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植田 寛和; 福谷 克之*; 山川 紘一郎
Frontiers in Chemistry (Internet), 11, p.1258035_1 - 1258035_7, 2023/08
水素分子には、オルトとパラと呼ばれる2つの核スピン修飾がある。2つの陽子の順列に関する対称性の制約から、オルトとパラの異性体はそれぞれ回転量子数の奇数と偶数の値しかとらない。オルソからパラへの変換は凝縮系で促進され、余剰の回転エネルギーとスピン角運動量が移動する。われわれは、分子化学吸着系とマトリックス分離系における水素の高速オルソ-パラ変換に関する最近の研究をレビューし、その変換機構と回転緩和経路について議論する。
ortho-para conversion on a metal surface; Interplay between electron and phonon systems植田 寛和; 福谷 克之
Journal of Physical Chemistry Letters (Internet), 14(34), p.7591 - 7596, 2023/08
Clarifying energy transfer processes in molecular adsorption on solid surfaces is essential to understand gas-surface interaction. Unlike the vibrational-energy transfer processes, which are thought to be well understood in detail, the rotational-energy transfer process still remains unclear. Considering the interconversion between ortho and para states of H is accompanied by the nuclear spin flip and the rotational-energy transfer, the surface-temperature dependence of the ortho-to-para conversion of molecularly chemisorbed H on Pd(210) is studied. The conversion rate is accelerated with increasing surface temperature. Based on the conversion model proposed for metal surfaces, we analyze the temperature dependence of the conversion rate taking account of both electron and phonon systems of the substrate. The rotational-energy transfer is most likely mediated by surface electrons with an assistance of the substrate phonons.
津田 泰孝; Gueriba, J. S.*; 植田 寛和*; Di
o, W. A.*; 倉橋 光紀*; 岡田 美智雄*
JACS Au (Internet), 2(8), p.1839 - 1847, 2022/08
The orientation and motion of reactants play important roles in reactions. The small rotational excitations involved render the reactants susceptible to dynamical steering, making direct comparison between experiment and theory rather challenging. Using space quantized molecular beams, we directly probe the (polar and azimuthal) orientation dependence of O chemisorption on Cu
and Cu
Au. We observe polar and azimuthal anisotropies on both surfaces. Chemisorption proceeds rather favorably with the O-O bond axis oriented parallel (
perpendicular) to the surface, and also rather favorably with the O-O bond axis oriented along ![$$[001]$$](/search/images/ERNTAMBRLUSA.gif)
( along ![$$[bar{1}10]$$](/search/images/ERNVYYTBOJ3TC5JRGBOSI.gif)
). The presence of Au hinders the surface from further oxidation, introducing a higher activation barrier to chemisorption, and rendering an almost negligible azimuthal anisotropy. The presence of Au also prevents cartwheel-like rotating O from further reactions.
長屋 勇輝*; 中津 裕貴*; 小倉 正平*; 島崎 紘太*; 植田 寛和; 武安 光太郎*; 福谷 克之
Journal of Chemical Physics, 155(19), p.194201_1 - 194201_6, 2021/11
We have developed a spin-polarized-hydrogen beam with a hexapole magnet. By combining the beam chopper and pulsed laser ionization detection, the time-of-flight of the hydrogen beam was measured, and the dependence of the beam profile on the velocity was acquired, which was consistent with the beam trajectory simulations. The spin polarization of the beam was analyzed by using the Stern-Gerlach-type magnet in combination with the spatial scan of the detection laser. The spin polarization was about 95% at a focusing condition due to the hexapole magnet. The polarization was, on the other hand, reduced to about 70% for the beam at higher velocities, which is consistent with simulation results.
