Exact quantum scattering calculations of transport properties: CH2(X̃3B1, ã1A1)-helium.

Transport properties for collisions of methylene, in both its ground X̃(3)B1 and low-lying ã(1)A1 electronic states, with helium have been computed using recently computed high-quality ab initio potential energy surfaces (PESs). Because of the difference in the orbital occupancy of the two electronic states, the anisotropies of the PESs are quite different. The CH2(ã)-He PES is very anisotropic because of the strong interaction of the electrons on the helium atom with the unoccupied CH2 orbital perpendicular to the molecular plane, while the anisotropy of the CH2(X̃)-He PES is significantly less since this orbital is singly occupied in this case. To investigate the importance of the anisotropy on the transport properties, calculations were performed with the full potential and with the spherical average of the potential for both electronic states. Significant differences (over 20% for the ã state at the highest temperatures considered) in the computed transport properties were found.