Total Single Ionization Cross Section Research Articles

Electron impact ionization of the SO2 molecule

We report measurements of the absolute cross sections for the electron-impact ionization of SO2 from threshold to 200 eV. Absolute cross sections for the formation of the SO+2 parent ions and of the SO+, S+, O+, and O+2 fragment ions were obtained independently in two different laboratories using two different experimental techniques with uncertainties ranging from ±18% to ±25%. The level of agreement between the absolute cross sections (at 70 eV) obtained by the two techniques ranges from about 10% for SO+2 and SO+ to 20% for (S++O+2) and O+, which in all cases is well within the combined error margins of the two measurements. The high resolution capability of the mass spectrometer employed in one experiment enabled the separation of the S+ and O+2 fragment ions, which are separated by only 0.017 76 atomic mass units (amu), for the first time. The single positive ion formation is the dominant process for all observed product ions. The total single SO2 ionization cross section obtained by the two techniques agreed to within 8%. A comparison of the experimentally determined total SO2 single ionization cross sections with calculated cross sections based on a modified additivity rule revealed agreement to within 20%.

Electron-impact ionization of the SO free radical

We studied the electron-impact ionization of the SO free radical using the fast-neutral-beam technique. Absolute cross sections were measured for the formation of the SO+ parent ion as well as for the S+ and O+ fragment ions from threshold to 200 eV. At 70 eV, cross section values of 3.25±0.50×10−20 m2 (SO+), 1.32±0.23×10−20 m2 (S+), and 0.45±0.08×10−20 m2 (O+) were obtained. We found little evidence of the presence of vibrationally excited SO radicals in the incident target beams and only negligible contributions to the measured ion signal from excited SO radicals in Rydberg and/or metastable states were observed. The only significant pathway contributing to the formation of the observed SO+, S+, and O+ ions is the single positive ion formation. The measured partial ionization cross sections were combined to yield the absolute total single ionization cross section of SO which was compared to calculations using a recently introduced modified additivity rule. The agreement between measured and calculated cross sections was found to be very good.

Electron Impact Ionization and Fragmentation of Metal‐Organic Compounds Used in Plasma Assisted Thin Film Deposition Techniques

AbstractMeasurements of the total and selected partial cross sections for the electron impact ionization of cyclopentadienyltrimethylplatinium (C5H5)Pt(CH3)3 [CpPtMe3], bismethylcyclopentadienylruthenium (CH3C5H4)2Ru [(MeCp)2Ru], and bismethylcyclopentadienylferrum (CH3C5H4)2Fe [(MeCp)2Fe] in the energy range from threshold up to 90 eV are presented. A double focussing mass spectrometer with an improved ion extraction system to avoid the discrimination of fragment ions with excess energy was used. The following values for the total single ionization cross sections σ at an impact energy of 70 eV and for the ionization energies (EI) were determined: σ = (13.7 ± 2.5) 10−16 cm2, EI = 7.6 ± 0.5 eV [CpPtMe3], σ = (23.2 ± 4.2) × 10−16 cm2, EI = 7.5 ± 0.5 eV [(MeCp)2Ru], σ = (20.2 ± 3.6) × 10−16 cm2, EI = 8.1 ± 0.5 eV [(MeCp)2Fe]. The results are compared with known mass spectra of the Pt‐ and Fe‐compound. Schemes for the fragmentation and ion formation processes in the ion source are discussed. The fragment ion composition as a function of the ion source temperature was investigated. The production rate of pure metal ions is small. The measured total single ionization cross sections when compared with calculations using two additivity rules were found to be lower than the calculated values.

Measured and calculated absolute total cross-sections for the single ionization of CF x and NF x by electron impact

Various additivity rules and the Deutsch—Märk (DM) formalism have been used to calculate total absolute electron-impact cross-sections for single ionization of the CF x ( x = 1–3) free radicals, the NF x ( x = 1,2) free radicals and the NF 3 molecule. A comparison is made with experimentally determined total single ionization cross-sections which have been obtained from recently measured absolute partial ionization cross-sections for the parent and dissociative ionization of these species. The overall best agreement between the measured and the calculated cross-sections in terms of the absolute values, the shapes and the cross-section ordering was obtained using a recently proposed “new” additivity rule. Common trends and tendencies in the ionization cross-sections within each class of targets, CF x and NF x , and between the two target families CF x and NF x are highlighted and a comparison will be made with the previously measured and calculated ionization cross-sections for the SiF x ( x = 1–3) free radicals.

Ionization of alkali-metal atoms by He+ impact

The total single ionization cross sections of alkali-metal atoms (Li, Na, K, Rb, and Cs) have been calculated in the binary-encounter approximation (BEA) using the Hartree–Fock velocity distribution function for the bound electron. The calculated cross sections are compared with the experimental data. The BEA results agree with the observations to within a factor of 2–3.