Femtosecond Pulse Radiolysis

Ultrafast pulse radiolysis with a short-pulsed electron beam and a short-pulsed analyzing light is a powerful time-resolved spectroscopic technique to study the kinetics and reactions of short-lived intermediate species or precursors in radiation chemistry and biology. In this chapter, first, we give an overview of historical developments of ultrafast pulse radiolysis. Then, we describe a femtosecond pulse radiolysis instrument, including the generation of femtosecond electron pulses by a photocathode radio frequency (rf) gun-based linear electron accelerator, the synchronization of femtosecond analyzing laser with the electron pulses, the transient absorption measurement with double-pulse technique, and the observations of the formation processes and ultrafast reactions of hydrated electrons in water. Finally, two innovative techniques, which enable to improve the time resolution in next pulse radiolysis development, are presented

Concept model of atomic hydrogen dry developing process for photolithographic patterning

Atomic hydrogen dry etching was used for microstructure fabrication. Photolithography was proposed and achieved by a dry development process using atomic hydrogen irradiation. The reaction system of poly(methyl methacrylate) mixed with molecular benzophenone was examined as a model system for a proof-of-concept study. Optical patterning was experimentally made on a thin layer of poly(methyl methacrylate) with benzophenone by UV light exposure with a photomask. The reaction system acted as a negative tone resist in the proposed process. Thus, a model system for a new atomic hydrogen dry development process was proposed and successfully demonstrated.Yuki Takemori, Masao Gohdo, Yuta Koda, and Hideo Horibe, "Concept model of atomic hydrogen dry developing process for photolithographic patterning", AIP Advances 10, 105223 (2020) https://doi.org/10.1063/5.0027509

Cyclic phosphonium ionic liquids

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

Direct ionization-driven observational approaches for radical cation formation in solution for pulse radiolysis

Radical cations’ dynamics in early stage reactions in the ionizing radiation induced reaction is essential to understanding the whole reaction scheme. The observation of radical cations in tetrahydrofuran (THF) solutions was demonstrated for time-resolved measurements using pulse radiolysis. The designedly concentrated solutions enabled the observation of the direct ionization-driven radical cations. In THF, the transient absorption spectra of the biphenyl radical cations, which were generated through direct ionization of biphenyl under electron beam irradiation, were found to be associated with the biphenyl radical anions generated by the attachment of an excess electron to the biphenyl. Furthermore, when polystyrene (PS) was used as the solute in THF solutions, transient absorption spectra of the dimer radical cations containing solvated electrons of PS were observed. The findings, therefore, indicate that the time-resolution-based limitation on the radical cation-forming process observation, which was imposed by the diffusion-limited reactions of the solvent radical cations with the solute, could be overcome by employing direct ionization in THF. This method can be employed to study the reactivity of radical cations with solvents and the stability of radical cations in fluid media

Structure of 1‑Alkyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide Ionic Liquids with Linear, Branched, and Cyclic Alkyl Groups

X-ray scattering and molecular dynamics simulations have been carried out to investigate structural differences and similarities in the condensed phase between pyrrolidinium-based ionic liquids paired with the bis­(trifluoromethylsulfonyl)­amide (NTf₂^–) anion where the cationic tail is linear, branched, or cyclic. This is important in light of the charge and polarity type alternations that have recently been shown to be present in the case of liquids with cations of moderately long linear tails. For this study, we have chosen to use the 1-alkyl-1-methylpyrrolidinium, Pyrr_1,<i>n</i>⁺ with <i>n</i> = 5 or 7, as systems with linear tails, 1-(2-ethylhexyl)-1-methylpyrrolidinium, Pyrr_1,EtHx⁺, as a system with a branched tail, and 1-(cyclohexylmethyl)-1-methylpyrrolidinium, Pyrr_1,ChxMe⁺, as a system with a cyclic tail. We put these results into context by comparing these data with recently published results for the Pyrr_1,<i>n</i>⁺/NTf₂^– ionic liquids with <i>n</i> = 4, 6, 8, and 10., General methods for interpreting the structure function <i>S</i>(<i>q</i>) in terms of <i>q</i>-dependent natural partitionings are described. This allows for an in-depth analysis of the scattering data based on molecular dynamics (MD) trajectories that highlight the effect of modifying the cationic tail