Irvin, With GSAS discrete D2 molecules can be modeled using rigid body constraints: http://www.ccp14.ac.uk/solution/gsas/rigid_bodies_gsas.html http://www.ccp14.ac.uk/ccp/web-mirrors/ian-swainson/fireside_fuide_to_ri gid_bodies.pdf
If the molecules are rotationally disordered you might try special form factors (like spherical shell one implemented in Fullprof) http://www.ill.fr/dif/Soft/fp/index.html In the extreme case of disorder you may also try to model continuous distribution of scattering density with Maximum Entropy Method (for example with Rietan+Prima) http://homepage.mac.com/fujioizumi/rietan/angle_dispersive/angle_dispers ive.html Cheers, Max
