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                SEMINAR OF THE DYNAMICAL SYSTEMS GROUP
        Institute for Computational Sciences and Informatics
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          COLLISIONAL EXCITATION OF RIGID TOPS CONTAINING AN
                        INTERNAL ROTOR

                        Stephen L. Davis
        Chemistry Department, George Mason University

     Quantum mechanical inelastic cross sections have been
calculated for the simultaneous excitation of the overall and
internal rotation in a symmetric or asymmetric top containing an
internal rotor for collisions with a structureless particle.  The
model system employed was the methanol-helium system.  An ab
inito interaction potential energy surface was computed at the
Hartree-Fock plus dispersion (HFD) level and employed in the
scattering calculations.  The rotational-internal rotational
behavior of the methanol molecule was described using the
internal axis method (IAM).  The collisional behavior was
described using the infinite-order sudden (IOS) approximation. 
The results show interesting propensity rules which depend on the
ratio of the moments of inertia for the internal rotor and the
top as a whole. 
     Preliminary work has also been done for the case of
asymmetric internal rotors, using asymmetrically deuterated
methanol as the model system.  Asymmetric rotors exhibit
non-equivalent multiple potential minima and partially localized
internal rotational states, transitions among which correspond to
isomerization processes.        

                        Monday , 17 October 1994
                                5:30 pm
                        Room 206, Science & Tech. I
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