Ari Furuya

Increased Electric Conductance through Physisorbed Oxygen on Copper Nanocables Sheathed in Carbon

Adsorption of molecules onto solid surfaces can be classified into physisorption and chemisorption. Physisorbed molecules are so weakly bound to surfaces that adsorption and desorption can proceed reversibly even at room temperature. By contrast, chemisorption is accompanied by chemical bond formation, and higher temperatures are necessary for desorption. Solid gas sensors are normally based on chemisorption for modification of the electronic band conduction. We found that copper nanocables sheathed in carbon can detect physisorbed oxygen at room temperature by just measuring electric resistance. The sensing principle based on hopping conduction is specific to nanomaterials and enables detection of physisorbed oxygen.

Photodissociation of Mg+-XCH3 (X=F, Cl, Br, and I) complexes. I. Electronic spectra and dissociation pathways

Photodissociation spectra of Mg+-XCH3 (X=F, Cl, Br, and I) complexes have been measured in the ultraviolet region (225-415 nm). Several fragment ions with and without charge transfer (CT), Mg+, XCH3+, MgX+, MgCH3+, CH3+, and X+, were formed by evaporation (intermolecular bond dissociation) and intracluster reaction (intramolecular bond dissociation) via excited electronic states. Branching ratios of these ions were found to depend both on absorption bands and on halogen atoms. The ground states of the complexes were calculated to have geometries in which the Mg atom lies next to X atom of methyl halide molecules. Positive charges of the complexes are confirmed to be almost localized on Mg. Observed absorption bands were assigned to the transitions of the Mg+2P-2S atomic line perturbed by interactions with methyl halide molecules. Branching ratios of fragment ions can be partly explained by the stability of fragment ions and neutral counterparts. From the excited state potential energy curves along the Mg-X bond distance, dissociation reaction after CT was concluded to proceed predissociatively; potential curve crossings between the initially excited states and repulsive CT states may have a crucial role in the formation of CH3+, XCH3+, and X+. In particular, XCH3+ ions were formed via repulsive CT states having a character of electron excitation from Xnp to Mg+3s.

Photodissociation of Mg+–XCH3 (X=F, Cl, Br, and I) complexes. II. Fragment angular and energy distributions

Angular and energy distributions of photofragments from Mg+-XCH3 (X=F, Cl, Br, and I) were deduced from time-of-flight (TOF) profiles measured by rotating the polarization direction of the dissociation laser with respect to ion beam direction. The TOF profiles of ICH3+ and MgI+ fragment ions produced from Mg+-ICH3 complex with 266 and 355 nm photons showed clear but opposite recoil anisotropy to each other. In addition, BrCH3+ formed by a dissociation of the Mg+-BrCH3 complex at a photolysis wavelength of 266 nm also showed an anisotropic distribution in the TOF profile which had the same behavior as the profile of ICH3+. For Mg+-FCH3 complex, CH3+ and MgF+ formed with a 266 nm photon had also spatial anisotropy, in which the TOF profile of MgF+ was almost opposite to that of MgI+. These anisotropic distributions were explained by (1) local excitation on the Mg+ ion, (2) rapid dissociation compared with a rotational period of the parent complex, and (3) geometrical structures of the parent complexes. Anisotropy beta parameter values were determined to be +1.30(ICH3+), -0.50(MgI+), +0.74(BrCH3+), and +0.75(CH3+ and MgF+). This dependence on the halogen atom observed in beta values was qualitatively explained by both the geometrical parameters and classical rotational periods of parent complexes. In the product energy distribution, 46%, 40%, 21%, 16%, and 16% of available energies were found to be transferred into translational energies of ICH3+, MgI+, BrCH3 +, CH3+, and MgF+, respectively. These values were compared with energy distributions estimated by a statistical prior distribution and a nonstatistical impulsive model. For ICH3+ and MgI+, the translational energies determined from the measurement had values between those estimated from statistical and nonstatistical models. On the other hand, the energy partitioning for the product ions of BrCH3+, CH3+, and MgF+ was found to be almost statistical. From these considerations, we concluded that nonstatistical processes were more important in the dissociation of Mg+-ICH3 than in other systems.

Adsorption of small molecules with the hydroxyl group on sodium halide cluster ions.

