Electron impact ionization of the SO2 molecule

Abstract

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%.

Partial differential cross sections for the ionization of the SO2 molecule by electron impact

“…Figure 2 shows a comparison of the direct ionization cross sections with the experimental data. [9][10][11] The present results are in good agreement with the experimental data of Basner et al 11 over the entire energy range (threshold to 200 eV) investigated in the experiment. However, near threshold a satisfactory agreement with all the experimental data [9][10][11] has been noticed.…”

“…23 In a similar way as for other molecules, we have calculated the partial ionization cross sections (PICS) of SO 2 by electron impact with energies varying from ionization threshold to 10 keV, by integration of PSDCS with respect to the energy loss W (or the secondary electron energy element P). Thus, the calculated results for PICS and the total single SO 2 ionization cross sections derived from the calculated PICS are in satisfactory agreement with the available theoretical data 7,11 and experimental data 5,[8][9][10][11] within the experimental uncertainties.…”

“…The experimental values of I i are taken from elsewhere. [5][6][7][8][9][10][11] For various molecules, the values of the mixing parameter P 0 were evaluated by Jain and Khare. 24 For the SO 2 molecule no such information is available and we have chosen it to be 100 eV as for CO 2 which is consistent with the procedure of Jain and Khare.…”

“…10 Their results disagreed by as much as a factor of 3.5. Very recently, Basner et al 11 reported absolute partial ionization cross sections for the SO 2 molecule by electron impact using two different techniques, i.e. the fast neutral beam technique at City College and the high resolution double-focusing mass spectrometer with a Nier-type electron impact ion source at Greifswald.…”

Electron-impact ionization cross sections of atmospheric molecules

“…11. Basner et al 32 actually report three distinct sets of cross sections, one set measured at the Universität Greifswald in Germany, another set measured at the City University of New York, and a semiempirical cross section based on an additivity rule by one of the authors at Greifswald. We present these three sets of cross sections individually in Fig.…”