Photofragmentation of mass-selected titanium oxide cluster cations

In this paper we present the photofragmentation spectra of mass-selected positive titanium oxide cluster ions Ti _x O _y ⁺. The clusters are generated by the combination of laser ablation of a titanium target and the supersonic nozzle expansion of oxygen and are detected by time-of-flight mass spectrometry. Small clusters are mass-selected and photodissociated at a wavelength of 308 nm. The recorded photofragmentation spectra indicate that for all parent clusters the main fragment is TiO⁺ and, in some cases, Ti₂O₃ ⁺ is also observed. This is consistent with the assumption that small Ti _x O _y ⁺ clusters are built from a TiO⁺ core with TiO₂ building blocks.     

Collision-induced fragmentation and neutralization of methanol cluster cations

This contribution addresses the inelastic interaction of positively charged molecular cluster ions with a solid surface at kinetic energies up to 30 eV/molecule. We report experimental results on the scattering of mass-selected, protonated methanol cluster cations (CH₃OH)_nH⁺, n = 4-32, off a diamond-coated silicon surface. In particular we provide fragment size distributions of methanol cluster ions following their impact on the target, as well as surface-induced neutralization probabilities of methanol cluster ions as a function of the size and the kinetic energy of the parent clusters. Received 30 November 2000     

Infrared multiple photon dissociation spectroscopy of transition metal oxide cluster cations

Infrared spectra in the range of 530–1400 cm^–1 are presented for tantalum oxide cluster cations (x = 3, 4 and 6). These spectra are obtained via multiple photon dissociation (MPD) spectroscopy of free cluster cations moving in a molecular beam. The IR spectra for are compared to spectra of as well as to the experimental data available for vanadium oxide cluster cations from IR-MPD spectroscopy. For and the IR spectra exhibit very strong similarities (including the band positions), whereas absorption bands in are relatively blue-shifted by about 20–40 cm^–1.     

Collision-induced dissociation of alkyl alcohols

collision-induced dissociation of aliphatic alcohols by I₂⁺, I⁺ and Xe⁺ ions is studied using a double mass spectrometer of the longitudinal type. The fragmentation patterns are compared with those resulting from pure charge exchange obtained with a double mass spectrometer of the perpendicular type. Important differences are pointed out, the former reactions being more complicated than the latter.     

Collision-induced dissociation of H 3 + ions

For collision energies between 100 and 500 eV the collision induced dissociation of H ₃ ⁺ colliding with H₂, He and Kr gas targets was measured. We obtained total cross sections and angular distributions of the charged collision fragments for the main reaction channels. H ₃ ⁺ +H₂→H⁺+2H² and H ₃ ⁺ +H₂→H ₂ ⁺ +H₂+H. An analysis of the kinetics yields that the dissociation proceeds via vibrational-rotational excitation of H ₃ ⁺ by mutually induced dipolmoments.     

Isomer-selected photoreactions of gas-phase cluster ions

We have developed an apparatus for investigating isomer-selected photodissociation reactions by ion mobility spectrometry coupled with time-of-flight mass spectrometry. By using this apparatus we optimized ion intensities under isomer-separation condition for carbon cluster ions. Among ions having linear and cyclic isomers, we demonstrated dissociation of isomer-selected C₉ ⁺ ion at 355-nm photon irradiation. As a result we observed marked difference in the dissociation pathways between from linear isomer and from cyclic isomer. For the purpose of adopting this technique to metal-ligand cluster ions, we also investigated mobility spectrometry of vanadium metal ions with Ar, in addition to electronic state separation for free atomic ions.     

Release studies of corrosion inhibitors from cerium titanium oxide nanocontainers

Cerium titanium oxide nanocontainers were synthesized through a two-step process and then loaded with corrosion inhibitors 2-mercaptobenzothiazole (2-MB) and 8-hydroxyquinoline (8-HQ). First, polystyrene nanospheres (PS) were produced using polymerization in suspension. Second, the PS spheres were coated via the sol–gel method to form a cerium titanium oxide layer. Finally, the nanocontainers were made by calcination of the coated PS nanospheres. The size of the containers was 180 ± 10 nm as determined by Scanning Electron Microscopy (SEM). X-Ray Diffraction Analysis (XRD) showed that the nanocontainers consist of anatase and cerianite crystalline phases. The presence and loading of the inhibitors in the nanocontainers was confirmed with Fourier Transform Infrared Spectroscopy (FT–IR) and Thermo Gravimetric Analysis (TGA), respectively. TGA revealed the amount of 10.43 and 4.61% w/w for 2-MB and 8-HQ in the nanocontainers, respectively. Furthermore, the release kinetics of the inhibitors from the nanocontainers was studied in corrosive environment using electrochemical impedance spectroscopy (EIS) in the presence of aluminum alloys 2024-T3 (AA2024-T3).     

