  We consider spin-half fermionic atoms with isotropic Rashba spin-orbit
coupling in three directions. The interatomic potential is modeled by a square
well potential. We derive the analytic form of the asymptotic wave-functions at
short range of two fermions in the subspace of zero net momentum and zero total
angular momentum. We show that the spin-orbit coupling has perturbative effects
on the short range asymptotic behavior of the wave-functions away from
resonances. We argue that our conclusion should hold generally.
