  The first measurement of the three-body photodisintegration of
longitudinally-polarized ^3He with a circularly-polarized \gamma-ray beam was
carried out at the High Intensity \gamma-ray Source (HI\gamma S) facility
located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent
double-differential cross sections and the contributions from the three-body
photodisintegration to the ^3He GDH integrand are presented and compared with
state-of-the-art three-body calculations at the incident photon energies of
12.8 and 14.7 MeV. The data reveal the importance of including the Coulomb
interaction between protons in three-body calculations.
