The relative phase of the longitudinal and transverse form factors of the 4.439-MeV $J^{\pi }=2^{+}$ state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been measured at $q_{\mathrm{eff}}=0.36\mathrm{} \mathrm{and} 0.46$ ${\mathrm{fm}}^{-1\mathrm{}}$. This phase was found to be negative, of the same sign given by Siegert's theorem in the long-wavelength limit. This measurement represents the first nuclear structure result derived through the ($e, e^{\prime }\gamma$) reaction.

• Received 21 August 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.26