  Using the multipole expansion we analyze photo induced reactions in an
ultra-cold atomic gas composed of identical neutral bosons. While the
Frank-Condon factor dominates the photo induced spin-flip reactions, we have
found that for frozen-spin process where the atomic spins are conserved the
reaction rate is governed by the monopole $r^2$ and the quadrupole terms.
Consequently, the dependence of the frozen-spin reaction rate on the photon
wave number $k$ acquires an extra $k^4$ factor in comparison to the spin-flip
process. Comparing the relative strength of the $r^2$ and quadrupole modes in
dimer photoassociation we predict that the mutual importance of these two modes
changes with temperature and scattering length.
