Computational analysis of the spatial distributions of low-energy electrons generated via water photolysis and photoinjection into electrodes in water

Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tsuchida, Hidetsugu*; Yokoya, Akinari*

Journal of Chemical Physics, 162(15), p.154102_1 - 154102_11, 2025/04

https://doi.org/10.1063/5.0252783

Scientific knowledge of low-energy electrons resulting from water radiolysis is required to estimate radiation DNA damage. However, since the analysis of water radiolysis is very complex, this study focuses on the experimental values of low-energy electrons related to simple water photolysis and those generated by photoirradiation of electrodes in water. Both experimental analyses involve the presence or absence of a Coulomb field in the parent ion. In this study, we analyzed these experimental values using a calculation code that combines Monte Carlo and molecular dynamics methods. As a result, it was shown that the code reproduced the experimental values even under different experimental conditions, and the code was validated. The calculation code will be a powerful tool for analyzing the interaction between low-energy electrons and DNA, and is expected to be applied to elucidate the formation mechanism of radiation DNA damage.

Pressure-induced polymerization of 1,4-difluorobenzene towards fluorinated diamond nanothreads

Che, G.*; Fei, Y.*; Tang, X.*; Zhao, Z.*; Hattori, Takanori; Abe, Jun*; Wang, X.*; Ju, J.*; Dong, X.*; Wang, Y.*; et al.

Physical Chemistry Chemical Physics, 27(2), p.1112 - 1118, 2025/01

https://doi.org/10.1039/D4CP03751K

Pressure-induced polymerization (PIP) of aromatic molecules has emerged as an effective method for synthesizing various carbon-based materials. In this work, PIP of 1,4-difluorobenzene (1,4-DFB) was investigated. high-pressure investigations of 1,4-DFB reveal a phase transition at approximately 12.0 GPa and an irreversible chemical reaction at 18.7 GPa. Structural analysis of the product and the kinetics of the reaction uncovered the formation of pseudohexagonal stacked fluoro-diamond nanothreads with linear growth. Compared to the crystal structures of benzene under high pressure, 1,4-DFB exhibits higher compression along the [001] axis. The anisotropic compression is attributed to the stronger H interaction along the [01] axis and the potential compression-inhibiting HF interactions along the [100] and [010] axes, and it facilitates a possible reaction pathway along the [01] axis. This work emphasizes the crucial role of functionalization in modulating molecular stacking and influencing the reaction pathway.

Self-learning path integral hybrid Monte Carlo with mixed and machine learning potentials for modeling nuclear quantum effects in water

Thomsen, B.; Nagai, Yuki*; Kobayashi, Keita; Hamada, Ikutaro*; Shiga, Motoyuki

Journal of Chemical Physics, 161(20), p.204109_1 - 204109_18, 2024/11

https://doi.org/10.1063/5.0230464

We introduce the self-learning path integral hybrid Monte Carlo with mixed and machine learning potentials (SL-PIHMC-MIX) method which allows the application of hybrid Monte Carlo for both path integrals and for larger system sizes. The method shows savings of an order of magnitude with respect to the number of DFT calculations needed to calculate and converge the structure of room temperature water when using SL-PIHMC-MIX over ab initio path integral molecular dynamics (PIMD).

Liquid water radiolysis induced by secondary electrons generated from MeV-energy carbon ions

Tsuchida, Hidetsugu*; Tezuka, Tomoya*; Kai, Takeshi; Matsuya, Yusuke*; Majima, Takuya*; Saito, Manabu*

Journal of Chemical Physics, 161(10), p.104503_1 - 104503_8, 2024/09

https://doi.org/10.1063/5.0227465

Although fast ion beams can damage DNA by chemical products such as secondary electrons produced by their interaction with water in living cells, the process of formation of these chemical products in the Bragg peak region used in particle therapy is not fully understood. To investigate this process, we performed experiments to evaluate the yields of radiolytic products produced when a liquid water jet in vacuum is irradiated with a MeV-energy carbon beam. In addition, ionization processes in water due to incident ions and secondary electrons were simulated using a radiation transport Monte Carlo code. The results indicated that the primary source of ionization in water is secondary electrons. Finally, we show that these elementary processes contribute to the development of radiation biophysics and biochemistry to study the formation mechanism of DNA damage.