オルト-パラ転換植田 寛和; 福谷 克之
Vacuum and Surface Science, 64(9), p.430 - 434, 2021/09
A unique molecularly chemisorption of H occurs on some stepped surfaces in addition to the typical adsorption schemes of physisorption and dissociation. In the present study, the rotational state and 
conversion of the molecularly chemisorbed H on Pd(210) at a surface temperature of 50 K were probed by combining a pulsed molecular beam, photo-stimulated desorption and resonance-enhanced multiphoton ionization techniques. We experimentally demonstrated that the 
conversion proceeds with a conversion time constant of 
2s that is 2-3 orders of magnitude smaller than those reported for physisorption systems. The origins of such fast conversion and the rotational state distribution of H in molecular chemisorption state are discussed.
on Pd(210)植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 小倉 正平*; 福谷 克之
Physical Review B, 102(12), p.121407_1 - 121407_5, 2020/09
被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)Pd(210)表面に化学吸着したHのオルトーパラ転換を報告する。分子線,光刺激脱離,共鳴多光子イオン化法を用いて水素の回転状態変化を調べた。実験結果から、~2秒の転換時間で転換が起こることが明らかになった。実験結果と過去の理論計算結果を比較することで、2次の摂動による転換メカニズムを支持する。
椎名 陽子*; 高谷 一成*; 植田 寛和; 平山 孝人*; 中野 祐司*
Journal of Physics; Conference Series, 1412, P. 122021_1, 2020/06
A new development aiming experimental studies of isomer-selected gas-phase reactions and photoexcitation processes is being conducted. The experiment is based on isomer separation by an ion mobility spectrometry and ion accumulation in a temperature-variable radiofrequency ion trap. The laser plasma light source at Rikkyo University is currently under an upgrade for providing ultraviolet light at the wavelength region from 90 to 200 nm. We report on the details of the experimental setup and current status of the development.
on Pd(210)植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 福谷 克之
no journal, ,
On a flat metal surface, hydrogen typically chemisorbs dissociatively. On the other hand, it is known that hydrogen can molecularly chemisorbs on stepped surfaces, such as Ni(510) and Pd(210), in which the potential is expected to be highly anharmonic, unlike the case of physisorption. The anisotropic potential would modify the rotational state of H and promote ortho-para (o-p) conversion. For the system of H/Pd(210), a previous study with rotational-state-selective temperature programmed desorption indicated the occurrence of fast o-p conversion. In this study, to further probe the rotational state and conversion of molecularly chemisorbed H, a combination of photo-stimulated desorption and resonance-enhanced multiphoton ionization techniques is used. It is found that photo-desorbed H consists of a variety of rotational states with an anisotropic angular distribution. Photo-desorption and o-p conversion process will be discussed.
on Pd(210)植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 小倉 正平*; 福谷 克之
no journal, ,
Imperfections of the surface, such as steps, are known to affect adsorption and reaction processes. While hydrogen typically chemisorbs dissociatively on a flat metal surface, it is known that hydrogen can molecularly chemisorb on stepped surfaces, such as Ni(510) and Pd(210), in which the potential is expected to be highly anisotropic, unlike the case of physisorption. The anisotropic potential would modify the rotational state of H and promote ortho-para (o-p) conversion. For the system of H/Pd(210), the conversion time of ~1 sec was predicted based on the measurement on rotational-state-selective thermal desorption of H (J=0 and J=1). The predicted value is indeed much shorter than those in previously reported physisorption systems. In this contribution, to further probe the rotational state and conversion of molecularly chemisorbed H, a combination of a pulsed molecular beam, photo-stimulated desorption and resonance-enhanced multiphoton ionization techniques is used. We will present the rotational state distribution of photo-desorbed H, and the o-p conversion process of molecularly chemisorbed H will be discussed.
