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scattering length from 
photoproduction on the proton near the reaction thresholdIshikawa, Takatsugu*; Fujimura, Hisako*; Fukasawa, Hiroshi*; Hashimoto, Ryo*; He, Q.*; Honda, Yuki*; Hosaka, Atsushi; Iwata, Takahiro*; Kaida, Shun*; Kasagi, Jirota*; et al.
Physical Review C, 101(5), p.052201_1 - 052201_6, 2020/05
Times Cited Count：4 Percentile：37.19(Physics, Nuclear)Itakura, Ryuji; Hosaka, Koichi*; Yokoyama, Atsushi; Ikuta, Tomoya*; Kannari, Fumihiko*; Yamanouchi, Kaoru*
Progress in Ultrafast Intense Laser Science XI; Springer Series in Chemical Physics, Vol.109, p.23 - 42, 2015/00
We investigate the multichannel dissociative ionization of ethanol in intense laser fields by the photoelectron-photoion coincidence momentum imaging and identify separately the ionization and subsequent electronic excitation in ethanol. From the energy correlation between a photoelectron and a fragment ion, we reveal the amount of the internal energy gained by ethanol cations from the laser field varies depending on the respective ionization and electronic excitation pathways.
Hosaka, Yuji*; Oyama, Tomoko; Oshima, Akihiro*; Enomoto, Satoshi*; Washio, Masakazu*; Tagawa, Seiichi*
Journal of Photopolymer Science and Technology, 26(6), p.745 - 750, 2013/12
Times Cited Count：13 Percentile：38.16(Polymer Science)ZEP520A is one of the most popular positive electron beam (EB) resists used in research and photomask fabrication owing to its excellent properties. Herein, EB-induced initial reactions of ZEP520A were investigated via pulse radiolysis (EB energy: 28 MeV, time resolution: 10 ns). Dissociative electron attachment and formation of a charge transfer complex were definitive contributing factors to the efficient degradation of ZEP520A. Furthermore, products induced by direct ionization of ZEP520A were observed in a highly concentrated ZEP520A solution in tetrahydrofuran, suggesting that initial reactions in the ZEP520A solid film that are induced only by direct ionization could be simulated via pulse radiolysis in specific solutions.
Hosaka, Koichi*; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Itakura, Ryuji
Journal of Chemical Physics, 138(20), p.204301_1 - 204301_9, 2013/05
Times Cited Count：15 Percentile：47.87(Chemistry, Physical)Dissociative ionization of ethanol (C
H
OH) induced by an intense near-infrared laser pulse are investigated using photoelectron-photoion coincidence method. It is shown that both the electronic ground state and the first electronically excited state of CHOH
are produced at the moment of photoelectron emission. From the observed correlation between the electronic states of CHOH prepared at the moment of photoelectron emission and the kinetic energy release of the fragment ions, it is revealed that CHOH prepared in the electronic ground state at the photoelectron emission gains larger internal energy in the end than that prepared in the electronically excited state. The averaged internal energy of CHOH just before the dissociation is found to increase when the laser field intensity increases from 9 to 23 TW/cm
. And when the laser pulse duration increases from 35 to 800 fs.
Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Itakura, Ryuji
Journal of Physics B; Atomic, Molecular and Optical Physics, 44(19), p.191002_1 - 191002_5, 2011/10
Times Cited Count：10 Percentile：45.81(Optics)Ionization and subsequent electronic excitation occurring within the same laser pulse (400 nm, 96 fs, 1.3
18 TW/cm
) are separately investigated by measuring in coincidence an electron and a product ion produced from CHOH. We reveal that the nascent population in the electronically excited CHOH prepared by the ionization decreases as the laser intensity increases, while the subsequent electronic excitation is enhanced through the resonant electronic transitions. Ionization and electronic excitation mechanisms are described based on the electronic state distributions of CHOH.
Hosaka, Koichi; Itakura, Ryuji; Yokoyama, Keiichi; Yamanouchi, Kaoru*; Yokoyama, Atsushi
Chemical Physics Letters, 475(1-3), p.19 - 23, 2009/06
Times Cited Count：12 Percentile：37.28(Chemistry, Physical)In intense laser fields, molecules are decomposed into fragments through a number of competing dissociative ionization pathways. We investigate the dissociative ionization dynamics of ethanol in intense laser fields with photoelectron-photoion coincidence momentum imaging. The channel-specific photoelectron spectra reveal the electronic states prepared just after ionization, depending both on the decomposition pathways and on the temporal profile of laser pulses.