We have investigated adsorption of molecules with hydroxyl group, ROH, on sodium halide cluster ions, Na(n)X(n-1)(+) (X = F and I, n = 10-17) by mass spectrometry and by theoretical calculations. From analysis of the cluster ion intensities, the adsorption of one water molecule (R = H) is most efficient for Na(13)X(12)(+), whose structure has a NaX defect from a 3 x 3 x 3 cubic structure of n = 14. This result suggests that the defect has an important role in the adsorption reaction. However, it is also found that the reactivity diminishes with increasing bulk size of the R group from H to CH(3), (CH(3))(2)CH, and (CH(3))(3)C. These results imply that the adsorption reactivity is dominated by steric hindrance; the smaller molecules are adsorbed inside the basket structures of Na(13)X(12)(+). Reactivity dependence on the basket size is also discussed by comparing the results of Na(n)F(n-1)(+) and Na(n)I(n-1)(+).

Photodissociation of Mg(CH2=CHCN)n+: Excited electronic states of n=1 and 2 and intracluster electron transfer for n=3 and 4

Photodissociation spectra of mass-selected Mg(CH2=CHCN)n+ cluster ions were investigated in the wavelength region from 415 to 225 nm and 495 to 225 nm for n=1 and 2, respectively, by monitoring the total yield of fragment ions. The absorption bands exhibit large shifts from the 2P–2S resonance line of Mg+. In the spectrum of n=1, there are two bands at 26 400 and 40 800 cm−1. On the other hand, three absorption bands at 22 600, 28 800, and 37 500 cm−1 appear in the spectrum of n=2. The most stable structures in the ground state for n=1 and 2 were obtained by DFT(B3LYP/6-31+G*) calculations, and transition energies from these structures were obtained by using configuration interaction singles approach with the same basis set. The calculated excitation energies show good agreement with the experimental results. In addition, fragment ions of Mg(CH2=CHCN)m+ with m=4 and 5 are found to have high intensities from the parent ions of n=6–10 at a dissociation wavelength of 355 nm. From the result of theoretical ca...

Photoionization mass spectroscopy of clusters of alkali metal atoms with methyl vinyl ketone and acrolein: intracluster oligomerization initiated by electron transfer from a metal atom

Abstract We have investigated the photoionization mass spectrometry of clusters of an alkali metal atom (M: Na and K) and methyl vinyl ketone (MVK) or acrolein (AC) to discuss the intracluster oligomerization. In the mass spectra of M(MVK) n , strong ion signals at n =3 are observed. This magic number is explained by the cyclohexane derivative formation in the intracluster oligomerization of MVK initiated by electron transfer from an alkali metal atom. The results of the calculation for Na(MVK) based on density functional theory also show the presence of intracluster electron transfer. On the other hand, in M(AC) n , intensity enhancement is observed at n =4. These intensity enhancements may be due to intracluster reaction in M(AC) n , which is different from the case of M(MVK) n .

Size-dependent structures of NanIn−1+ cluster ions with a methanol adsorbate: A combined study by photodissociation spectroscopy and density-functional theory calculation

Methanol adsorption sites on NanI+n-1 ions were investigated. Photoexcitation to charge-transfer states of NanI+n-1 (methanol) predominantly produces two fragment ions: Nan-1I+n-2 (methanol) (neutral NaI loss) and Nan-1I+n-2(neutral NaI and methanol loss), without forming NanI+n-1 (methanol loss). The relative intensities of these fragments are correlated with the geometries and binding energies.

ADSORPTION REACTION OF POLAR ORGANIC MOLECULES ON

We have examined chemical reactions of small silicon cluster ions for n = 7 - 16 with polar organic molecules M (M = CH3CN, CD3OD, C2H5CN, and C2H5OH). The intensities of the adsorption products for m = 1 and 2 were investigated as a function of n. We found for all polar molecules that the relative intensity of SinM+ to the unreacted is smaller for n = 11, 13, and 14, that is, the adsorption reactivity is smaller for these n than others. It was also commonly observed that the ion are more intense than neighboring n. We discussed the relationship of the reactivity with the geometrical structures and the stabilities of the bare ions and adsorbed ions, from theoretical calculations based on density functional theory.