Oscillations in electron impact cross sections of CO2between 3 and 5 eV

Excitation of the ground state vibrational modes of CO 2 has been studied in an electron impact experiment in the energy range 3-5 eV. A series of oscillations is observed in the excitation functions of the elastic and vibrational channels which was previously assumed to result from vibrational excitation of an intermediate negative ion (shape resonance). The oscillations were seen to move towards higher energies with increasing vibrational quantum number when observed in the symmetric stretch channel. This leads us to propose that the structure is due to an interference effect in the negative ion wavefunction (boomerang model).