Tomohiko Hirooka

Photoelectron spectroscopy of naphthacene crystal in the vacuum ultraviolet region

Abstract The energy distribution curves of the photoelectrons emitted from naphthacene (C 18 H 12 ) crystal in the vacuum ultraviolet region were measured by an ac modulated retarding potential method. The peaks in the curves, 5.8 3 , 7.2 8 , 8.2 9 , 8.7 0 and 9.4 0 eV, are considered to be associated with the valence bands of the naphthacene crystal.

Photoemission from compounds containing benzene, naphthalene and anthracene ring systems

Abstract Photoemission measurements in the vacuum ultraviolet region from organic compounds, which contain benzene, naphthalene, anthracene and pyridine ring systems, were carried out. The change in the spectra upon condensation is discussed in terms of polarization energy.

Electron emission from surfaces of alkali halides under the impact of metastable helium and neon atoms

Abstract Energy distributions of the electrons ejected from the evaporated film surfaces of LiF, LiCl, LiBr, NaF and NaCl by the impact of metastable He and Ne atoms have been measured. The observed distribution curves have two distinct structures: one peak is identified as the valence band structure caused by Penning ionization, while the other peak is ascribed to scattered electrons. The positions of the valence band peaks are shifted to lower ionization energy from the corresponding photoelectron peaks (by 0.1–1.5 eV depending on the substance). In contrast to the photoelectron spectra, the structure attributable to conduction bands appears only very weakly. The relative intensity of the peak caused by scattered electrons is either strong or weak depending on the combination of the metastable atom and the sample. The interpretation of this observation is that the scattered electron peak is enhanced when the energy of the metastable atom exceeds twice the band gap energy, i.e. when the electron—electron scattering of Penning electrons in the solid is feasible.

Electron emission from naphthacene crystal due to the impact of argon and krypton metastable atoms

Abstract Energy distributions of electrons emitted from polycrystalline naphthacene due to the impact of metastable argon or krypton atoms were measured. The energy distribution peaks, except for large peaks appearing near zero eV, correspond to the kinetic energies estimated from photoelectron spectra on the assumption that the excitation energies of the metastable atoms are transferred to the electrons in the valence bands. The results are interpreted as the occurrence of Penning ionization (Auger de-excitation) on the naphthacene surface.

Observation of molecular reorientation on evaporated biphenyl film surface by penning ionization electron spectroscopy

Abstract Kinetic energy distributions or electrons ejected by impact of Ne∗(3P2,o) atoms from biphenyl films deposited on copper at 109 and 170 K were measured. The π4,π5 band in the 109 K spectrum was much higher than that in the 170 K spectrum, but upon annealing at 170 K became identical with the 170 K spectrum. This is interpreted as a transition, amorphous to polycrystalline, on the surface.

Orientation of benzene molecules adsorbed on graphite as studied by penning ionization electron spectroscopy

Kinetic energy distributions of the electrons ejected by impact of He(2 3S) atoms from benzene adsorbed on graphite (0001) plane at 100–140 K were measured. The intensities of the benzene σ bands relative to its π bands increased gradually with benzene exposure. The spectra indicate that at one-monolayer coverage the benzene molecules are nearly parallel to the substrate plane but the molecules on the top surface of multiple layers have large tilt angles with respect to the substrate plane.

Electron emission from crystal surfaces of condensed aromatics under the impact of metastable rare gas atoms

Abstract Energy distributions of electrons ejected from polycrystalline surfaces of naphthacene, perylene and coronene by the impact of metastable He * , Ne * and Ar * atoms have been measured. Two types of peaks, which are similar to the “non-moving” and “moving” structures in photoelectron spectra, are observed in each spectrum. The non-moving structures (ca. 1 eV) for perylene and coronene are similar to those in the photoelectron spectra, whereas the relative intensities of the two non-moving structures for naphthacene (0.6 and 1.7 eV) are remarkably different from the corresponding structures in the photoelectron spectrum. The peak positions (but not necessarily their intensities and widths) for the moving structures for all the samples (> 2 eV) agree with those of the corresponding photoelectron spectra. The origin of these moving structures is ascribed to Penning ionization on the solid surface.

Electrical conductivity, photoemission and absorption spectrum of tetraselenonaphthacene, C18H8Se4

Abstract The electrical conductivity, the photoemission and the absorption spectrum of tetraselenonaphthacene (TSN) evaporated film were studied. The conductivity of TSN film in a vacuum of 1.6 × 10−8 torr was 7.7 × 10−7 Ω−1 cm−1. When the film was exposed to air at atmospheric pressure, the value of the conductivity was found to be 1.1 × 10−4 Ω−1 cm−1. The ionization potential of the film estimated from its electron spectroscopy energy distribution curve was 4.45 eV. The absorption band at 15 400 cm−1 was insensitive to the pressure; on the contrary the band at 11 900 cm−1 showed a large red-shift at the rate of 120 cm−1/kbar. The remarkable difference in the pressure shift of the absorption bands in TSN film may arise from the Davydov splitting.

Microwave spectrum of propylene: Direct determination of the internal rotation splitting for the CH2DCHCH2 species

Abstract The microwave spectrum of a deuterated species of propylene, CH 2 DCHCH 2 , was investigated. Some of the 2 ← 1 transitions of the first-excited torsional state of the asymmetric form showed unusually large splittings and anomalous Stark effects. This observation was accounted for by an accidental degeneracy of the two J = 1 states, which were coupled by the tunnel effect and pushed away from each other. By analyzing the spectrum, the splitting due to the internal rotation was determined to be 19.3 and 768–795 Mc/sec for the ground and the first-excited states, respectively.

Orientation of pyridine molecules adsorbed on silver surface as studied by penning ionization electron spectroscopy

Abstract Kinetic energy distributions and yields of electrons ejected by impact of He (2 3 S) atoms from pyridine adsorbed on silver have been measured. The intensities of the peaks assigned to the n and π 3 bands of pyridine increase gradually with pyridine exposure from 1.2 L to ~ 50 L. The orbital energies of the π 1 , and π 2 peaks for 1.2 L exposure were observed to be about 0.5 eV higher than those for several tens of L and for gas-phase pyridine. These Penning spectra were interpreted as that at monolayer coverage ( ~ 1.2 L) pyridine molecules were chemisorbed with high inclination on the silver surface with N-Ag bonding and that they were oriented randomly at much higher exposures.