Nonrigidity effects -- a missing puzzle piece in the description of low-energy anisotropic molecular collisions

Abstract

Cold collisions serve as a very sensitive probe of the interaction potential. In the recent study of Klein et al. (Nature Phys. 13, 35-38 (2017)) the one-parameter scaling of the interaction potential was necessary to obtain agreement between theoretical and observed patterns of the orbiting resonances for excited metastable helium atoms colliding with hydrogen molecules. Here we show that the effect of nonrigidity of the H2 molecule on the resonant structure, absent in the previous study, is critical to predict correct positions of the resonances in that case. We have complemented the theoretical description of the interaction potential and revised reaction rate coefficients by proper inclusion of the flexibility of the molecule. The calculated reaction rate coefficients are in remarkable agreement with the experimental data without empirical adjustment of the interaction potential. We have shown that even state-of-the-art calculations of the interaction energy cannot ensure agreement with the experiment if such an important physical effect as flexibility of the interacting molecule is neglected. Our findings about the significance of the nonrigidity effects can be especially crucial in cold chemistry, where the quantum nature of molecules is pronounced.

Molecular Collisions: from Near-cold to Ultra-cold

“…It is shown the presence of the single electron in the excited p-orbital of the He atom changes the entire system and resulting spatial polarization brings in a pronounced anisotropic effect in the interaction potential. Mariusz Pawlak et al have studied the effect of nonrigidity of the H 2 molecule on the profile of the scattering resonance using AVT [94], and show the calculated reaction rate coefficients are in excellent agreement with the experimental data after proper inclusion of the flexibility of the molecule into the interaction potential, eliminating the need of empirical adjustment of the interaction potential to match the calculation with the experiment. This finding demonstrates the importance of the flexibility of the interacting molecule, which may be crucial in cold chemistry.…”