T. Takayanagi

Dissociation dynamics of CH+4 core ion in the 2A1 state

Threshold‐photoelectron photoion coincidence (TPEPICO) spectra of CH4 have been observed with synchrotron radiation at the excitation to the 2A1 (ν1=0−3) ionic states as well as to the 4pt2 Rydberg (ν1=0−4) states. In all the TPEPICO spectra observed, the CH+3 band shape was almost rectangular, which suggests that the translational and internal energy distributions of CH+3 are very narrow. The total kinetic energy releases (KERs) have been estimated from the CH+3 band shape. As a result, it was found that the CH+3 species were in an electronically excited state. There was a narrow distribution of the total KERs and similarity in the TPEPICO CH+3 band shapes between the spectra at the 2A1 ionic state and the 4pt2 Rydberg state excitations, which led to the conclusion that the Rydberg electron is just a spectator and the dissociation of the core ion plays an important role in dissociation through the 4pt2 Rydberg state. Similar results have also been obtained for CH+2 and CH+ productions. However, on the ot...

Electron impact ionization of O+, S+ and S2+ ions

Absolute cross sections for electron impact single ionization of O + , S + and S 2+ ions have been measured at an electron impact energy range from below threshold to 1000 eV, using the crossed beam technique. The measured cross sections for O + ions are reproduced quite well with the semiempirical Lotz formula over the whole energy range investigated. The measured cross sections for S + and S 2+ ions show a more rapid rise from the threshold to their peak than those expected from the Lotz formula. For S 2+ ions, another small bump beginning at 120 eV is observed, where no level exists that may contribute to any direct or indirect ionization processes.

Electron Impact Ionization of C + , N + and P + Ions

Absolute cross sections for electron impact ionization of C + , N + and P + ions have been measured for electron energies from threshold up to 1000 eV, using the crossed beam technique. The measured cross sections for both C + and N + ions are in good agreement with the semiempirical Lotz formula over the whole energy range investigated, and also with those previously reported except for near threshold. The results for P + ions show a more rapid rise from the threshold and larger values around the peak than those calculated with the Lotz formula.

Experimental observation of the F2 VUV laser levels

The f 3 Pi g state of molecular fluorine, which is assumed to be the upper level of a VUV F2 laser at 157 nm, has been directly observed for the first time by high-resolution electron energy loss spectroscopy at low impact energies (less than about 30 eV) and large scattering angles. The new transitions consist of several vibrational components at 11.62, 11.75, 11.86 and 11.99 eV, and show every characteristic feature of spin-forbidden transitions.

Electron spectroscopy of doubly-excited helium-like ions

Ejected electrons from helium-like doubly-excited carbon and boron ions, produced by C6+ and B5+ with He collisions, were measured by the zero-degree electron spectroscopy technique. Electrons from configurations 21nl were observed in a wide energy range.

Electron impact ionization of F+, Ne+, Cl+ and Ar+ ions

The crossed ion-and-electron-beams technique has been used to measure the absolute cross sections for single ionization of F + , Ne + , Cl + and Ar + ions by electron impact, over the electron energy range from below threshold up to 1000 eV. For F + and Cl + ions, the present experiment has provided the first absolute ionization cross sections. The measured cross sections for F + and Ne + ions are well reproduced with the semiempirical Lotz formula over the energy range investigated. The results for Cl + and Ar + ions show more rapid rise from the threshold than the prediction of the Lotz formula, indicating the contribution of excitation-autoionization processes, and tend to be in good agreement with the Lotz formula at higher energies.

Measurements of Ionization Cross Sections of 4d-Electrons in Xenon by Electron Impact

Partial ionization cross sections for 4 d -electrons in xenon by electron impact have been measured by means of a combination of the electron-energy-loss spectroscopy and the Auger electron spectroscopy in the impact energy region from 70 eV to 4 keV. The cross sections increase with the impact energy rapidly from the threshold and display a sharp maximum, whose value is (17.0 ± 3.5) × 10 -18 cm 2 , around 120 eV impact energy, revealing an existence of a resonance. The cross sections arise again from a minimum at about 200 eV and exhibit a broad maximum of (14.5 ± 3.0) × 10 -18 cm 2 around 500 eV. Absolute scale of the cross section is determined using the generalized oscillator strengths for the 4 d -ionization, which are measured by the electron-energy-loss spectroscopy. Relative cross sections are measured as a function of the impact energy using an Auger line assigned to the N 5 O 2,3 O 2,3 ( 1 S 0 ) line. Experimental results are compared with a previous experimental result given by a different proc...

Electron-Impact Double Ionization of Ba^+

The first observation of resonant structures is reported in the double ionization cross section in Ba + as a function of electron-impact energy, which are attributable to the 4d-ionization and the 5s-ionization followed by the autoionization. A brief description of the experimental method and procedures is presented. A discussion is also presented to provide a solid foundation to the identificaticn of the indirect processes concerned. Experimental results are compared with tentative results of the calculation using the distorted-wave Born exchange approximation by Younger.

Giant resonances in double ionization of atomic ions

Experimental studies on giant resonances in heavy atoms and ions by electron impact, carried on in our laboratory at Sophia University, are described. Three topics are discussed; the first one is measurements of the double ionization cross sections of singly charged alkaline‐earth ions by means of the crossed electron‐ion beams experiment. The second topic is measurements of partial cross sections for the inner shell ionization of rare‐gas atoms by means of the Auger electron spectroscopy. The third one is measurements of partial cross sections for the outer s‐subshell ionization of rare‐gas atoms by means of the VUV spectroscopy. Experimental results are discussed in relation to the giant resonance effect.

Measurements of Cross Sections for Single and Double Ionization of Na+ and K+ by Electron Impact

Cross sections for single and double ionization of K + and Na + by electron impact have been measured as a function of electron energy from their respective threshold to approximately 1500 eV with the use of the electron-ion crossed-beam technique. The results for single ionization of Na + and K + are in good agreement with the previous crossed-beam data within the experimental uncertainties. Contributions from an autoionization and an L-shell direct ionization followed by autoionization (Auger effect) have been found in the results of single and double ionization cross sections for K + .