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.     

Particle detectors for the future antiproton Paul trap of the ASACUSA experiment at CERN

Two detectors which will be used to commission a superconducting radiofrequency Paul trap for antiprotons, now being constructed at CERN and MPQ, are described. One is a microwire secondary electron emission monitor which will nondestructively measure the spatial profile of a low energy (E= 10?100 keV) antiproton beam. The other is a system of electromagnetic shower counters which will detect the secondary particles emerging from the antiproton annihilations occurring in the trap.     

Synthesis of Au–Pd bimetallic nanoparticles under energetic irradiation fields

Bimetallic Au–Pd nanoparticles were synthesized under high-energy irradiation fields (1.17 and 1.33 MeV γ-rays, 9 MeV electrons, and 1.6 GeV C ions) from solutions containing Au³⁺ and Pd²⁺ and cationic surfactant (sodium dodecyl sulfate). Particles synthesized by the irradiation were observed using conventional transmission electron microscope (TEM) and annular dark-field scanning transmission electron microscopy (ADF-STEM). The particles synthesized by γ-rays and C ion irradiation exhibit core–shell structure with a Au-core and a Pd-shell. The dependence of the size distribution of nanoparticles on the dose rate is discussed.     

Deposition of mechanically hard amorphous carbon nitride films from decomposition of BrCN. Effects of substrate cooling and pulsed rf-bias voltage

Mechanically hard amorphous carbon nitride films were formed by applying a combination of radio frequency (RF) bias voltage to the substrate and the chemical vapor deposition process using the decomposition reaction of BrCN with the microwave discharge flow of Ar. Cooling water was circulated inside the substrate stage. The maximum hardness was (17 ± 1) GPa for the film prepared under the negative RF bias voltage, −V_RF, of 30 V. This hardness was nearly twice that of the film prepared without cooling, suggesting that substrate cooling was effective for suppressing the relaxation of the internal stress of the film due to the temperature rise during the application of the RF bias voltage. Under the continuous operation of the RF bias voltage, films cannot be formed for −V_RF > 40 V because of the sputtering by the bombardment of energetic Ar⁺. Then, the RF bias voltage was applied with a pulsed operation. By using this operation films were prepared in the range of −V_RF = 40-100 V. The hardness, (36 ± 10) GPa, was obtained for the film obtained under the conditions of −V_RF = 100 V, the pulse period of 1000 s, and the pulse-on time of 800 s. The observed hardness scattered largely for the different observation points within this film; a single observation point in that film showed the maximum hardness of 46 GPa. According to the IR spectra of the films, the three-dimensional C-N network structure was developed.     

Two photon laser spectroscopy of antiprotonic helium atoms at CERN’s AD

The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths λ = 139.8–197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 10⁹. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results.     

Theoretical and experimental investigation on the electronic properties of the shuttlecock shaped and the double-decker structured metal phthalocyanines, MPc and M(Pc)2 (M = Sn and Pb)

The molecular geometries, electronic structures, and excitation energies of tin and lead phthalocyanine compounds, SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2), were investigated using the B3LYP method within a framework of density functional theory (DFT). The geometries of SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2) were optimized under C(4v), C(4v), D(4d), and D(4d) molecular symmetries, respectively. The excitation energies of these molecules were computed by the time-dependent DFT (TD-DFT) method. The calculated results for the excited states of three compounds other than the unknown Pb(Pc)(2) corresponded well with the experimental results of electronic absorption spectroscopy. The non-planar C(4v) molecular structure of SnPc and PbPc influences especially on the orbital energy of the HOMO-1 through mixing of the s-type atomic orbital of the central metal atom to the π system of the Pc ring in an anti-bonding way; however, the HOMO and the LUMO have little effect of the deviation from the planar structure because they have no contribution from the atomic orbital of the central metal. This orbital mixing pushes up the orbital energy of the HOMO-1, and reduces the energy of the metal-to-ligand charge transfer band of SnPc and PbPc. The calculated results also reproduced well the excitation profile of Sn(Pc)(2), which was quite different from that of SnPc. The strong interactions between the π-type orbitals of two Pc moieties altered the electronic structure resulting in the characteristic excitation profile of Sn(Pc)(2). In addition, this caused a reduction of about 0.8 eV in the ionization potential as compared to usual MPcs including SnPc, which was consistent with the experimental results.     

Measurement of a pauli and orbital paramagnetic state in bulk gold using x-ray magnetic circular dichroism spectroscopy

We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L(2) and L(3) edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3 × 10(-4) μB/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9 × 10(-6) for the 5d orbit. The induced paramagnetism in bulk Au is characterized by a large (≈ 30%) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles.