions for uniform grafting can be achieved by adding argon-saturated solutions of NIPAM monomer onto pre-irradiated, surface-activated PET membranes. The solutions and the membranes were then irradiated under anaerobic conditions to a total absorbed dose of 25 kGy. This grafting method involves producing carbon-centered free radicals NIPAM and PET from both NIPAM and PET, respectively. An investigation of the kinetics of the early stages of polymerization of NIPAM was performed through electron beam pulse radiolysis with optical detection. The pulse radiolysis experiments of anaerobic NIPAM methanol solutions show that the e sol − reacts very rapidly with NIPAM producing NIPAM − anions with a reaction rate constant of 1.4×10 9±10% L mol −1 s −1. The NIPAM − anions then undergo a protonation reaction producing the initiation free radical (NIPAM ) with a reaction rate constant of 9×10 2 L mol −1 s −1. Along with pulse radiolysis, electron paramagnetic resonance (EPR) measurements show that the radiolytically produced carbon-centered free radicals of the PET, PET , decay following an overall observed pseudo-first-order reaction with rate constants of k=2.0×10 −4 and 7.0×10 −4 s −1 produced in argon and in air, respectively. The overall observed decay reaction involve PET +PET cross-linking, PET +O 2, PET + HO 2 , and PET+H-atoms, since these EPR measurements were conducted under aerobic conditions.

Refractive Index Control and Electron Beam Pulse Radiolysis of Transparent Polyimides

Refractive index change was induced by electron beam irradiation to transparent polyimides as large as 10-2. Active intermediates during the electron beam irradiation were determined by electron beam pulse radiolysis of several model imide compounds. Strong electron affinity of the transparent polyimides was one of the key factors for the reaction.

Synthesis of Allene Derivatives and their Photophysical Processes

Allenes, one of the compounds with cumulative double bonds, are attracting much interests due to the characteristics of their twisted π-conjugated bonds. Several allenes were synthesized to characterize their electronic features by their ground-state absorption, transient absorption and emission spectra to be found that they increase conjugation length in the excited state due to their conformational change. Photophysical process and active species were determined by laser flash photolysis and electron beam pulse radiolysis to find that intramolecular charge transfer of an allene is induced upon electron beam irradiation.

Transient absorption spectroscopy of radical ions of rigid anti- and syn-tetrasilane

Transient absorption spectra of ion radicals were observed for tetrasilanes with rigid syn or anti Si units by electron beam pulse radiolysis. Two transient absorption bands at 4.1 and 2.8 eV were clearly resolved for the anion radical of syn-tetrasilane, while for anti-tetrasilane, the anion radical produced a broad absorption band at 4.4 eV. Cation radicals of the tetrasilanes gave similar optical transitions at 3.6 and 2.1 eV for the syn form, and 3.8 eV for the anti form. The spectra for the ion radicals of anti-tetrasilane are identical to those of ion radicals of permethylated pentasilanes or hexasilanes, suggesting that the ion radicals of oligosilane without configurational constraint take an anti conformation. The unique spectra of ion radicals of syn-tetrasilane reflect the large gap between the second and third HOMO (LUMO) of neutral molecules, which is also induced by the configurational constraint.

Revealing the Nature of Trapping Sites in Nanocrystalline Titanium Dioxide by Selective Surface Modification

Excess electrons in nanocrystalline TiO2 were studied in bare and dopamine-capped TiO2 nanoparticles by electron-beam pulse radiolysis. Reaction of hydrated electrons with dopamine-capped TiO2 nanoparticles was found to be at the diffusion-controlled limit, k = 1 × 1011 M-1 s-1, while the reaction with 1-hydroxy-1-methylethyl radicals, (CH3)2ĊOH, was 2 orders of magnitude slower, k = 4 × 108 M-1 s-1. The reactions result in injection of electrons into the conduction band of TiO2 nanoparticles. Optical absorption spectra of injected excess electrons in dopamine-capped nanoparticles display monotonic featureless wavelength dependence up to 1800 nm. In contrast, bare particles have shown two preferential optical transitions with energies in the visible region (λmax = 670 nm and λmax = 900 nm). Flat band potential of dopamine-capped TiO2 nanoparticles was shifted by 100 mV to more negative values. The strong coupling of dopamine to surface Ti atoms was also found to improve the separation of photogenerated charges. This was demonstrated by the enhanced efficiency of photogenerated electrons in reducing silver cations to metallic silver in systems linked via a dopamine bridge, compared to the same systems linked through carboxyl groups.

