Electron Scattering Cross Sections Results and Discussion: : Comparison of experimental cross sections with other measurements

3.2 Comparison of experimental cross sections with other measurements

For the CH₄ molecule, Zecca et al.¹⁶ measured total cross sections in the energy range 0.9 – 4000 eV and Garcia and Manero¹⁷ measured total cross sections in the energy range 400–5000 eV. For the comparison of these measurements with the present cross sections, their cross sections are normalized to the cross sections produced in the present experiment and shown in Figure 3.05. The total cross sections measured by Zecca et al.¹⁶ are in agreement with the present measurements only up to approximately 1000 eV, allowing for a 5% maximum deviation. At energies higher than 1500 eV, the total cross sections are reported in Reference [16] systematically lower than present measurements and showed a deviation of 27% at 4000 eV. Comparison with the measurements of Garcia and Manero¹⁷ indicates the highest deviation of 4% at 400 eV. Since the experimental errors in the present experiment and those of Garcia and Manero¹⁷ are, respectively, 4% and 3%, this deviation is within the experimental uncertainties. Therefore it is reasonable to conclude that the present cross sections of CH₄ are in good agreement with those of Garcia and Manero¹⁷ for the entire energy range. However, considering the 2 – 4 % experimental error in the work reported in Reference [16], the cross sections measured by Zecca et al.¹⁶ are significantly lower than the present measurements at energies higher than 1500 eV.

For the NH₃ molecule, Zecca, Karwasz, and Brusa ²¹ measured total cross sections in the 75 – 4000 eV energy range while Garcia and Manero²² measured the total cross sections in the energy range from 300 – 5000 eV. Both of these measurements have 3% experimental uncertainties. For the comparison of their results with the present measurements, their cross sections are normalized to the cross sections produced in the present experiment and shown in Figure 3.06. Considering the experimental errors, present total cross sections are in good agreement with those produced by Garcia and Manero²² with a maximum deviation of 4% at 2000 eV. Those total cross sections produced by Zecca, Karwasz, and Brusa ²¹ are in agreement with the present measurements only up to energies about 1250 eV. Above 1500 eV the total cross sections of Zecca, Karwasz, and Brusa ²¹ are systematically lower than the present work and showed a deviation of 26% at 4000 eV.

Figure 3.05 Cross sections produced in other laboratories normalized to present measurements for the CH₄ molecule. Straight solid line is the present experiment. The crosses and circles are, respectively, the measurements by Zecca et al.¹⁶ and Garcia and Manero¹⁷.

Figure 3.06 Cross sections produced in other laboratories normalized to present measurements for the NH₃ molecule. Straight solid line is the present experiment. The crosses and circles are, respectively, the measurements by Zecca et al.²¹ and Garcia and Manero²².

For the SiH₄ molecule, Zecca, Karwasz, and Brusa ²¹ measured total cross sections in the energy range 90 – 3500 eV with 2.5% experimental error. Sueoka, Mori, and Hamada²³ measured total cross sections in the energy range 90 – 400 eV with an experimental uncertainty of 6%. For comparison, their cross sections are normalized to the cross sections produced in the present experiment and shown in Figure 3.07. The present total cross sections are in good agreement with those produced by Zecca, Karwasz, and Brusa ²¹ for energies up to 1100 eV. At energies of 2000 eV and above their total cross sections are systematically lower than the present work and showed the highest deviation of 28% at 3500 eV. Lower energy measurements by Sueoka, Mori, and Hamada²³ are in fair agreement with the present work and showed a maximum deviation of 10% at 400 eV.

Figure 3.07 SiH₄ cross sections produced in other laboratories normalized to present measurements. Straight solid line is the present experiment. The crosses and circles are, respectively, the measurement by Zecca, Karwasz, and Brusa ²¹ and Sueoka, Mori, and Hamada²³.

From these total cross section comparisons with other experimental groups it is revealed that the present experimental measurements are in good agreement with those produced by Garcia and Manero^{17, 22} while total cross section measurements by Zecca et al.^{16, 21} are systematically lower than the present measurements at higher energies. It is important to mention here the present experimental measurements and the measurements by Garcia and Manero^{17, 22} are based on the linear transmission technique while the measurements by Zecca et al.^{16, 21} are based on the Ramsauer type technique. In the Ramsauer type experimental arrangement it is required to change both applied voltage and magnetic field for every energy. Inaccurate setup of both applied voltage and magnetic field may have caused the deviations of total cross sections at higher energies due to poor angular resolution and poor ability to distinguish inelastically scattered electrons.