Inelastic electron–dipole-molecule scattering at sub-milli-electron-volt energies: Possible role of dipole-supported states

Studies of collisions between Rydberg atoms with values of principal quantum number n in the range 100≲n≲400 and ${\mathrm{H}}_2$S and ${\mathrm{C}}_6$ ${\mathrm{H}}_5$ ${\mathrm{NO}}_2$ are reported. These targets were selected because they have very different dipole moments: 0.97 and 4.22 D, respectively. Analysis of the data using the essentially-free-electron model shows that at micro-electron-volt energies the cross sections for rotationally inelastic electron scattering by these targets have very different energy dependences. This difference suggests that, in the case of ${\mathrm{C}}_6$ ${\mathrm{H}}_5$ ${\mathrm{NO}}_2$, dipole-supported states might be important in the scattering. To examine this further, the data are compared with the results of calculations using a free-electron cross section that assumes the presence of dipole-supported states, and it is demonstrated that, with a reasonable choice of parameters, it is possible to reproduce the experimental observations.