  The band dispersion of the two highest occupied molecular orbital
(HOMO)-derived bands in thin crystalline Pentacene films grown on Bi(001) was
determined by photoemission spectroscopy. Compared to first-principles
calculations our data show a significantly smaller band width and a much larger
band separation indicating that the molecular interactions are weaker than
predicted by theory--a direct contradiction to previous reports by Kakuta et
al. [Phys. Rev. Lett. 98, 247601 (2007)]. The effective hole mass m* at M-bar
is found to be anisotropic and larger than theoretically predicted. Comparison
of m* to field effect mobility measurements shows that the band structure has a
strong influence on the mobility even at room temperature where we estimate the
scattering rate to be tau ~3 fs.
