Enhanced Doppler coverage has been observed in the laser-induced optical pumping of lowdensity rubidium vapor in the absence of any buffer gas. Transient and steady-state measurements show that this enhancement arises from velocity-changing collisions {UCC s) of rubidium atoms with the walls of the cell containing the vapor. %a11-induced UCC s offer a possible mechanism for increasing the efficiency with which atomic and nuclear polarization may be produced with lasers.