| 1. |
Masashi Arakawa, Naho Hayashi, Kento Minamikawa, Tasuku Nishizato, and Akira Terasaki, Exploring s–d, s–f, and d–f Electron Interactions in AgnCe+ and AgnSm+ by Chemical Reaction toward O2, Journal of Physical Chemistry A, 10.1021/acs.jpca.2c04941, 126, 6920-6926, 2022.10, We investigate gas-phase reactions of free AgnCe+ and AgnSm+ clusters with oxygen molecules to explore s–d, s–f, and d–f electron interactions in the finite size regime; a Ce atom has a 5d electron as well as a 4f electron, whereas a Sm atom has six 4f electrons without 5d electrons. In the reaction of AgnCe+ (n = 3–20), the Ce atom located on the cluster surface provides an active site except for n = 15 and 16, as inferred from the composition of the reaction products with oxygen bound to the Ce atom as well as from their relatively high reactivity. The extremely low reactivity for n = 15 and 16 is due to encapsulation of the Ce atom by Ag atoms. The minimum reactivity observed at n = 16 suggests that a closed electronic shell with 18 valence electrons is formed with a delocalized Ce 5d electron, while the localized Ce 4f electron does not contribute to the shell closure. As for AgnSm+ (n = 1–18), encapsulation of the Sm atom was observed for n ≥ 15. The lower reactivity at n = 17 than at n = 16 and 18 implies that an 18-valence-electron shell closure is formed with s electrons from Ag and Sm atoms; Sm 4f electrons are not involved in the shell closure as in the case of AgnCe+. The present results suggest that the 4f electrons tend to localize on the lanthanoid atom, whereas the 5d electron delocalizes to contribute to the electron shell closure.. |
| 2. |
M. Arakawa, M. Horioka, K. Minamikawa, T. Kawano, and A. Terasaki, Reaction of nitric oxide molecules on transition-metal-doped silver cluster cations: Size- and dopant-dependent reaction pathways, Physical Chemistry Chemical Physics, 10.1039/D1CP02882K, 23, 22947-22956, 2021.09, We report size- and dopant-dependent reaction pathways as well as reactivity of gas-phase free AgnM+ (M = Sc–Ni) clusters interacting with NO. The reactivity of AgnM+, except for M = Cr and Mn, exhibits a minimum at a specific size, where the cluster cation possesses 18 or 20 valence electrons consisting of Ag 5s and dopant’s 3d and 4s. The product ions range from NO adducts, AgnM(NO)m+, and oxygen adducts, AgnMOm+, to NO2 adducts, AgnM(NO2)m+. At small sizes, AgnMOm+ are the major products for M = Sc–V, whereas AgnM(NO)m+ dominate the products for M = Cr–Ni in striking contrast. In both cases, these reaction products are reminiscent of those from an atomic transition metal. However, the reaction pathways are different at least for M = Sc and Ti; kinetics measurements reveal that the present oxygen adducts are formed via NO adducts, while, for example, Ti+ is known to produce TiO+ directly by reaction with a single NO molecule. At larger sizes, on the other hand, AgnM(NO2)m+ are dominantly produced regardless of the dopant element because the dopant atom is encapsulated by the Ag host; the NO2 formation on the cluster is similar to that reported for undoped Agn+.. |
| 3. |
Masashi Arakawa, Masataka Horioka, Kento Minamikawa, Tomoki Kawano, and Akira Terasaki, Reaction kinetics of nitric oxide on size-selected silver cluster cations, Journal of Physical Chemistry C, 10.1021/acs.jpcc.0c08890, 124, 26881-26888, 2020.11, We report reactions of gas-phase free silver cluster cations, Agn+ (n
= 3−18), with nitric oxide molecules, which was studied by kinetics
measurements using an ion trap. AgnO(NO2)m−1+ and Agn(NO2)m+ were
observed as major products after multiple reactions. The reaction pathway to
form these product ions was identified by fitting the data to rate equations for n ≤
15, except for inert n = 3 and 5. Two different reaction mechanisms were found
for the formation of these products depending on cluster size; pseudo-first-order
rate constants of each step of elementary reactions were obtained. First, as found
for n = 4, 6, and 9, AgnO+ is formed by a reaction with two NO molecules, which
is followed by a release of neutral N2O. A further reaction of AgnO+ with another
NO molecule produces AgnNO2+. Agn(NO2)m+ (m ≥ 1) is thus successively
formed via an intermediate, AgnO(NO2)m−1+. This is analogous to the reaction of
