Abstract
An optical pumping state-selection technique is employed for the measurement of intramultiplet mixing cross sections involving specified spin-orbit states of calcium 4s4p 3PJ0 atoms in collisions with H2 and D2. As was previously found for helium collisions, the J=2 to J'=1 cross sections are found to be the largest of the three possible downward transitions. However, differences in magnitude between the various J to J' cross sections are smaller than for helium. Moreover, the cross sections for the molecular targets are two to three times larger than for the same transitions with helium as the scattering partner. These differences are discussed in terms of the expected dynamics of fine-structure-changing transitions of 3P atoms with atomic and molecular scattering partners.