  The results of inelastic neutron scattering provide a solution for the
crystal field level scheme in PrOs4Sb12 in which the ground state in the cubic
crystal field potential of Th symmetry is a Gamma_1 singlet. The conduction
electron mass enhancement is consistent with inelastic exchange scattering, and
we propose that inelastic quadrupolar, or aspherical Coulomb, scattering is
responsible for enhancing the superconducting transition temperature. PrOs4Sb12
appears to be the first compound in which aspherical Coulomb scattering is
strong enough to overcome magnetic pair-breaking and increase Tc.
