High-Resolution Inelastic Electron Scattering and the Isoscalar Nature of the M1 Transitions to the J^{ pi }=1^{+} State at E_{x}=5.846 MeV in^{208}Pb

The relative weight of proton and neutron spin-flip contributions to the M1 excitation of the recently discovered J/sup ..pi../ = 1/sup +/ state at E/sub x/ = 5.846 MeV has been determined by comparison of the momentum-transfer dependence of the measured electron-scattering form factor (q/sub eff/ = 0.44--1.59 fm/sup -1/) to results from a simple two-state model and from random-phase-approximation calculations using a spin- and spin-isospin--dependent effective separable interaction. The M1 transition is shown to be predominantly of isoscalar nature.