Dynamics of Charge Carriers on Poly[bis(p-alkylphenyl)silane]s by Electron Beam Pulse Radiolysis

The degree of electron delocalization along polymer skeletons was discussed for ion radicals of poly[bis(p-alkylphenyl)silane]s by electron beam pulse radiolysis. The degree of delocalization of ne...

Radiolysis of aqueous solutions with pulsed helium ion beams—2. Yield of SO4− formed by scavenging hydrated electron as a function of S2O2−8 concentration

Yields of SO4− in the radiolysis of aqueous (NH4)2S2O8 solutions with pulsed 24 MeV 4He2+ ion beams were measured in the concentration range from 1×10−4 to 1 mol dm−3. The yield increased with increasing the concentration, and it was smaller than that in electron beam pulse radiolysis in the concentration range measured. The results were compared with the reported Ge−aq derived from various scavengers. Though the yields agree well for low LET radiations, the result of the present research for 4He ion beams is smaller than the yield determined by a product analysis method. This suggests that once formed SO4− disappears by the intra-track reactions and that this effect is more important in ion beam radiolysis because of more dense production of the initial species. Simulation by the deterministic diffusion kinetic model supports it qualitatively.

Time-resolved spectroscopy of solid poly(1-vinyl naphthalene)following electron beam pulse radiolysis: pulse radiolytic studies on polymers

Transient emission studies following pulse radiolysis of solid poly(1-vinyl naphthalene) show existence of excited monomers and two excimers. Quenching experiments indicate that excimers are not formed directly by recombination of ions but probably by trapping of migrating monomeric excitation in performed traps whose density is approximately one in 10 3.

Nanosecond time-resolved EPR spectroscopy: time profiles via integration of free induction decays

Tune dependence of transient magnetization can be sampled by using a single microwave pulse and observing the intensity of free induction decay (FID). The FID method is illustrated and compared to the two-pulse electron spin echo (ESE) technique. The time pronies of the hydrogen atoms created by electron beam pulse radiolysis or acidic water are used to illustrate the advantages of the FID method. Superior signal to noise and better effective response time of the F ID method makes it an ideal tool for the study of fast reacting radicals in liquids.

Pulse-Radiolysis Study of the Formation of Benzyl Radicals from Benzyl Chloride in Cyclohexane in the Gas Phase

The yield of benzyl radical (Bz) formed by electron-beam pulse radiolysis of benzyl chloride (BzCl) in cyclohexane vapor (1.3 atm/120°) has been studied by optical absorption measurements. Electron scavengers lower the benzyl radical (Bz) absorption by competing with dissociative electron capture by BzCl. A study of this competition gave the relative rate constants for electron capture at 120°C (SF6 = 1) : BzCl = 1.6 × 10−3, CCl4 = 0.3, CH3Br = 5 × 10−5, C6H5NO2 ∼ 2 × 10−2. The maximum depression of the absorption, Δ(Bz)max, which was independent of the electron scavenger used and of the BzCl concentration (0.2 to at least 4 mole %), is believed to correspond to the yield of Bz from dissociative capture. With benzyl bromide, acetate, and formate in cyclohexane, Δ(Bz)max was the same as with benzyl chloride. Bz is also formed by processes other than dissociative capture which are not influenced by electron scavengers. The yield from these processes increases with increasing BzCl concentration. Using electron beam radiolysis, the decomposition of BzCl due to dissociative capture, measured by chemical analysis, G(− BzCl)e = 2.6 ± 0.4 molecules per 100 eV. 60Co γ-radiolysis gave G(− BzCl)e = 4.3 ± 0.1, which is close to the value expected if all of the electrons react by dissociative capture. Possible reasons for the low value with electron radiolysis are discussed.