NO on silver surfaces to produce NO2. Second, both AgnNO2+ and AgnO+ are formed concurrently, as found for n = 7, 8, 10, 11, 12, and 15; AgnO+ does not act as an intermediate for AgnNO2+. AgnO(NO2)m−1+ and Agn(NO2)m+ (m ≥ 2) are formed by successive addition of NO2 to AgnO+ and AgnNO2+, respectively. It is speculated that the successive addition of NO2 proceeds via disproportionation, i.e., three NO molecules are converted to NO2 and N2O. The reaction pathways of n = 13 and 14 are explained equally well by the two mechanisms. The overall reaction rate coefficients exhibit an odd−even alternation; the higher reactivity for even values of n is due to an odd number of valence electrons.. |
| 4. |
Masashi Arakawa, Daichi Okada, Satoshi Kono, and Akira Terasaki, Preadsorption effect of carbon monoxide on reactivity of cobalt cluster cations toward hydrogen, Journal of Physical Chemistry A, 10.1021/acs.jpca.0c05819, 124, 9751-9756, 2020.10, We report gas-phase reactions of free Con(CO)+m (n = 3−11, m = 0−2) with H2, expecting a catalytic reaction of coadsorbed CO and H2 on Co+n. Preadsorption of CO molecules is found to promote H2 adsorption, in particular, on Con(CO)+ (n = 5, 8−10). Density functional theory (DFT) calculations reveal that the reactivity is governed by the molecular-orbital energy of Co+n, which is tuned by preadsorbed CO molecules. Collision-induced-dissociation experiments performed on ConCOH+2 (n = 8−10) imply that at least some of the CO and H2 molecules are bound together on Co+n.. |
| 5. |
Shun Sarugaku, Masashi Arakawa, Tomoki Kawano, Akira Terasaki, Electronic and geometric effects on chemical reactivity of 3d-transition-metal-doped silver cluster cations toward oxygen molecules, Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b05117, 123, 25890-25897, 2019.10, We report electronic and geometric structures of 3d-transition-metal-doped silver cluster cations, AgN−1M+ (M = Sc−Ni), studied by chemical reaction with oxygen molecules. The evaluated reaction rate coefficients for small sizes, N, are 2− 6 orders of magnitude higher than those of undoped AgN+, whereas those for large N are comparable with those of AgN+. The low reactivity at large sizes is attributed to a geometric effect, that is, encapsulation of the dopant atom, which provides an active site located on the surface of the cluster in small sizes. In addition, a reactivity minimum is observed for AgN−1M+ with M = Sc, Ti, V, Fe, Co, and Ni at a specific size, where the cluster possesses 18 valence electrons including 3d electrons. With the aid of density functional theory calculations, the reactivity minimum is suggested to be due to an electronic effect, that is, formation of a closed electronic shell by the 18 valence electrons, implying delocalized 3d electrons. Ag13Cr+ and Ag12Mn+, possessing 18 valence electrons as well, are noted to be exceptions, where d electrons are supposed to be localized on the dopant atom because of the half-filled nature of Cr and Mn 3d orbital.. |
| 6. |
M. Arakawa, K. Ando, S. Fujimoto, S. Mishra, G. Naresh Patwari, and A. Terasaki, The role of electronegativity on the extent of nitridation of group 5 metals as revealed by reactions of tantalum cluster cations with ammonia molecules, Physical Chemistry Chemical Physics, 10.1039/c8cp00424b, 20, 13794-13982, 2018.04, Reactions of the free tantalum cation, Ta+, and tantalum cluster cations, Tan+ (n = 2–10), with ammonia are presented. The reaction of the monomer cation, Ta+, with two molecules of NH3 leads to the formation of TaN2H2+ along with release of two H2 molecules. The dehydrogenation occurs until the formal oxidation number of the tantalum atom reaches +5. On the other hand, all the tantalum cluster cations, Tan+, react with two molecules of NH3 and form TanN2+ with the release of three H2 molecules. Further exposure to ammonia showed that TanNmH+ and TanNm+ are produced through successive reactions; a pure nitride and three H2 molecules are formed for every other NH3 molecule. The nitridation occurred until the formal oxidation number of the tantalum atoms reaches +5 as in the case of TaN2H2+ in contrast to other group 5 elements, i.e., vanadium and niobium, which have been reported to produce nitrides with lower oxidation states. The present results on small gas-phase metal- nitride clusters show correlation with their bulk properties: tantalum is known to form bulk nitrides in the oxidation states of either +5 (Ta3N5) or +3 (TaN), whereas vanadium and niobium form nitrides in the oxidation state of +3 (VN and NbN). Along with DFT calculations, these findings reveal that nitridation is driven by the electron-donating ability of group 5 elements, i.e., electronegativity of the metal plays a key role in determining the composition of the metal nitrides.. |