Difference in formation of carbon cluster cations by laser ablation of graphene and graphene oxide

The distributions of positive carbon cluster ions produced by laser ablation of graphene (G) and graphene oxide (GO) are found to be quite different. Under a typical experimental condition, narrow distributions of even-numbered clusters from C60+ to C162+ were observed for G, and broad distributions including even-numbered clusters from C100+ to C400+ and odd-numbered clusters from C189+ to C395+ were observed for GO. The threshold of laser energy for G is lower than that of GO. Further results of collision-activated dissociation mass spectrometry indicate that the cluster ions generated from G are structurally similar but are different with those generated from GO or nanodiamonds. It is proposed that the experimentally observed difference can be attributed to the different mechanisms behind the process. A top-down mechanism including both direct transformation of G to fullerene and fragmentation of large-sized fullerenes is suggested for the generation of carbon cluster cations in the process of laser ablation of G. For GO, the experimental results are close to those of nanodiamonds and other materials reported previously and can be explained by the generally accepted bottom-up mechanism.     

Photoemission and coincidence studies on gas-phase molecules

This article describes Young’s double-slit experiment using high-energy core-level photoemission from N₂ molecules and experimental identification of interatomic Coulombic decay in Ar₂ dimers after Auger decay using k-resolved electron–ion–ion coincidence spectroscopy, aiming to illustrate the leading edge of gas-phase experiments using synchrotron radiation.     

Hyperthermal surface-collisions of water cluster cations

Size-selected, protonated water cluster cations (H₂O)_nH⁺, 4 n 32, are scattered at normal incidence from the surface of a diamond-coated silicon wafer at collision energies 0 E _coll 500 eV. The size distribution of collision-induced fragment-ions and the ion yield of scattered particles are analyzed, using a secondary time-of-flight mass spectrometer, as a function of the cluster size, n, and the collision energy, E _coll. Even at low impact energies only very small fragment-ions can be detected, with a maximum fragment size of 35% of the colliding parent cluster ions. For clusters consisting of more than 10 molecules, the protonated water dimer (H₂O)₂H⁺ becomes the predominant fragment-ion. The total charge survival yield obeys a nonlinear increase with cluster size; for the largest clusters investigated, more than 35% of the impacting ions survive the surface collision in the cationic charge state.     

Nanosized metal deposits on titanium dioxide for augmenting gas-phase toluene photooxidation

The build-up of intermediate species on the surface of TiO₂ during gas-phase toluene (C₇H₈) photodegradation has been observed to deactivate the photocatalyst. Nanosized metallic deposits on the TiO₂ surface may enhance the photocatalytic process and improve photocatalyst performance. In this study, noble (Ag, Au) and platinum group (Pt, Pd, Rh) metals, at a nominal loading of 0.5 at.%, were deposited onto Degussa P25 TiO₂ to enhance photocatalyst performance and inhibit deactivation. Pd, Rh and Au deposits delayed photocatalyst deactivation by a factor of 2, while Pt deposits delayed photocatalyst deactivation by a factor of 20, when compared with neat TiO₂. Ag deposits did not improve photocatalyst activity. Metal deposit performance was related to the work function of each metal, however, the Pt finding suggested that these effects are not governed solely by this aspect, but factors such as deposit characteristics and/or thermal catalytic properties of the metals may be influential.     

