Comparison of experimental and theoretical electron-impact-ionization triple-differential cross sections for ethane

We have recently examined electron-impact ionization of molecules that have one large atom at the center, surrounded by H nuclei (${\mathrm{H}}_2\mathrm{O}, \mathrm{N}{\mathrm{H}}_3, \mathrm{C}{\mathrm{H}}_4$). All of these molecules have ten electrons; however, they vary in their molecular symmetry. We found that the triple-differential cross sections (TDCSs) for the highest occupied molecular orbitals (HOMOs) were similar, as was the character of the HOMO orbitals which had a $p$-type “peanut” shape. In this work, we examine ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) which is a molecule that has two large atoms surrounded by H nuclei, so that its HOMO has a double-peanut shape. The experiment was performed using a coplanar symmetric geometry (equal final-state energies and angles). We find the TDCS for ethane is similar to the single-center molecules at higher energies, and is similar to a diatomic molecule at lower energies.

Figure 1

Dyson orbitals calculated for $\mathrm{N}{\mathrm{H}}_3, \mathrm{C}{\mathrm{H}}_4, {\mathrm{N}}_2$, and ${\mathrm{C}}_2{\mathrm{H}}_6$.

Figure 2

Coplanar symmetric geometry used for experimental measurements. See text for definition of the different variables.

Figure 3

Experimental TDCS for coplanar symmetric electron-impact ionization of $\mathrm{N}{\mathrm{H}}_3, \mathrm{C}{\mathrm{H}}_4, {\mathrm{N}}_2$, and ${\mathrm{C}}_2{\mathrm{H}}_6$ as a function of electron detection angle, for a series of outgoing electron energies. Both final-state electrons have equal energies as listed in the top row, and both are detected at equal angles as shown in Fig. 2. For each set of energies, the largest measured data have been normalized to unity.

Figure 4

Experimental and theoretical TDCS for electron-impact ionization of ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) as a function of electron detection angle, using the geometry in Fig. 2. For both experimental data and theoretical calculations, the largest cross sections have been normalized to unity for each set of energies. The theoretical curves are solid (red) is PA and dashed (blue) is OAMO.