| 7. |
Masashi Arakawa, Tsubasa Omoda, Akira Terasaki, Adsorption and Subsequent Reaction of a Water Molecule on Silicate and Silica Cluster Anions, Journal of Physical Chemistry C, 10.1021/acs.jpcc.6b11689, 2017.01, We present reactions of size-selected free silicate, MglSiOm−, and silica, SinOm−, cluster anions with a H2O molecule focusing on H2O adsorption. It was found that H2O adsorption to MglSiOm− with l = 2 and 3 (m = 4−6) is always followed by molecular oxygen release, whereas reactivity of the clusters with l = 1 (m = 3−5) was found to be much lower. On the contrary, in the reaction of SinOm− (n = 3−8, 2n − 1 ≤ m ≤ 2n + 2), a H2O adduct is observed as a major reaction product. Larger and oxygen- rich clusters tend to exhibit higher reactivity; the rate constants of the adsorption reaction are 2 orders of magnitude larger than those of CO adsorption previously reported. DFT calculations revealed that H2O is dissociatively adsorbed on SinOm− to form two SiO3(OH) tetrahedra. The site selectivity of H2O adsorption is governed by the location of the singly occupied molecular orbital (SOMO) on SinOm−. The present findings give molecular-level insights into H2O adsorption on silica and silicate species in the interstellar environment.. |
| 8. |
Masashi Arakawa, Ryo Yamane, Akira Terasaki, Reaction sites of CO on size-selected silicon-oxide cluster anions: a model study of chemistry in the interstellar environment, Journal of Physical Chemistry A, 10.1021/acs.jpca.5b08900, 120, 139-144, 2016.01. |
| 9. |
Masashi Arakawa, Kei Kohara, Akira Terasaki, Reaction of aluminum cluster cations with a mixture of O2 and H2O gases: Formation of hydrated-alumina clusters, Journal of Physical Chemistry C, 10.1021/jp511293g, 119, 10981-10986, 2015.04, We present reactions of size-selected free aluminum cluster
cations, AlN+ (N = 1−14), exposed to a mixture of water and oxygen gases.
It is featured that chemical species assignable to Al2O6H7+ and Al2O7H9+
were commonly produced as prominent reaction products from all of the
sizes, except N = 1. These product ions were found to be produced via the
formation of Al2O3+ in the initial stage of reactions with O2 and H2O,
which was followed by successive hydrogenation and hydration. This
reaction pathway was identified by examining reactivity of each
intermediate product step by step. Structures of the product ions were
analyzed by collision-induced dissociation experiments and DFT calculations; for+ example, coexistence of isomers, Al2O5H5(H2O)+ and
Al2O4H3(H2O)2 , with one and two intact H2O molecules, respectively, was suggested for Al2O6H7+. The chemical compositions of the ions +
produced in the present reactions are expressed nominally as Al2O3(H2O)nH , which is similar, except for the proton, to that of hydrated alumina, that is, forms of bulk aluminum abundant naturally. The present finding gives molecular-level insights into formation processes of aluminum minerals in a natural environment.. |
| 10. |
Masashi Arakawa, Kei Kohara, Tomonori Ito, Akira Terasaki, Size-dependent reactivity of aluminum cluster cations toward water molecules, European Physical Journal D, 2013.04. |
| 11. |
Arakawa M., Kagi H., Fernandez-Baca J. A., Chakoumakos B. C. and Fukazawa H., The existence of memory effect on hydrogen ordering in ice: The effect makes ice attractive, Geophysical Research Letters, in press, 2011.08. |
| 12. |
Arakawa M., Kagi H. and Fukazawa H., Annealing effects on hydrogen ordering in KOD-doped ice observed using neutron diffraction, Journal of Molecular Structure, doi:10.1016/j.molstruc.2010.02.016, 982, 111, 2010.03. |
| 13. |
Arakawa M., Kagi H. and Fukazawa H., Laboratory measurements of infrared absorption spectra of hydrogen-ordered ice: a step to the exploration of ice XI in space, Astrophysical Journal Supplement Series, doi:10.1088/0067-0049/184/2/361, 184, 361-365, 2009.09. |
| 14. |
Arakawa M., Yamamoto J. and Kagi H., Developing micro-Raman mass spectrometry for measuring carbon isotopic composition of carbon dioxide, Applied Spectroscopy, doi:10.1366/000370207781393244, 61, 701-705, 2007.07. |
| 15. |
Arakawa M., Yamamoto J. and Kagi H., Micro-Raman thermometer for CO2 fluids: Temperature and density dependence on Raman spectra of CO2 fluids, Chemistry Letters, doi:10.1246/cl.2008.280, 37, 280-281, 2008.02. |