Itakura, Ryuji; Hosaka, Koichi*; Yamanouchi, Kaoru*; Yokoyama, Atsushi
no journal, ,
By the photoelectron-photoion coincidence momentum imaging, channel-specific photoelectron images of ethanol and oxygen molecules ionized in intense laser fields are obtained at different laser field intensities and pulse durations for clarifying their electronic excitation mechanisms.
Itakura, Ryuji; Hosaka, Koichi*; Yamanouchi, Kaoru*; Yokoyama, Atsushi
no journal, ,
In order to clarify the mechanism of dissociative ionization of ethanol in intense laser fields, the correlation maps P(E
, E
), where E and E denote kinetic energy of an electron and a fragment ion, respectively, are obtained by photoelectron-photoion coincidence momentum imaging. The kinetic energy distribution of the ions at a specific electron kinetic energy of electrons E are reproduced by an exponential curve of exp(-E/E
), where E is a variable parameter, suggesting that the intramolecular energy redistribution proceeds efficiently in the course of the dissociation process after the ionization.
Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Yokoyama, Atsushi; Kannari, Fumihiko*
no journal, ,
When ethanol molecules are irradiated with an intense UV pulse (400 nm,100 fs, I = 10 TW/cm), channel-specific photoelectron momentum images correlated with CHOH, CH
OH, CHOH, and CH show different features, suggesting that different electronic and vibrational state distributions are prepared upon the ionization for the respective product ion channels.
Akagi, Hiroshi; Otobe, Tomohito; Itakura, Ryuji; Hosaka, Koichi*; Yamanouchi, Kaoru; Yokoyama, Atsushi
no journal, ,
In the present work, ethanol molecules are irradiated with a circularly-polarized intense laser field (I = 1.4 
10
W/cm), and the produced electron and ion are measured in coincidence. The channel-specific photoelectron spectra correlated with the C-C and C-O dissociation channels are similar to that correlated with the parent ion, showing the series of distinctive ATI peaks. These are the signature representing that the electronic ground state of parent ions is initially prepared upon the ionization, and then, the subsequent electronic excitation leading to the C-C or C-O dissociation takes place within the same laser pulse. For the linear polarization with similar laser field intensity (1.7 10 W/cm), the ATI series is also observed, but less pronounced. This means that the electronic excitation of the parent ion is more efficiently induced in the circularly polarized laser field than in the linearly polarized one.
Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*
no journal, ,
Using photoelectron-photoion coincidence technique, we identify two ionization routes of ethanol to the electronic ground state and the electronically excited state of ethanol cation in intense ultraviolet (UV) laser fields (400 nm, 96 fs). The population ratio of the electronically excited state with respect to the electronic ground state of CHOH at the instant of the ionization decreases significantly as the laser intensity increases from 1.3 to 18.1 TW/cm. It is also revealed that the probability of the subsequent electronic excitation of CHOH within the same pulse is enhanced as the laser intensity increases.
Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*
no journal, ,
Photoionization dynamics of ethanol in two-color (400 and 800 nm) intense laser fields is investigated using photoelectron-photoion coincidence spectroscopy. It is found that the fragment ion CHOH is formed dominantly through the ionization to the electronically excited state by the 400-nm pulse when a 400-nm pulse and a 800-nm pulse are temporally separated. When a 400-nm pulse is temporally overlapped with a 800-nm pulse, the ionization to the electronically excited state by the 400-nm pulse is significantly suppressed, indicating that the ionization channel to the electronically excited state is closed due to the AC stark up-shift by the 800-nm pulse.
Oyama, Tomoko*; Enomoto, Kazuyuki*; Hosaka, Yuji*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
no journal, ,
ZEP520A (1:1 copolymer of 
-chloromethacrylate and -methylstyrene, ZEON) is a main-chain scission-type positive-tone resist widely used for electron beam (EB) lithography. ZEP520A has an excellent resolution as high as 10 nm, which is almost comparable to poly(methyl methacrylate) (PMMA), but its sensitivity is about 10 times higher than that of PMMA. In this study, ZEP520A was irradiated using a 100 kV EB, and the decomposition mechanisms were analyzed by gel permeation chromatography, X-ray photoelectron spectroscopy, NMR spectroscopy, and pulse radiolysis. Chlorines were confirmed to easily dissociate as Cl
ions (dissociative electron attachment, DEA). Multiple channels could be considered for the main-chain scission, including DEA and the charge transfer complex between phenyl rings and chlorines.
