Mode Dependence in Vibrational Excitation of aCO2Molecule by Electron and Positron Impacts

We have found theoretically, for the first time, that vibrational excitations of a $\mathrm{CO}{}_2$ molecule by electron $\left(e^{-}\right)$ and positron $\left(e^{+}\right)$ impacts are strongly dependent on the charge of the projectile at impact energy below 6 eV. For the symmetric-stretching mode, the excitation cross section of $e^{-}$ impact is larger by 2 to 3 orders of magnitude than that of $e^{+}$ impact, while for bending and asymmetric-stretching modes the magnitude of both cross sections for $e^{-}$ and $e^{+}$ impacts is nearly comparable. These results are qualitatively confirmed experimentally, and are interpreted as the difference of interactions and incident $e^{-}$ or $e^{+}$wave functions.