植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 福谷 克之
no journal, ,
一般的に平坦な金属表面では水素分子は解離吸着をするが、Pd(210)表面のようなステップ構造をもつ表面では、解離吸着のほか、分子状化学吸着することが知られている。本研究では、分子線, 光刺激脱離レーザーおよび共鳴多光子イオン化法を用いて、Pd(210)表面に分子状化学吸着した水素の回転状態を調べる。発表では、得られた光脱離水素分子の回転状態から化学吸着した水素分子の核スピン転換について議論する予定である。
植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 小倉 正平*; 福谷 克之
no journal, ,
一般的に平坦な金属表面では水素分子は解離吸着をするが、Pd(210)表面のような特異的なステップ構造を有する表面では、解離吸着のほか、分子状化学吸着することが知られている。吸着水素分子のオルト-パラ転換を調べるために、今回新たに分子線, 光刺激脱離および共鳴多光子イオン化法を組み合わせた測定手法を確立した。本発表では、この実験手法を用いて測定したPd(210)表面でのHのオルト-パラ転換時間について報告する。
植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 小倉 正平*; 福谷 克之
no journal, ,
水素分子は、Pd(210)表面のように特有なステップ構造をもつ表面では、解離吸着のほか分子状化学吸着する。本研究では、分子線, 光刺激脱離および共鳴多光子イオン化法を用いて、Pd(210)表面に化学吸着した水素分子のオルト-パラ転換を調べた。決定された転換時間は過去に報告されている物理吸着系(数百-千秒)と比べて大変短い2秒程度であった。発表では、測定結果とともに速い転換の起源について議論する予定である。
分子の解離吸着反応植田 寛和
no journal, ,
水蒸気改質反応の律速段階の一つであるメタンの解離反応は、表面科学的手法を用いてよく定義された条件下で研究されてきた。さらにレーザー技術の発達に伴い、メタン分子の量子状態を分解した反応素過程の理解が進んでおり、振動励起は解離反応で重要な役割を担っていることが分かってきている。本発表では、著者がかかわった白金表面における振動励起メタンの解離吸着反応研究を中心に紹介する。
植田 寛和; 笹川 裕矢*; Ivanov, D.*; 大野 哲*; 小倉 正平*; 福谷 克之
no journal, ,
表面温度50KでPd(210)表面に化学吸着した水素分子のオルト-パラ転換時間を測定した。実験の結果、転換時間は2秒程度であることが分かった。この時間は過去に2次摂動の転換モデルを基に見積もられた時間と同等であり、本研究はその転換モデルの正当性を支持する。
ortho-para conversion植田 寛和; 福谷 克之
no journal, ,
H has two nuclear spin isomers, ortho-H (o-H) and para-H (p-H). Due to symmetry restriction, o-H and p-H with parallel and antiparallel proton spins have odd and even rotational states, respectively. Interconversion between these two species, ortho-to-para (o-p) conversion is of great interest not only from a fundamental point of view but also in industrial applications such as H liquification and storage. While the radiative o-p conversion is forbidden in the gas phase, the conversion is promoted on various surfaces. The o-p conversion is completed by the nuclear spin flip and the rotational energy transfer. The former process has been paid much attention in previous o-p conversion studies, but the detail of the latter one remains unclear. In this contribution, we deal with the o-p conversion of molecularly chemisorbed H on Pd(210). This system allows us to probe the o-p conversion at a wider range of surface temperature as compared with physisorption systems. A combination of a pulsed molecular beam, photo-stimulated desorption and resonance-enhanced multiphoton ionization techniques is used to probe time evolution of o-H and p-H populations. Figure 1 shows that o-p conversion occurs with a conversion time of about 2 sec at a surface temperature of 50 K. To obtain insight into a role of rotational energy transfer in o-p conversion, we further study the surface temperature dependence of o-p conversion and the reverse process of p-o back conversion. From the results obtained the conversion mechanism will be discussed.
植田 寛和; 福谷 克之
no journal, ,
分子の固体表面への吸着には物理吸着と化学吸着があり、吸着状態によって分子の挙動は大きく変化する。水素は合成核スピンI=1のオルト水素とI=0のパラ水素が存在する。オルトとパラ間の転換は気相の孤立系では禁制であるが、固体表面に吸着すると促進されることが知られている。この水素オルト-パラ転換は基礎的な興味だけでなく、水素の液化に伴うボイルオフ問題や宇宙における分子雲での分子進化に関連して広く興味がもたれている。本講演では、物理吸着および化学吸着した水素のオルト-パラ転換について発表する。
on Pd(210)植田 寛和; 福谷 克之
no journal, ,
Clarifying energy transfer processes in molecular adsorption on solid surface is essential to understand gas/surface interaction. However, the rotational-energy transfer at surface remains less clear. The interconversion between ortho and para sates of H is accompanied by the nuclear spin flip and the rotational-energy transfer. We study the ortho-to-para (o-p) conversion of molecularly chemisorbed H on Pd(210) using a combination of a pulsed molecular beam, photo-stimulated desorption, and resonance-enhanced multiphoton ionization technique. In the present contribution, we present the surface temperature (TS) dependence of the o-p conversion rate in the temperature range of 40-60 K. It is found that the conversion rate accelerates with increasing TS. Based on the results obtained, the analysis of the rotational-energy of adsorbed H and the proposed rotational-energy transfer paths, we discuss the rotational-energy transfer process.
