MOLECULAR UNIVERSE

Quantum scattering methods as well as simpler capture models will be applied to calculations of rate constants for reactions controlled by long-range potentials between reagents (e.g. between ions and molecules and between pairs of radicals). Use will also be made of ab initio potentials, especially where chemical bonding contributes to the potential in the crucial, transition state, region (UOXF.DN). Göttingen and UGOT will use a complementary approach—the statistical adiabatic channel model (SACM)—to calculate the same quantities for reactions occurring over attractive potential energy surfaces. These theoretical approaches are complementary to the experimental approaches to reaction kinetics. Collisional rate coefficients can be obtained through theoretical studies, involving both the derivation of the potential energy surface via quantum chemistry and the dynamical treatment of the collisions. Besides standard ab-initio codes (ALCHEMY, MOLPRO, GAUSSIAN), new techniques will be developed, in particular for the determination of bending and inversion motions (Unibas, Bordeaux, U.J.F., Madrid, Meudon, UR1, UOXF.DN, and Warsaw). These potential surfaces will be used in dynamical calculations of rotational and rovibrational excitation of molecules through collisions with H, He, and H₂, using either full close-coupling calculations or less time-consuming treatments with some degrees of freedom frozen. Semi-classical techniques will be used when the relative energy between the perturber and the target is much larger than the energy transfer resulting from the collision. Experimental studies will be specifically carried out to validate the theoretical calculations (KUN). These experiments involve a heavy experimental set-up specific to each collisional system.