Hi, I'm looking to numerically solve the rotational Schrodinger eqn. for a molecule which I'm happy to treat as an internally rigid body. The molecule will be in an external potential, so it's not a free rotor. Does anyone have any advice or references for an easy derivation of the K.E. operator? The rigid rotor page on Wikipedia has a derivation in terms of Euler angles, which I can maybe just about follow. Is this a good way to do this problem? Also, is the solution analytic for the general asymmetric top? If so- I'd like to form basis functions from the free rotor solutions. Thanks in advance for any help.