R. Rejoub

Electron-impact ionization of the simple alcohols

Absolute partial and total cross sections for electron-impact ionization of methanol, ethanol, and 1-propanol are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in most of the absolute cross sections is ±6%–8%. Significant discrepancies are seen between the only prior methanol partial cross section determination and this study but the majority of published total cross section measurements and calculations are in good agreement with this work.

Absolute partial cross sections for electron-impact ionization of SF6 from threshold to 1000 eV

Absolute partial cross sections for electron-impact ionization of SF6 are reported for electron energies from threshold to 1000 eV. The product ions are mass analysed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of SF5+, SF4+, SF3+, SF2+, (SF+ + SF42+), S+, F+, SF32+, SF22+ and SF2+ and for the total cross section, which is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for singly charged ions, except S+, is ±5%; that for S+ is ±8%. The uncertainty in the cross sections for doubly charged ions is ±12 to 15%. Data are also presented for formation of (SFn+, F+) ion pairs. Comparison is made with prior experiments and calculations.

Absolute cross sections for electron-impact ionization of N2O, H2S, and CS2 from threshold to 1000 eV

Absolute partial and total cross sections for electron-impact ionization of N2O, H2S, and CS2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of N2O+, N2+, NO+, N+, and O+ from N2O; for production of (H2S++HS++S+) and H+ from H2S; and for production of CS2+, S2+, CS+, S+, C+, and CS22+ from CS2. The total cross sections are obtained as the sum of these partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is ±6–8%. For all three targets the cross sections for production of lighter fragment ions are found to be greater than previously reported which is consistent with the presumption of incomplete collection of energetic ions in the earlier ...

Electron-impact ionization of NH3 and ND3

Absolute partial and total cross sections for electron-impact ionization of NH3 and ND3 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of (NH3++NH2++NH++N+), H+, H2+, and NH32+ from NH3 and for production of ND3+, ND2+, ND+, N+, D+, D2+, and ND32+ from ND3 and for the total cross sections which are obtained as the sum of these partial cross sections. Data are also presented for formation of (ND+,D+) and (N+,D+) ion pairs. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±6–8% while that for doubly charged ions is ±20%. It is observed that the isotopic composition of the ammonia target has no discernible effect upon the cross sections and that the part...

Charge transfer of keV O+ ions with CO and H2O

We report measurements of the absolute differential cross sections?(DCSs) for charge-transfer scattering of 0.5-5?keV O+ ions by CO and H2O at scattering angles between 0.04? and 2.9? in the laboratory frame. Estimated total charge-transfer cross sections, derived from these measurements, are compared with previously published data. Cross sections for both O+(4S) ground state and O+(2D, 2P) metastable ions are presented. In contrast to the results of several previous studies the internal energy of the O+ ions is found to have little effect on either the angular dependence of the DCSs or on the total cross sections.

Electron-impact ionization of the methyl halides

Absolute partial and total cross sections for electron-impact ionization of CH3F, CH3Cl, CH3Br, and CH3I are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of CHnF+, CHnCl+, CHnBr+, CHnI+, CHn+, F+, Cl+, Br+, I+, and H+, where n=0–3. Data are also reported for production of H2+, H3+, and doubly charged species at 100 eV. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±6%. It is observed that, although the Deutsch–Mark and the binary-encounter-Bethe theoretical formalisms are able to predict some features of the measured total cross sections, neither is consiste...

Absolute partial cross sections for electron-impact ionization of CF4 from threshold to 1000 eV

Absolute partial cross sections for electron-impact ionization of CF4 are reported for electron energies from threshold to 1000 eV. The product ions are mass-analysed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of CF3+, CF2+, (CF+ + CF32+), C+, F+ and CF22+ and for the total cross section which is obtained as the sum of these partial cross sections. The overall uncertainties in the absolute cross section values are ±5% to ±8%. Data are also presented for formation of (CF+, F+) and(CF2+, F+) ion pairs. Comparison is made with prior experiments and calculations.

Production of positive ion pairs by electron-impact ionization of CH4

Absolute partial cross sections for formation of (CH2+,H+), (CH+,H+), and (C+,H+) ion pairs resulting from electron-impact ionization of CH4 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector.

Comment on `Asymptotic behaviour of the total cross section for double ionization of helium-like ions by electrons'

Defrance et al (Defrance P, Kereselidze T M, Noselidze I L and Tzulukidze M F 2001b J. Phys. B: At. Mol. Opt. Phys. 34 4957-68; Defrance P, Kereselidze T, Noselidze I and Tzulukidze M 2001a 22nd Int. Conf. on Photonic, Electronic, and Atomic Collisions (Santa Fe, CA) (abstracts of contributed papers) p 315) have reported calculations of the electron-impact double-ionization cross section for helium that display a markedly different high-energy behaviour than do most of the published experimental data and they contend that new precise measurements are needed. The results presented here confirm the correctness of the more recent experimental data and indicate that revision of the theory is required.