Author
Keijiro Ohshimo
Other affiliations: National Institutes of Natural Sciences, Japan
Bio: Keijiro Ohshimo is an academic researcher from Tohoku University. The author has contributed to research in topics: Ion & Mass spectrum. The author has an hindex of 14, co-authored 62 publications receiving 652 citations. Previous affiliations of Keijiro Ohshimo include National Institutes of Natural Sciences, Japan.
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TL;DR: In this paper, cluster geometries are optimized and vibrational frequencies are evaluated by density functional theory calculation, and the most stable isomer of [Mg·(H2O)4]- has a six-membered ring composed of the Mg+ ion, two of the three water molecules in the first solvation shell; the fourth molecule is bonded to the first Solvation shell.
Abstract: Infrared photodissociation spectra of [Mg·(H2O)1-4]+ and [Mg·(H2O)1-4·Ar]+ are measured in the 3000−3800 cm-1 region For [Mg·(H2O)1-4]+, cluster geometries are optimized and vibrational frequencies are evaluated by density functional theory calculation We determine cluster structures of [Mg·(H2O)1-4]+ by comparison of the infrared photodissociation spectra with infrared spectra calculated for optimized structures of [Mg·(H2O)1-4]+ In the [Mg·(H2O)1-3]+ ions, all the water molecules are directly bonded to the Mg+ ion The infrared photodissociation spectra of [Mg·(H2O)4]+ and [Mg·(H2O)4·Ar]+ show bands due to hydrogen-bonded OH stretching vibrations in the 3000−3450 cm-1 region In the [Mg·(H2O)4]+ ion, three water molecules are attached to the Mg+ ion, forming the first solvation shell; the fourth molecule is bonded to the first solvation shell As a result, the most stable isomer of [Mg·(H2O)4]+ has a six-membered ring composed of the Mg+ ion, two of the three water molecules in the first solvation sh
57 citations
TL;DR: In this paper, the authors measured the infrared spectra of [Mg·-H2O)1,2]- and [Al·−(H 2O)2]- ion and assigned a band at 3200-3800 cm−1.
52 citations
TL;DR: Arrival time distributions in the ion mobility spectrometry indicate that two structural isomers coexist for the (FeO)n(+) clusters at n ≥ 5, and compact three-dimensional structures were also found to be stable at (FenOn + 1(+) (n ≥ 6).
Abstract: Geometrical structures of iron oxide cluster cations have been analyzed by ion mobility mass spectrometry. The series of (FeO)n+ and FenOn + 1+ cluster cations were predominantly observed in a mass spectrum at high ion-injection energy into a drift cell. Arrival time distributions in the ion mobility spectrometry indicate that two structural isomers coexist for the (FeO)n+ clusters at n ≥ 5. By comparison of experimental collision cross sections determined from the arrival times with theoretical ones, two-dimensional ring and sheet structures were assignable for (FeO)n+ (n = 3–8). In addition to these isomers, compact three-dimensional structures were also found to be stable at (FeO)n+ (n ≥ 6). Thus, the two-dimensional and three-dimensional structural isomers coexist for (FeO)n+ (n = 6–8).
49 citations
TL;DR: In this paper, collision cross sections of cobalt oxide cluster cations have been determined for (CoO ) 2 - 7 + and Co n O n - 1 + (n ǫ = 5 − 7) orientation-averaged collision crosssections were calculated for optimized structures of these ions obtained in quantum chemical calculations.
38 citations
TL;DR: The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to theD0 continuum.
Abstract: We have studied 3s(n-1 and π-1) Rydberg states and D0(n-1) and D1(π-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV−PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck−Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1−D0 and 3s(π-1)−3s(n-1) conical intersectio...
37 citations
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TL;DR: In this article, the adsorption equilibrium selectivity was calculated from the ratio of Henry's constants, and the adsorbent selection parameter for pressure swing adaption was determined gravimetrically at 298 K and elevated pressures (14 bar for CO2 and 100 bar for CH4).
Abstract: Adsorption equilibrium and kinetics of CO2, CH4, N2O, and N2 on two newly discovered adsorbents, metal-organic frameworks MOF-5 and MOF-177 and one traditional adsorbent, zeolite 5A were determined to assess their efficacy for CO2, CH4, and N2O removal from air and separation of CO2 from CH4 in pressure swing adsorption processes. Adsorption equilibrium and kinetics data for CO2, CH4, N2O, and N2 on all three adsorbents were measured volumetrically at 298K and gas pressures up to 800 Torr. Adsorption equilibrium capacities of CO2 and CH4 on all three adsorbents were determined gravimetrically at 298 K and elevated pressures (14 bar for CO2 and 100 bar for CH4). The Henry’s law and Langmuir adsorption equilibrium models were applied to correlate the adsorption isotherms, and a classical micropore diffusion model was used to analyze the adsorption kinetic data. The adsorption equilibrium selectivity was calculated from the ratio of Henry’s constants, and the adsorbent selection parameter for pressure swing ...