Consideration of the dielectric response for radiation chemistry simulations

Toigawa, Tomohiro; Kai, Takeshi; Kumagai, Yuta; Yokoya, Akinari*

Journal of Chemical Physics, 160(21), p.214119_1 - 214119_9, 2024/06

https://doi.org/10.1063/5.0211089

The spur reaction is crucial for determining radiolysis or photolysis in liquid, but the spur expansion process has yet to be elucidated. One reason is the need to understand the role of the dielectric response of the solvating molecules surrounding the charged species generated by ionization. The dielectric response corresponds to the time evolution of the permittivity and might affect the chemical reaction-diffusion of the species in a spur expansion process. This study examined the competitive relationship between reaction-diffusion kinetics and the dielectric response by solving the Debye-Smoluchowski equation while considering the dielectric response. The Coulomb force between the charged species gradually decreases with the dielectric response. Our calculation results found a condition where fast recombination occurs before the dielectric response is complete. Although it has been reported that the primary G-values of free electrons depend on the static dielectric constant under low-linear-energy transfer radiation-induced ionization, we propose that considering the dielectric response can provide a deeper insight into fast recombination reactions under high-linear-energy transfer radiation- or photo-induced ionization. Our simulation method enables the understanding of fast radiation-induced phenomena in liquids.

Coverage-dependent desorption kinetics of water on a well-ordered alumina thin film surface

Koshida, Hiroyuki*; Wilde, M.*; Fukutani, Katsuyuki

Journal of Chemical Physics, 160(3), p.034703_1 - 034703_9, 2024/01

https://doi.org/10.1063/5.0183443

Incorporation of a bromine atom into DNA-related molecules changes their electronic properties

Hirato, Misaki*; Yokoya, Akinari*; Baba, Yuji*; Mori, Seiji*; Fujii, Kentaro*; Wada, Shinichi*; Izumi, Yudai*; Haga, Yoshinori

Physical Chemistry Chemical Physics, 25(21), p.14836 - 14847, 2023/05

https://doi.org/10.1039/D3CP01597A

Nature of the physicochemical process in water photolysis uncovered by a computer simulation

Kai, Takeshi; Toigawa, Tomohiro; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yokoya, Akinari*

Journal of Chemical Physics, 158(16), p.164103_1 - 164103_8, 2023/04

https://doi.org/10.1063/5.0149333

New insight into water radiolysis and photolysis is indispensable in the dramatic progress of sciences and technologies in various research areas. In the radiation field, reactive hydrated electrons are considerably produced along radiation tracks. Although the formation results from a transient dynamic correlation between ejected electrons and water, the individual mechanisms of electron thermalization, delocalization, and polarization are unknown. Using a dynamic Monte Carlo code, we show herein that the ejected electrons are immediately delocalized by molecular excitations in parallel with phonon polarization and gradually thermalized by momentum transfer with an orientation polarization in a simultaneous manner. Our results show that these mechanisms heavily depend on the intermolecular vibration and rotation modes peculiar to water. We expect our approach to be a powerful technique for connecting physical and chemical processes in various solvents.

Laser-fluence dependence of resonance-enhanced multiphoton reduction of trivalent europium

Matsuda, Shohei; Nakashima, Nobuaki*; Yokoyama, Keiichi; Taniguchi, Seiji*; Chosrowjan, H.*; Somekawa, Toshihiro*; Yatsuhashi, Tomoyuki*

Chemical Physics Letters, 802, p.139759_1 - 139759_6, 2022/09

https://doi.org/10.1016/j.cplett.2022.139759

no abstracts in English

Temperature dependence of positron annihilation lifetime in near-surface and bulk of room-temperature ionic liquid observed by a slow positron beam

Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*

Chemical Physics Letters, 795, p.139507_1 - 139507_4, 2022/05

https://doi.org/10.1016/j.cplett.2022.139507

We obtained the temperature dependence up to 150C of the triplet positronium (-Ps) lifetime in N,N,N-Trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by the vertical slow positron beamline installed at AIST. Positrons penetrate into the liquid surface of TMPA-TFSI with the positron energies of 2 keV and 12 keV to investigate at the near-surface and the balk. The surface structure was visible at 150C, 120C above the melting temperature. The -Ps lifetime became shorter at higher temperatures for both positron energies. Similar temperature dependence had appeared just in water as the result of the reaction of -Ps and radiolysis products such as the OH radicals. The temperature dependence observed for TMPA-TFSI suggested that the chemical reaction of -Ps occurred.