Excitation of the Giant Resonance inC12by Inelastic Electron Scattering

The longitudinal and transverse form factors were determined separately as functions of the excitation energy from 15 to 40 MeV in the momentum-transfer range 0.75-1.56 ${\mathrm{F}}^{-1\mathrm{}}$. For some of the form-factor spectra the measurements were extended up to an excitation energy of 100 MeV and the results were compared with the quasielastic model presented by de Forest. The $q$ dependence of the experimental form factors for levels were compared with the predictions of the particle-hole model and with the intermediate-coupling model. We have then found the levels with the following excitation energies (MeV), spins, and parities: 18.1 ($1^{-}$), 18.6 ($3^{-}$), 19.6 ($4^{-}$), 20.0 ($2^{+}$), 20.6 ($3^{+}$), 21.6 ($3^{-}$), 22.0 ($1^{-}$), 22.7 ($1^{-}$), and 23.8 ($1^{-}$). We have also found new evidence of the possibility of the spin-isospin mode for the 22.7-MeV ($1^{-}$) excitation.