The energies of the triply excited n = 2 intrashell He− resonances 2s22p and 2s2p2 revisited

Using a recently constructed high-resolution crossed-beam apparatus consisting of a hemispherical electron monochromator and a quadrupole mass spectrometer, we have measured in detail the He+ ionization cross-section function in the electron energy range from 56–59 eV. By fitting the two structures corresponding to the presence of the two triply excited n = 2 intrashell He− resonances (2s22p)2P and (2s2p2)2D with the theoretical natural line shape, we have deduced that their energy positions lie at 57.06 ± 0.05 and 58.15 ± 0.05 eV, respectively. Between these two states, an additional previously unseen structure has been observed and tentatively linked to the doubly excited autoionizing (2s2)1S state of He. When comparing the presently deduced resonance energies with previous data, there is good agreement within the error bars with those experiments which used both a similar experimental technique to detect these states and a data analysis based on the Fano line shape. Experimental results using other methods to detect and characterize these states (electron scattering, electron excitation) appear to lie at slightly higher energies; nevertheless, the energy separation between the two states is the same for almost all experiments

Dissociative electron attachment to hydrogen

Using two different crossed-beams high-resolution electron attachment instruments (employing either a trochoidal electron monochromator or a hemispherical electron monochromator) we have determined the cross section curve for H [iopmath latex="$^-$"] - [/iopmath] production from H2 via the 4 eV resonance at two different temperatures. These relative partial cross sections have been calibrated by comparing present values for the 14 eV resonance with absolute total cross sections determined previously. Taking into account the experimental energy distribution and the rotational excitation and its influence on the cross section shape we obtain very good agreement with theoretical predictions in terms of both the shape and magnitude of this resonance peak

Ionization energy studies for ozone and OClO monomers and dimers

Electron impact ionization cross sections measured close to threshold are reported for both the monomers and dimers of ozone and OC1O using a new high resolution electron impact apparatus. The present appearance energies AE(O[sup +, sub 3]-/O[sub 3])=12.70±0.02 eV, AE (OC1O[sup +]/OC1O)= 10.55±0.02 and AE(C1O[sup +]/OC10 = 13.37±0.03 eV derived from the measured ionization cross sections are in excellent agreement with the vertical threshold values determined for these ions by high resolution PES and PIMS photoionization studies. The corresponding appearance energies determined for the dimer ions, 10.10±0.3 eV for (O[sub 3])[sup +, sub 2] and 9.87±0.2 eV for (OC1O)[sup +, sub 2], are both red shifted with respect to the monomer case. The bond energy (0.70-0.3+0.5) eV of (OC1O)[sup +, sub 2] estimated from these data is similar to that of other dimer ions, whereas the bond energy of (O[sub 3]-O[sup +, sub 3]) with (2.55-0.4+0.6) eV is rather large suggesting an unusual structure for the cationic ozone dimer ion. Based on quantum chemical calculations on various levels we are led to the conclusion that the ion produced by ionization of the ozone dimer is no longer a conventional dimer ion where the two monomer units are still present (as is the case for the OC1O system), but rather an ion of form O[sub 2]...O[sup +, sub 4] or a twisted ring structure of (O[sub 6])[sup +]

Appearance energies of hydrogen and deuterium cluster ions

Electron ionization cross sections for hydrogen and deuterium clusters have been measured near the threshold energy with a high-resolution electron impact ionization mass spectrometer. Appearance energies are reported for odd-sized H-n(+) and D-n(+) cluster ions for sizes n less than or equal to 11

Electron Impact Ionization of Edge Plasma Constituents

In order to understand and elucidate the role of the radiative and collisional processes in the plasma edge region of fusion reactors, it is essential to have available a detailed and quantitative knowledge on these elementary processes such as cross sections, reaction rate coefficients etc. Much effort has been recently devoted to the experimental determination of absolute partial and total electron impact ionization cross sections of molecules and radicals due to the ever increasing importance of these cross sections in the diagnostics of many applications such as low- and high-temperature plasma physics and chemistry, atmospheric physics and mass spectrometry. In addition supporting calculations have recently been developed in order to allow the analytic quantitative description of these cross section functions for modelling codes using a novel approach to the determination of electron induced appearance energies. In this review we will therefore discuss (i) experimental studies on electron impact ionisation of neutral molecules and electron impact ionisation of molecular ions including the measurement of ionization cross sections and appearance energies and the determination of kinetic energy release distribution for dissociative ionization and (ii) the theoretical determination of electron impact ionisation cross sections for the single ionisation of molecules and the multiple ionisation of atoms