M4 excitations in 13C

Cross sections for the 9.50, 16.08, and 21.47 MeV M4 transitions in ¹³C have been measured by inelastic electron scattering. Isoscalar and isovector transition amplitudes were deduced by comparison with (π,π') and (p,p') data. In particular, the transition amplitudes obtained for the 9.50 MeV excitation give a remarkably consistent description of all existing measurements. A comparison was made with M4 transitions in other carbon isotopes, ¹²C and ¹⁴C. In each case, detailed shell model calculations accurately predict the energies, relative strengths, and isospin character of the observed M4 transitions. However, the shell model gives (e,e') M4 cross sections that exceed the data by a factor of 2.