Kinematic study of ${\mathrm{O}}^{-}$-ion formation from dissociative electron attachment to ${\mathrm{SO}}_2$

We report a complete kinematic study of ${\mathrm{O}}^{-}$-ion formation due to dissociative electron attachment to ${\mathrm{SO}}_2$ using the velocity slice imaging technique in the incident electron energy range over the resonances. Two resonances are observed at 5.2 and 7.5 eV, respectively. From the kinetic energy distribution, the two resonances are observed to have the same threshold energy, pointing to the fact that the two processes, giving rise to the two resonant peaks, have the same dissociation limit. From the angular distribution results we identified the involvement of an $A_1$ and a combination of $A_1+B_2$ temporary negative-ion state(s) for the first and second resonances, respectively.

Figure 1

Time-slice images of ${\mathrm{O}}^{-}$ ions at different incident electron energies around the first resonance. The arrows indicate the direction of the incident electron beam.

Figure 2

Time-slice images of ${\mathrm{O}}^{-}$ ions at different incident electron energies around the second resonance. The arrows indicate the direction of the incident electron beam.

Figure 3

The unweighted kinetic energy distribution of the ${\mathrm{O}}^{-}$ ions created due to interaction with different incident electron energies at the first resonance. The number of counts is normalized at the near zero eV peak value.

Figure 4

The unweighted kinetic energy distribution of the ${\mathrm{O}}^{-}$ ions created due to interaction with different incident electron energies at the second resonance. The number of counts is normalized at the near zero eV peak value.

Figure 5

The kinetic energy distribution at different ejection angles at 9.0-eV incident electron energy.

Figure 6

The most probable kinetic energy versus incident electron energy curve of ${\mathrm{O}}^{-}$ ions created due to the two-body breakup. The first two data points having almost the same energy as the third are not shown in the figure for a better fit. The linear fit for the data is also shown. The fitted line intersects the x-axis at 3.1 eV.

Figure 7

Angular distribution of the ${\mathrm{O}}^{-}$ ions having kinetic energy between 0 and 0.5 eV for all the five incident electron energies around the first resonance.

Figure 8

Fit to the angular distribution data of the ${\mathrm{O}}^{-}$ ions for 5.2-eV incident electron energy at the first resonance. The black solid line denotes the fit for the $A_1$ to $A_1$ transition, the blue dashed line denotes fit for the $A_1$ to $B_1$ transition, and the pink dash-dotted line denotes fit for the $A_1$ to $B_2$ transition.

Figure 9

Angular distribution of the ${\mathrm{O}}^{-}$ ions having kinetic energy between 0 and 0.2 eV for all the six incident electron energies around the second resonance.

Figure 10

Fit to the angular distribution data of the ${\mathrm{O}}^{-}$ ions for 7.5- and 9.0-eV incident electron energies around the second resonance. The black solid line denotes the fit for the $A_1$ to $A_1+B_2$ transition and the pink dashed line denotes fit for the $A_1$ to $B_2$ transition.