The longitudinal and transverse structure functions of the ⁴H(e, e'p)³H reaction

⁴He(e, e'p)³H cross sections were measured in parallel kinematics for recoil momenta of 30, 90 and 190 MeV/c. For 30 and 90 MeV/c, the cross sections were also measured as a function of the momentum transfer between 0.30 and 0.83 GeV/c. A Rosenbluth decomposition of the cross sections was made, and experimental longitudinal and transverse spectral functions were derived. The longitudinal spectral function is quenched by about 40% relative to the transverse. After model-dependent corrections for final-state interactions, mesonic currents, and charge exchange scattering, the quenching remains at the level of {all equal to}20%. The spectral functions are compared to calculations employing realistic ⁴He wave functions. The longitudinal function is below the theoretical value; the transverse function is in agreement. The spectral function data reveal no significant q-dependence and imply an r.m.s. proton magnetic radius in ⁴He within a few percent of the free value.