659 citations
319 citations
TL;DR: A review of gas phase IRMPD spectroscopic investigations aiming at probing the structure and the reactivity of transition metal complexes and a special attention will be given to the infrared spectroscopy of reactive intermediates.
Abstract: Gas phase mid-infrared spectroscopy of molecular ions can nowadays be performed with high performance mass spectrometers coupled to free electron lasers (FEL). The wide and continuous tunability of highly intense FELs in the mid-infrared region can be exploited for performing infrared multiple photon dissociation (IRMPD) spectroscopy of molecular ions. This review will focus on gas phase IRMPD spectroscopic investigations aiming at probing the structure and the reactivity of transition metal complexes. The performance of infrared spectroscopy for characterizing the coordination mode of polydentate ligands and the spin state of the metal will be illustrated. Infrared spectroscopy has also been exploited to probe the reactivity of metal complexes, and a special attention will be given to the infrared spectroscopy of reactive intermediates.
274 citations
TL;DR: In this review, the preparation methods, crystal structures, physicochemical properties, and practical applications of Au25(SR)18 are summarized and some perspectives and challenges for the future research of the Au 25( SR)18 nanocluster are proposed.
Abstract: Noble metal nanoclusters are in the intermediate state between discrete atoms and plasmonic nanoparticles and are of significance due to their atomically accurate structures, intriguing properties, and great potential for applications in various fields. In addition, the size-dependent properties of nanoclusters construct a platform for thoroughly researching the structure (composition)-property correlations, which is favorable for obtaining novel nanomaterials with enhanced physicochemical properties. Thus far, more than 100 species of nanoclusters (mono-metallic Au or Ag nanoclusters, and bi- or tri-metallic alloy nanoclusters) with crystal structures have been reported. Among these nanoclusters, Au25(SR)18—the brightest molecular star in the nanocluster field—is capable of revealing the past developments and prospecting the future of the nanoclusters. Since being successfully synthesized (in 1998, with a 20-year history) and structurally determined (in 2008, with a 10-year history), Au25(SR)18 has stimulated the interest of chemists as well as material scientists, due to the early discovery, easy preparation, high stability, and easy functionalization and application of this molecular star. In this review, the preparation methods, crystal structures, physicochemical properties, and practical applications of Au25(SR)18 are summarized. The properties of Au25(SR)18 range from optics and chirality to magnetism and electrochemistry, and the property-oriented applications include catalysis, chemical imaging, sensing, biological labeling, biomedicine and beyond. Furthermore, the research progress on the Ag-based M25(SR)18 counterpart (i.e., Ag25(SR)18) is included in this review due to its homologous composition, construction and optical absorption to its gold-counterpart Au25(SR)18. Moreover, the alloying methods, metal-exchange sites and property alternations based on the templated Au25(SR)18 are highlighted. Finally, some perspectives and challenges for the future research of the Au25(SR)18 nanocluster are proposed (also holding true for all members in the nanocluster field). This review is directed toward the broader scientific community interested in the metal nanocluster field, and hopefully opens up new horizons for scientists studying nanomaterials. This review is based on the publications available up to March 2018.
217 citations
TL;DR: The capabilities and the potential of PECD are illustrated with various experimental examples and computational methods that are able to model quantitatively experimental PECD results are introduced, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured.
Abstract: In this Perspective we discuss photoelectron circular dichroism (PECD), a relatively novel technique that can detect chiral molecules with high sensitivity. PECD has an enantiomeric sensitivity of typically 1–10%, which is two to three orders of magnitude larger than that of the widely employed technique of circular dichroism (CD). In PECD a chiral molecule is photoionized with circular polarized light, and the photoelectron angular scattering distribution is detected using particle imaging techniques. We present the general physical principles of photoelectron circular dichroism and we address both single- and multiphoton excitation. PECD has been measured with synchrotron radiation in single-photon ionization as well as, very recently, with femtosecond laser radiation in multiphoton ionization. We discuss the experimental implementation of PECD, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured. The coincident detection of the mass and momentum of the ion adds very powerful mass-correlated information to the PECD measurement of the chiral molecule. We illustrate the capabilities and the potential of PECD with various experimental examples and introduce computational methods that are able to model quantitatively experimental PECD results. We conclude with an outlook on novel developments and (analytical) implementations of PECD that may further broaden the application of PECD for the sensitive detection of chirality in molecules.
159 citations