Hosaka, Koichi; Itakura, Ryuji; Yokoyama, Keiichi; Yamanouchi, Kaoru*; Yokoyama, Atsushi
no journal, ,
In intense laser fields, molecules are decomposed into fragments through a number of competing dissociative ionization pathways. We investigate the dissociative ionization dynamics of ethanol in intense laser fields with photoelectron-photoion coincidence momentum imaging. The channel-specific photoelectron spectra reveal the electronic states prepared just after ionization, depending both on the decomposition pathways and on the temporal profile of laser pulses.
Akagi, Hiroshi; Itakura, Ryuji; Hosaka, Koichi*; Yamanouchi, Kaoru; Yokoyama, Atsushi
no journal, ,
When a molecule is exposed to circularly-polarized laser fields, dissociation processes following ionization proceed differently from the case of linearly polarization. In the present work, ethanol molecules are irradiated with a circularly-polarized intense laser field (I = 1.410 W/cm, 
800 nm), and the produced electron and ion are measured in coincidence. Under the present experimental conditions, Keldysh parameter 
is calculated to be 2.6, suggesting the multiphoton ionization is expected to be dominant. The relative yields of CHOH, CHOH, and CHC with respect to the parent ion are 0.36, 0.31, and 0.01, which correspond to only 0.5, 0.4, and 0.2 of those for the linear polarization with similar laser field intensity (1.710 W/cm.
Akagi, Hiroshi; Itakura, Ryuji; Hosaka, Koichi*; Otobe, Tomohito; Yamanouchi, Kaoru; Yokoyama, Atsushi
no journal, ,
When a molecule is exposed to circularly-polarized laser fields, dissociation processes following ionization proceed differently from the case of linearly polarization. In the present work, ethanol molecules are irradiated with a circularly-polarized intense laser field (I = 1.410 W/cm, 800 nm), and the produced electron and ion are measured in coincidence. The relative yields of CHOH, CHOH, and CHC with respect to the parent ion are 0.36, 0.31, and 0.01, which correspond to only 0.5, 0.4, and 0.2 of those for the linear polarization with similar laser field intensity (1.710 W/cm), showing that the polarization change from linear to circular significantly suppresses the C-H, C-C, and C-O dissociation processes.
Akagi, Hiroshi; Otobe, Tomohito; Itakura, Ryuji; Hosaka, Koichi*; Yamanouchi, Kaoru; Yokoyama, Atsushi
no journal, ,
In the present work, ethanol molecules are irradiated with a circularly polarized intense laser field [I=(1.1
0.2) 10 W/cm, 800 nm], and the produced electron and ion are measured in coincidence. The channel-specific photoelectron spectra correlated with the C-C and C-O dissociation channels show the series of distinctive above-threshold ionization (ATI) peaks, which are similar to those correlated with the parent ion production and C-H dissociation channels. These features imply that the electronic ground state of the parent ion is initially prepared at the moment of the ionization. On the other hand, for the linear polarization, the ATI series is less pronounced, and a diffuse structure become a dominant, which means that the electronically excited states of the parent ion are produced directly on the ionization. Based on the theoretical prediction, we will discuss the polarization dependence of the ionization dynamics.
Ikuta, Tomoya; Itakura, Ryuji; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Yokoyama, Atsushi
no journal, ,
When ethanol molecules are irradiated with an intense UV pulse (400 nm, 100 fs, 1533 TW/cm), channel-specific photoelectron momentum images correlated with CHOH, CHOH, CHOH, and CH show different features, suggesting that different electronic and vibrational state distributions are prepared upon the ionization for the respective product ion channels. Basically, the electronic ground state and the first electronically excited state are prepared upon the ionization, and then the subsequent interaction between the ion and the laser field takes place, leading to the respective reaction channels.
Ikuta, Tomoya; Itakura, Ryuji; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Yokoyama, Atsushi
no journal, ,
Dissociative ionization of ethanol is more efficiently induced by intense ultraviolet laser fields than by intense near-infrared laser fields. In this study, our concern are focused on the electronic excitation dynamics in dissociative ionization of ethanol in intense ultraviolet laser fields. Photoelectron-photoion coincidence measurement allows us to understand the dissociation mechanism in terms of electronic excitation.
Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*
no journal, ,
We investigate dissociative ionization of ethanol induced by intense laser fields using photoelectron-photo ion coincidence momentum imaging. Our attentions are focused on the energy correlation between an electron and a fragment ion produced from an identical ethanol molecule. We reveal that the internal energy gained from laser fields depends on the ionization and fragmentation pathways. We discuss the ionization and dissociation mechanism based on the experimental results depending on the laser characteristics.