植田 寛和; 福谷 克之
no journal, ,
Energy transfer processes in molecular adsorption on solid surface are a key to understand gas/surface interaction. Recent experimental progress clarifies the vibrational-energy relaxation process of molecules on solid surfaces. However, its rotational-energy relaxation process still remains unclear. Molecular hydrogen has two nuclear spin isomers, ortho-H (o-H) and para-H (p-H). Due to symmetry restriction, o-H and p-H with parallel and antiparallel proton spins have odd and even rotational states, respectively. Interconversion between these two species, ortho-to-para (o-p) conversion is accompanied by the nuclear spin flip and the rotational-energy relaxation. The former has been discussed previously. In the present contribution, we deal with the rotational-energy transfer through the o-p conversion of molecularly chemisorbed H on Pd(210). A combination of a pulsed molecular beam, photo-stimulated desorption, and resonance-enhanced multiphoton ionization techniques is used for probing the time evolution of o-H and p-H populations. The surface temperature dependence of the o-p and its reverse process of para-to-ortho (p-o) conversions are studied. It is found that o-p conversion rate accelerates with increasing surface temperature. Furthermore, from a comparison between the o-p and p-o conversion rates, the o-p conversion rate is faster than that of p-o at the same surface temperature. Based on the results obtained and the analysis of the rotational-energy of adsorbed H, phonon- and electron-mediated paths are evaluated as a possible rotational-energy transfer process, and thereby it is likely that the former path is responsible.
植田 寛和; 大橋 悠生*; 石崎 雄士*; Sun, Z.-D.*; 小澤 孝拓*; 福谷 克之
no journal, ,
水素原子は陽子と電子一つずつからなり、それぞれ核スピンと電子スピンを持つ。近年、表面界面科学研究グループでは電子スピンを偏極した水素原子ビーム生成に成功している。このビームを用いて、試料位置での磁場を制御することで、電子スピンの向きを揃えた水素原子の表面吸着および引き抜き反応を調べた。試料表面に対する水素原子の電子スピンの向きによって、表面反応確率が異なることを見出した。
津田 泰孝; Gueriba, J. S.*; 植田 寛和; Dio, W. A.*; 倉橋 光紀*; 岡田 美智雄*
no journal, ,
The interaction of O with various metal surfaces induces changes in its chemical stability and reactivity. And the ability to control such processes bears on the chemical economy. Alloying of pristine metals provides one of the simplest and oldest way to do so. Unraveling the stereochemistry of the processes involved would be imperative for understanding the mechanisms behind of these interactions. The dynamics of reactant molecules (esp., the orientation and the movement of molecules in 3D space) plays an important role in reactions. The small rotational energy excitations involved (ca. less than a few meV) render the reactants susceptible to dynamical steering. This makes direct comparison with theory rather challenging. To directly probe and observe the (polar and azimuthal) orientation dependence of O adsorption on Cu(110) and CuAu(110), we prepared space quantized O molecular beams by sorting the quantum states of the O via Richtungsquantelung (space quantization, as first introduced by the 1922 Stern-Gerlach experiment). We found that chemisorption proceeded rather favorably with the O-O bond axis oriented parallel (vs. perpendicular) to the surface, and also for O-O bond axis oriented along [001] (vs. along [-110]). Alloying with Au introduced a higher activation barrier to chemisorption. This hinders the surface from further oxidation, and azimuthal anisotropy becomes almost negligible. The presence of Au also prevented cartwheel-like rotating O from further reactions.