IR spectroscopic studies of periodic columnar nanostructures of anodic titanium oxide

The experimental specimens consisted of periodic columnar nanostructures of anodic titanium oxide (average dimension≈60 nm) that were produced by anodic oxidation of the two-layer thin-film composition Ti−Al in a solution of oxalic acid that was followed by vacuum annealing. The structures formed were studied by electron microscopy and reflection IR spectroscopy. It is found that the nanodimensional columns consist predominantly of quasiamorphous Ti dioxide in the form of rutile and anatase with minimum inclusions of Ti₂O₃ and TiO. Vacuum annealing decreases the content of TiO₂ and increases that of Ti₂O₃ and TiO in the oxide columns. These changes characterize dissolution of oxygen from the composition of the columnar structures in a residual film of metallic Ti. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 200–204, March–April, 1998.     

The stabilization mechanism of titanium cluster

A systematic and comparative theoretical study on the stabilization mechanism of titanium cluster has been performed by selecting the clusters Ti_n (n=3, 4, 5, 7, 13, 15 and 19) as representatives in the framework of density-functional theory. For small clusters Ti_n (n=3, 4 and 5), the binding energy gain due to spin polarization is substantially larger than that due to structural distortion. For medium clusters Ti₁₃ and Ti₁₅, both have about the same contribution. For Ti_n (n=4, 5, 13 and 15), when the undistorted high symmetric structure with spin-polarization is changed into the lowest energy structure, the energy level spelling due to distortion fails to reverse the level order of occupied and unoccupied molecular orbital (MO) of two type spin states, the spin configuration remains unchanged. In spin restricted and undistorted high symmetric structure, d orbitals participate in the hybridization in MOs, usually by way of a less distorted manner, and weak bonds are formed. In contrast, d orbitals take part in the formation of MOs in the ground state structure, usually in a distorted manner, and strong covalent metallic bonds are formed.     

Self-inhibition of water dissociation on magnesium oxide surfaces

Hydroxylated MgO surfaces have been prepared by exposure to water vapour of MgO crystals at room temperature. High hydroxyl coverages were achieved on freshly cleaved surfaces. However, upon adsorption–desorption cycles of the hydroxyl adlayer, the ability of the MgO surfaces to dissociate water was seen to be dramatically inhibited. Reduced reactivities have also been observed on both air- and water-exposed MgO surfaces. This reactive behaviour is discussed in relation to the theoretical prediction that the MgO(100) face is not expected to dissociate water molecules.     

Collision-induced dissociation of hydrated adenosine monophosphate nucleotide ions: protection of the ion in water nanoclusters

Fragmentation of singly charged anions of adenosine 5'-monophosphate (AMP-) induced by collisions with neutral atoms (Ne, Na) has been studied at a collision energy of 50 keV. The experiments were performed with isolated AMP- as well as with AMP- anions nanosolvated in a cluster with a given number m of water molecules. In the first case, the dominant fragmentation channels concern the loss of adenine, PO3- and H2PO4-. In the latter, loss of water molecules becomes the dominating process, and the AMP- ion is fully protected when m is larger than approximately 13. The observed fragment distributions are well described with the model of an evaporative ensemble.     

Photoinduced dissociation reactions of silver fluoride cluster ions

Photoinduced dissociation in the ultraviolet region has been investigated for Ag _nF _n-1 ⁺ cluster ions. Photodissociation spectrum of Ag₂F⁺ in the energy of 3.8–5.6 eV exhibits several sharp bands corresponding to the transition to electronically excited states. In this dissociation, only the Ag₂ ⁺ ion was observed as a fragment ion. Theoretical calculation indicates that the parent Ag₂F⁺ ion has a linear Ag-F-Ag equilibrium geometries in the ground and excited states. Since conformational changes by excitation of bending vibration are necessary for the fragmentation of an F atom, this indicates that production of Ag₂ ⁺ from Ag₂F⁺ is a result of internal conversion and following conformational changes.     

Size-dependent reactivity of aluminum cluster cations toward water molecules

Using the autocorrelation of speckles in the deep Fresnel region is a novel approach to measuring surface parameters of a rough surface. In this letter, we construct a scanning system using a fibre-optic probe for detecting the speckle field with excellent resolution. By relating the autocorrelation function of the speckle intensity and the surface height with the Kirchhoff approximation theory, we realise the measurement of the surface parameters. Three parameters, i.e. the roughness w, the lateral correlation length ξ and roughness exponent α are extracted. We measure two sample surfaces in the experiment, and the results are consistent with those measured by atomic force microscope (AFM).