Analytical Results for the Three-Body Radiative Attachment Rate Coefficient, with Application to the Positive Antihydrogen Ion H+

To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient α R A for producing the negative hydrogen ion H − or its antimatter equivalent, the positive antihydrogen ion H ¯ + , we found the analytic form for this integral. This procedure is useful for temperatures below 700 K, the region for which the production of H ¯ + has potential use as an intermediate stage in the cooling of antihydrogen to ultra-cold (sub-mK) temperatures for spectroscopic studies and probing the gravitational interaction of the anti-atom. Our results, utilizing a 50-term explicitly correlated exponential wave function, confirm our prior numerical results.

Nonadiabatic dynamics in energetic negative fluorine ions scattering from a Si(100) surface

The dependence of the negative-ion fractions on incident energy and angle is reported for 8.5-22.5 keV F(-) ions scattered from a Si(100) surface at a fixed scattering angle of 38°. The negative-ion fraction increases monotonically with incident velocity for specular scattering. In particular, the variation of the fraction with incident angle is bell shaped for a given incident energy. We interpret this variation using the incident-velocity effect at short distances where the yield of negative ions depends on the number of initial neutrals. It strongly indicates that at short distances, a dynamical equilibrium population is never achieved. This nonadiabatic feature is supported by simple calculations using modified rate equations.

Electronic Properties of Silicon - M Binary Clusters (M = C & Na)

Electronic properties of silicon-carbon and silicon-sodium binary clusters, produced by laser vaporization, were investigated by photoelectron spectroscopic or photoionization spectroscopic method. The photoelectron spectra of the C1Sim-1- clusters are similar to those of pure Sim- clusters in the peak positions and their envelopes, which is attributed to the similar electronic structure of Si and C atoms, leading to a similar geometry. In contrast, the similarity in the photoelectron spectra is not observed between Cn- and Cn-1Si1 clusters, which is attributed to a change in their geometry; from chain to ring.

The ionization energies (Ei) of the SinNam clusters (l≤n≤15) were determined from the threshold energy of their ionization efficiency curves. The clear parallelism between the ionization energy of SinNa and the electron affinity (EA) of Sin is found; there are three local minima at n=4, 7 and 10. This implies the facts that (1) the structure of the SinNa clusters keeps the frame of the corresponding Sin cluster unchanged and that (2) the parentage of singly occupied molecular orbital (SOMO) of SinNa is the LUMO of Sin. Furthermore, the EAs of SinNa (4≤n≤7) were determined from the threshold energy in the photoelectron spectra of SinNa". When the EAs of SinNa are compared with those of Sin, the EAs decrease at n=4-6, but the EA increases at n=7. The results of ab initio calculation show that the Na atom is bound by two Si atoms (bridge site) at n=4-6, whereas it is bound by one Si atom (apex site) at n=7.

Interaction of CsF with Multilayered Water

The interaction of CsF with multilayered water has been investigated with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy with HeI (UPS(HeI)). We have studied the emission from the ionization of H2O states 1b1, 3a1, and 1b2; of Cs5p and of F2p. We have prepared CsF-H2O interfaces, namely, CsF layers on thin films of multilayered water and vice versa; they were annealed between 80 and about 280 K. Up to about 100 K, a closed CsF layer can be deposited on H2O and vice versa; no interpenetration of the two components H2O and CsF could be observed. Above 110 K, CsF (H2O) layers deposited on thin H2O (CsF) films (stoichiometry CsF.1.5H2O) gradually transform into a mixed layer containing F, Cs, and H2O species. When annealing, H2O molecules can be detected up to 200 K from the mixed F-Cs-H2O layer (while for pure H2O desorption is essentially complete at 165 K); a water network is not formed under these conditions, and all H2O molecules are involved in bonding with Cs+ and F- ions. When CsF is deposited at 120 K on sufficiently thick water multilayers, full solvation of both F and Cs takes place, even for the species closest to the surface, as long as the stoichiometry remains CsF.(H2O)n with n > 3.