Low-energy electron impact investigation of the triplet states of cyclopentanone and cyclohexanone

The angle-resolved electron energy-loss spectra of cyclopentanone and cyclohexanone have been measured at an electron energy of 5 eV above the threshold and at several scattering angles of 0-90 degrees. Five triplet bands together with four singlet bands have been newly observed. INDO/S CI calculations have also been performed for the spectral assignments. The singlet bands have been assigned to S₁(n, π^*) and ¹n → 3l(l = s, p, and d) transitions, and the triplet bands have been assigned to T₁(n, π^*), T₂(π, π^*), and ³n → 3l transitions from the comparison with the VUV absorption spectra of the cyclic ketones and the electron energy-loss spectra of acetone, which were reported earlier, and the calculated transition energies.