Y Morioka

Photoionisation mass spectrometric study of acetylene in the VUV region

Photoionisation mass measurements on acetylene have been made between 1100 and 400 AA by using synchrotron radiation as a light source. Photoionisation efficiency curves are obtained for the molecular ion C2H2+ and also for fragment ions C2H+, C2+, CH2+ and CH+. To assign the structures of C2H2+, ab initio calculations have been performed for the excitation from the second (3 sigma g) and third (2 sigma u) occupied molecular orbitals. Two broad maxima at 930 and 810 AA between the first and second ionisation thresholds are assigned to the autoionisation from valence-type excited states. New Rydberg series (np pi u) converging to the second ionisation threshold were found. The appearance potentials of fragment ions by photoexcitation are given and discussed in terms of the heats of formation of molecular ions. For each of C2+ and CH+, two values of the appearance potential are obtained from a double-step structure. The maximum heat of formation of C2+ is estimated from the appearance potential to be 1980 kJ mole-1.

Absolute rate constant for the chemiluminescent reaction of atomic oxygen with nitric oxide

The absolute rate constant for light emission from the NO–O reaction has been determined, as a function of wavelength, by using a standard brightness source, which has a surface of uniform brightness. The spectral distribution measured between 0.4 and 1.4 μm is in good agreement with those of the previous studies except for a little difference in the near infrared region. The influence from NO–O3 chemiluminescence is demonstrated for atomic oxygen production from O2 discharges.

High resolution threshold photoelectron spectroscopy of rare gas dimers

Information on the structure of the ions of neon, argon, krypton and xenon dimers has been obtained using threshold photoelectron spectroscopy and synchrotron radiation under conditions of high resolution. Vibrational structure has been well resolved for the ground state of all these species thus allowing accurate values for the spectroscopic constants to be derived. Structure corresponding to excited states of the dimer ions dissociating to the 2P3/2,1/2 levels of the atomic ion have also been identified and their dissociation energies determined.

High-resolution VUV spectroscopic facility at the Photon Factory

A high-resolution spectroscopic facility, consisting of a 6.65-m vertical dispersion off-plane Eagle spectrograph/monochromator and a unique predisperser system of zero-dispersion type, has been designed and constructed at the Photon Factory. A description is given of design principle, optical system, mechanical arrangement, vacuum system, control system, and performance in the spectrograph mode. The resolving power was estimated from the separation between two closely lying lines of Ar I at ∼79 nm in the seventh order to be >2.5 × 105 —the highest resolving power ever demonstrated for this spectral region.

Ground and excited states of Xe+2 observed by high resolution threshold photoelectron spectroscopy of Xe2

Threshold photoelectron spectra of the xenon dimer have been observed with a resolution of 2 meV in the wavelength range 920–945 A and 1022–1112 A using the penetrating field technique and synchrotron radiation. Threshold photoelectron bands associated with transitions to the A2 Σ+1/2u, B2 Π3/2g, C2 Π3/2u, C2 Π1/2u, and D2 Σ+1/2g states of Xe+2 have been identified. Vibrational structure associated with the C2 Π1/2u state has been observed for the first time and a new value of the D2 Σ+1/2g state ionization potential is reported.

A high‐flux 3‐M normal incidence monochromator at beamline 20A of the Photon Factory

A high‐flux 3‐m normal incidence monochromator (3‐m NIM) has been installed at beam line 20A of the Photon Factory. The 3‐m NIM can supply a high photon flux in the wavelength region 30–200 nm, primarily because of a large horizontal acceptance angle of 28 mrad for the synchrotron radiation (SR) beam from bending magnet 20. The photon flux of the 3‐m NIM was estimated to be ≊1012 photons/s with Δλ≊0.1 nm at ≊50 nm by measuring the photoemission current from a gold‐coated surface. The resolving power with a 2400 grooves/mm grating was found to be greater than 25 000 at 90 nm from the autoionization profile of the Xe nd’ states converging to Xe+ 2P1/2.

Performance of the 6VOPE high resolution VUV spectroscopic facility in the photoelectric detection mode

Absorption measurements of krypton gas have been carried out to evaluate the performance of the high resolution spectroscopic facility 6VOPE using photoelectric detection. The 6VOPE is designed to make use of high spectral orders and consists of a 6.65-m vertical dispersion off-plane Eagle spectrograph/monochromator and a zero-dispersion tandem grating predisperser system. Focal plane scanning is used to achieve high resolving power (>==10(5)) for photoelectric measurements in the 40-200-nm range. A description is given of the mechanism and performance of the 6VOPE in the focal plane scanning mode. The resolving power and focused stray light level at ~88 nm are estimated experimentally to be greater, similar1.5 x 10(5) and less, similar 3%, respectively. Contrary to the usual experience the focused stray light of the 6VOPE is composed entirely of VUV light scattered from the main grating.

Vibrational structure of the N+2 ground state observed by threshold photoelectron spectroscopy

The long vibrational progression of the ground state of N+2 was observed in a high resolution threshold photoelectron spectrum obtained using the penetrating field technique and synchrotron radiation. Vibrational states were observed up to v′=67 for the first time and the final vibrational level was deduced to be v′=77 from extrapolation. The complete molecular constants of this state were obtained and the entire potential curve was then drawn.

Vibrational structure of the ground state of Ar2+ by the threshold photoelectron-ion coincidence technique

The coincidence between threshold electrons and ions from Ar2+ was taken to separate the monomer ions and the dimer ions between 790 and 855 AA using synchrotron radiation as a light source. The vibrational structure of the ground state of the Ar2+ ion was clearly observed. The energy of the Ar2+ ionic state is determined to be 116 432+317.2( nu +1/2)-2.5( nu +1/2)2(cm-1) from the zero vibrational state of Ar2.

Appearance of interatomic Coulombic decay in Ar, Kr, and Xe homonuclear dimers

Interatomic Coulombic decay (ICD) is observed in the rare gas homonuclear dimers Ar2, Kr2, and Xe2 with photoion spectroscopy techniques. Inner valence ionization of the outer ns shell of these systems is known to create a metastable state that dissociates to form a ground state ion and a neutral excited fragment. Inner valence ionization to form ns satellite states leads to similar dissociations, but the neutral fragment gets all the more excited as the internal energy of the ns satellite state increases. When enough excitation energy is transferred to reach the ionization potential, ICD occurs. ICD threshold is observed to coincide with the position of the A+A+ ground state in the Franck-Condon region.