Electron collisions with methyl-substituted ethylenes: Cross section measurements and calculations for 2-methyl-2-butene and 2,3-dimethyl-2-butene

Electron collisions with X(CH3)4 molecules (X = C, Si, Ge)

Absolute grand-total cross sections (TCSs) for electron scattering from tetramethylmethane [C(CH₃)₄], tetramethylsilane [Si(CH₃)₄], and tetramethylgermane [Ge(CH₃)₄] molecules have been measured at electron-impact energies extending from around 0.5 to 300 eV in the linear electron-transmission experiment. The measured TCS energy dependences show very pronounced broad enhancement, peaking near 5.5 eV for Si(CH₃)₄ and Ge(CH₃)₄ molecules and around 6.5 eV for C(CH₃)₄. Additional weak structures are also located at higher electron energies. We attributed the TCS features to the resonant processes involved in the electron-molecule scattering. To examine the role of permethylation in the scattering, the measured TCS energy functions for X(CH₃)₄ compounds (X = C, Si, Ge) have been compared to the TCS curves for XH₄ molecules. Additionally, the integral elastic cross section (ECS) and ionization cross section (ICS) have been calculated from intermediate to high electron-impact energies using model methods. At energies above 50 eV, the sum of ECS and ICS for the investigated targets is in satisfactory agreement with the respective measured TCS. The computed ECS+ICS values can be used as rough estimation of TCS at energies above 300 eV.