Hamburg 2009 – scientific programme
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MO: Fachverband Molekülphysik
MO 17: Stossprozesse, Energietransfer 2
MO 17.4: Talk
Wednesday, March 4, 2009, 17:15–17:30, VMP 6 HS-G
An analytic model of molecular collisions in fields — •Mikhail Lemeshko and Bretislav Friedrich — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
We present an analytic model of thermal state-to-state rotationally inelastic collisions of molecules in electric, magnetic and radiative fields. The model is based on the Fraunhofer scattering of matter waves and requires Legendre moments characterizing the “shape" of the target in the body-fixed frame as its input. External fields orient or align the target in the space-fixed frame and thereby effect a striking alteration of the dynamical observables: both the phase and amplitude of the oscillations in the partial differential cross sections undergo characteristic field-dependent changes that transgress into the partial integral cross sections. As the cross sections can be evaluated for a field applied parallel or perpendicular to the relative velocity, the model also offers predictions about steric asymmetry. The model has been developed for collisions of (i) closed shell atoms with polar 1 Σ and 2 Π molecules in electrostatic fields; (ii) closed-shell ions with polarizable 1 Σ molecules in laser fields; (iii) closed-shell atoms with paramagnetic 2 Σ, 3 Σ and 2 Π molecules in magnetic fields. We exemplify the field-dependent quantum collision dynamics with the behavior of the Ar-NO(2Π) system in an electrostatic field and He-CaH(2 Σ) system in a magnetic field. A comparison with close-coupling calculations available for the former system [Chem. Phys. Lett. 313, 491 (1999)] demonstrates the model’s ability to qualitatively explain the field dependence of all the scattering features observed.