We discuss the relaxation of a spin-polarized alkali-metal vapor due to the
electric-quadrupole interaction in (1)Sigma (+)(g) dimers, and present a m
odel that accurately describes the measured relaxation rates under a wide v
ariety of conditions. We use the model along with experimental results to d
educe the quadrupole interaction strength, atom-dimer chemical-exchange rea
ction rate, and the rate of reorientation of singlet dimers due to collisio
ns with the buffer gas.