Shinji Tomoda

Ionization energies and hydrogen-bond strength of the water clusters

Abstract The first vertical ionization energies of the water clusters (H2O)n for n = 1–8 have been evaluated from ab initio SCF MO calculations. The values obtained for n = 5 and 8 are in reasonable agreement with the experimental values of ice. The stability of the clusters is examined in terms of the hydrogen-bond strength per bond (Bh).

Direct evidence for terrace bending from He beam scattering on Pt(997)

He-nozzle beams (λ = 0.56 AA, S = (λ2/Δλ2)12 ≃ 17) were scattered on a stepped Pt(997) surface. Diffraction peaks up to the 6th order are clearly resolved. For incident angles θi < 65°, the diffraction patterns are very similar to the patterns obtained by light scattering on echellette gratings. An elementary model based upon this analogy fits the results fairly well. The deviations observed for glancng angles of incidence are interpreted as an evidence for an upward bending of the interaction potential on the terrace in the vicinity of the downward step.

Electronic and molecular structure of the water dimer cation. A theoretical study

Abstract Ab initio configuration-interaction calculations of the water dimer cation were performed with a basis set including polarization functions. The ground and first excited state are energetically close to each other and have I 2 A″ and 1 2 A, symmetries, with bent and linear H…OH equilibrium geometrics, respectively.

Photoelectron spectroscopic study of simple hydrogen-bonded dimers. I. Supersonic nozzle beam photoelectron spectrometer and the formic-acid dimer

Abstract In this paper we describe several characteristics of our supersonic nozzle beam photoelectron spectrometer recently constructed for studying hydrogen-bonded dimers in the gas phase by HeI (58.4 nm) radiation. Using this photoelectron apparatus, we have reinvestigated the HeI photoelectron spectrum of the formic-acid dimer (HCOOH) 2 which is well known as a fairly strong doubly hydrogen-bonded dimer. It was found that the (HCOOH) 2 spectrum deduced here from the spectrum of the monomer—dimer mixture considerably differs from that reported by Carnovale et al. in the region beyond 16.5 eV. New spectral assignments are given for four ionization bands beyond 16.5 eV. It is also indicated that the lower bound of the dissociation energy of (HCOOH) 2 + is estimated to be 1.0 ± 0.1 eV from the threshold of the dimer band (11.0 eV) obtained in this experiment. This value is considerably smaller than the value of 1.7 ± 0.2 eV recently reported for the water dimer cation (H 2 O) 2 + .

Refraction effects in atom scattering from stepped surfaces

Abstract He and H2 beams striking a Pt(997) surfce in step-down incidence give rise to a “terrace rainbow” diffraction pattern indicative of specular reflection from flat terraces. The rainbow angle, however, does not coincide with the “terrace specular” direction but shows a shift that increases with angle of incidence, much like a “refraction shift” caused by the attractive potential. A quantative analysis in these terms using the hard corrugated wall plus attractive tail (HCWT) model revealed a difference between He and H2 beams. For He, the model was able to reproduce the experimental intensities adequately over a wide range of incident energies and angles. For H2, however, the same was not true and we conclude that the HCWT model does not adequately represent the H2-metal interaction. Some reasons for this difference are discussed.

Scattering of potassium atomic beams from various cleaved surfaces

Abstract Scattering of potassium atomic beams from cleaved surfaces of LiF, KCl and mica were studied. The observed spatial distributions follow the cosine distribution in most cases. At large incident angles the distributions from LiF and KCl deviate from the cosine and show apparent backscatterings. A simple model is proposed to interpret the backscattering in terms of macroscopic roughness of cleaved surfaces. The sticking coefficient S ( t ) is defined and the mass balance between the incident and outgoing atoms is examined. Mass balance holds within the limits of errors on the surfaces of LiF and KCl at temperatures above 400 K. On a mica surface deposition of potassium atoms is observed even at temperatures higher than room temperature. It is shown from the change of the sticking coefficient that the deposition does not proceed linearly in the initial period.

Kinetics of the Deposition of Potassium Atoms on a Mica Surface

In the study of the process of the deposition of potassium atoms on a mica surface by means of molecular beams, the phenomenon that the sticking coefficient changes with the exposure time and has a minimum at room temperature was observed. To interpret this phenomenon, simultaneous rate equations of adsorption were proposed and it was found that the sticking coefficient is expressed by S=1-\frac{N}{I}∑i=1∞\frac{\theta_{i}}{\tau_{i}}. The sticking coefficient curve having a minimum as observed in the experiment can be produced from the solutions of the equations related to the BET model. If the surface migration of adatoms is taken into account, the minimum of the theoretical sticking coefficient curves becomes less deep. If b≡N/Iτ2>1 the sticking coefficient curve monotonically tends to zero as observed in the experiment at higher temperature.