||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..
||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..
||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.
||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..
||Masashi Arakawa, Kei Kohara, Tomonori Ito, Akira Terasaki, Size-dependent reactivity of aluminum cluster cations toward water molecules, European Physical Journal D, 2013.04.
||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.
||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.
||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.
||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.
||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.