Akihiro Matsuo

Fragment ion-photon coincidence study of dissociative ionization accompanying light emission by electron impact on acetylene

Fragment ion-photon coincidence (FIPCO) spectra by 120 eV electron impact on acetylene, C2 H2 , have been observed. Correlated detection of CH(A-X) emission and H+ and C+ ions, as well as between the CH+ ion and its own emission, was observed and verified with the help of Monte Carlo simulation of the band shapes observed. The translational energy distribution of the H+ ion is determined to be 1000±150 K (0.13±0.02 eV). Those for CH+ and C+ are 0.25 and 0.15 eV, respectively; the former translational energy accompanies a Gaussian distribution with a full-width at half-maximum (FWHM) of 0.2 eV, whereas the latter FWHM is 0.15 eV. A strong C2 Hn + (n = 0,1) band is also observed in the FIPCO spectra and ascribed to dissociative processes following light emission from C2 H+ and C2 H2 + . Similar experiments have been carried out at 350 eV electron impact energy, to examine the dissociative processes accompanying the light emission caused by the ionization of a C1s electron. No significant difference is observed between the FIPCO spectra at 120 and 350 eV impact energy.

A new band of O+ observed in measurements of angle-resolved translational energy by electron impact on O2

Abstract The translational energy distribution of O + produced by electron impact on O 2 has been measured in a supersonic free jet. A new band was observed at 0.2 eV by detection of only the cations flying at a right angle to the jet. The intensity was strongest at 90° to the direction of the electron beam and the appearance energy was 19.4±0.5 eV. It is concluded, on the basis of Dunns selection rule, that the new band originates from the 3 Π u -Rydberg series converging to the B  2 Σ g − state of O 2 + .

TRANSLATIONAL ENERGY DISTRIBUTIONS OF EXCITED CH+ IONS PRODUCED BY ELECTRON IMPACT ON METHANE

Fragment ion-photon coincidence (FIPCO) spectra by controlled electron impact on methane have been observed. To identify the observed ions correlating with photons and to estimate their translational energy distributions, Monte Carlo calculations have been carried out. These results indicated that the ion correlates with its own A-X and - emissions in the FIPCO spectra. The translational energy of was 0.20 eV, whereas that of ) was described by a Boltzmann distribution of 1000 K.

Dissociative ionization accompanying emission by electron impact on N2O using fragment ion-photon coincidence (FIPCO) measurements

Abstract Fragment ion–photon coincidence (FIPCO) measurements by controlled electron impact on N 2 O have been carried out in order to investigate the dissociative ionization processes correlating with the emission in the 250–600 nm region. The FIPCO spectra showed a band of the N 2 + ion. Its band shape depended on a choice of the specific wavelength region used and varied according to the wavelength region correlated. Its translational energy distributions have been estimated by Monte Carlo simulation. There are four dissociative ionization processes producing the N 2 + ion. One of them was related to the N 2 + (B–X) emission, and the others were related to emission from highly excited N 2 O + ions. Their cross-sections were estimated as (3–60)×10 −19 cm 2 .

Fragment ion-photon coincidence (FIPCO) measurements by electron impact on ethylene and the Monte Carlo simulation of the band shape

Fragment ion-photon coincidence (FIPCO) spectra by controlled electron impact on ethylene have been observed. Several typical band shapes to be observed in the FIPCO spectra have been simulated by Monte Carlo calculations and interpreted on the basis of the lifetimes of light emission and dissociation and of the sequence of emission and dissociation. The correlations between the CH(A-X) emission and the H+, CH+ and CH2+ ions are observed and verified by the Monte Carlo simulation of the observed band shapes. The average translational energy is estimated to be 0.09 eV for H+, 0.35 eV for CH+ and 0.04 eV for CH2+. The branching ratios of their ions are also estimated to be 6.6:89.7:3.7 for H+:CH+:CH2+. On the basis of dissociation limits, the threshold energies in the CH(A-X) excitation function and the translational energies of their ions, it is concluded that the H+ and CH2+ ions are produced through sequential dissociations into CH(A)+CH2(X)+H+ and into CH(A)+CH2+(X)+H(n = 1) and that the CH+ ion is produced through direct dissociation into CH(A)+CH+(X)+H2(X).

Mass analysis of high-Rydberg fragments produced by electron impact on ethane by use of a pulsed-field-ionization technique

Abstract A new apparatus to analyze the mass of high-Rydberg (HR) species produced by electron impact has been developed with the help of a pulsed-field-ionization (PFI) technique and applied to ethane. The intensity distribution of the HR species produced from ethane agreed well with that of the corresponding ions when PFI was carried out on a delay time of 2.0 μs after excitation. The intensity distribution, however, changed with an increase of the delay time. These findings demonstrate that the core ion model holds for the dissociation of HR ethane and that the lifetimes of the HR species are different.