We present calculations of spin-relaxation rates of alkali-metal atoms due
to the spin-axis interaction acting in binary collisions between the atoms.
We show that for the high-temperature conditions of interest here, the spi
n-relaxation rates calculated with classical-path trajectories are nearly t
he same as those calculated with the distorted-wave Born approximation. We
compare these calculations to recent experiments that used magnetic decoupl
ing to isolate spin relaxation clue to binary collisions from that due to t
he formation of triplet van der Waals molecules. The values of the spin-axi
s coupling coefficients deduced from measurements of binary collision rates
are consistent with those deduced from molecular decoupling experiments, a
nd follow a physically plausible scaling law for the spin-axis coupling coe
fficients.