Brute force in molecular reaction dynamics: A novel technique for measuring steric effects

摘要

We present the theoretical foundation of a novel technique for the orientation of sum;hyphen;molecules and symmetric tops with permanent electric dipole moment. The method bases on the adiabatic transformation of free rotational states into those of librational oscillations taking place during the passage of a molecule into a strong electric field. Several examples of calculated spatial distributions of the molecular axis are given. The computational results demonstrate that in connection with highly relaxed supersonic nozzle beams only moderately strong electric fields are required to generate a marked orientation of the axis. In a first application of this technique we studied steric effects of the reaction K+CH3Irarr;KI+CH3at two elevated collision energies (0.79 and 1.24 eV). All observed steric effects could be rationalized in terms of a simple impulsive reaction model. We find that backward scattered products are more likely formed if the approaching atoms face the Ihyphen;end of CH3Imdash;in agreement with low energy resultsmdash;while forward scattered products are favorably formed if the CH3hyphen;end is encountered.