Ab initio many-electron study for the low-lying states of the alkali hydride cations in the adiabatic representation Theoretical study of the electronic state and H-elimination reactions for solvated magnesium cluster ions

Photoionization thresholds for Gen (n⩽57) and Snn (n⩽41) are examined by laser photoionization with detection by reflectron time-of-flight mass spectrometry. Stimulated Raman anti-Stokes scattering of narrow bandwidth 193, 248, and 266 nm radiation is used to produce ionization light sources in the vacuum ultraviolet region (200–141 nm). A very similar size dependence of the ionization potentials (IPs) is found for germanium and tin clusters with fewer than 12 atoms, featuring a major maximum at n=10. The rather high IP of Ge10 compared with its neighbors is consistent with the results of a photodissociation study of Gen+. We also find a rapid decrease in the IPs for Gen between n=15 and 26, which is very similar to that for silicon clusters reported in our previous paper. On the other hand, the IPs of medium size Snn (n=15–41) clusters are found to decrease slowly without such a gap. The remarkable difference in the size dependence of the IPs for the Sin, Gen, and Snn clusters is discussed in relation to the existence of a structural transition in the medium-size Sin and Gen clusters.

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Multiphoton ionization and oxidation processes of ammoniated magnesium clusters are investigated by the multiphoton ionization method with an intense femtosecond laser. In the photoionization of mass-selected Mg+ (NH3)n, evaporation dominates at lower laser intensity, while the oxidation reaction to produce H-atom elimination products, MgNH2+ (NH3)m, becomes predominant at higher intensity. In addition to these fragment ions, doubly-charged ions are observed for n > or = 2 at the laser intensity higher than 10(12) W cm(-2). We also examined the femtosecond pump probe experiments for Mg+ (NH3)4 by monitoring these reaction products. The lifetime of the first excited state is determined as 0.8 ps from the temporal profile of MgNH2+ (NH3)m. On the other hand, the time profile of the evaporation products exhibits a bleaching of the absorption, which gives the recovery time of the initial state as 1.2 ps. Multiphoton excitation of Mg(NH3)n with the femtosecond laser at 800 nm gives doubly-charged ions with n > 3 in addition to singly-charged cluster ions and H-atom elimination products such as MgNH2+ (NH3)m. The absence of small doubly-charged ions is ascribed to a charge reduction reaction followed by Coulomb explosion. On the basis of these results, the dynamics of the solvation and oxidation reaction processes of Mg(NH3)n is discussed.

We examine the photoionization thresholds of Gen (n = 2 − 34) with a wide photon energy (5.0-8.6 eV) using a laser photoionization time-of-flight mass spectrometry. A high-output vacuum ultraviolet light generated with stimulated Raman scattering is used as the ionization light source in the energy above 6.0 eV. A characteristic size dependence of ionization potential (IP) with a maximum at n = 10 is found for clusters smaller than 22 atoms. The rather high IP of Ge 10 in comparison with its neighbors is consistent with the results on the photodissociation study of Ge + n . We also find that IPs decrease rapidly from n = 16 to 22, and then decrease at a much slower rate for larger clusters. These features in IPs are similar to those of Sin reported in our previous paper, except for the smaller IP gap of Gen at n ≈ 20. We discuss these results on IPs in relation to their electronic structure and stability.PACS. 36.40.Mr Spectroscopy and geometrical structure of clusters -71.24.+q Electronic structure of clusters and nanoparticles