Rigorous quantum calculations for atom-molecule chemical reactions in electric fields: From single to multiple...

We present an efficient method for rigorous quantum calculations of cross sections for atom-molecule reactive scattering in the presence of a DC electric field. The wavefunction of the reaction complex is expanded in an overcomplete set of arrangement-dependent Fock-Delves hyperspherical basis functions, and the interactions of the reactants and products with electric fields are accounted for in the total angular momentum representation. A significant computational challenge affecting our previously developed approach [T. V. Tscherbul and R. V. Krems, Phys. Rev. Lett. 115, 023201 (2015)] is addressed by an efficient asymptotic frame transformation between the hyperspherical and Jacobi coordinates in the presence of an external field. Using accurate ab initio potential energy surfaces, we calculate total and state-resolved cross sections for the chemical reactions LiF(v = 1, j = 0) + H → Li + HF(v' = 0, j') and F + HD(v = 0, j = 0) → HF + D, DF + H as functions of collision energy and electric field strength. The field dependence of the cross sections for the LiF + H chemical reaction exhibits resonance structure mediated by tunneling-driven interactions between reactants and products. No significant field effects are found for the F + HD → HF + D, DF + H chemical reaction at 1 K, even for state-resolved transitions and with field magnitudes reaching 200 kV/cm. Our calculations illustrate the essential role of basis set convergence for the proper interpretation of external field effects on chemical reaction dynamics. While reduced-basis calculations for the F + HD reaction indicate significant effects of electric fields on product state distributions, these effects vanish when the number of total angular momentum basis states is increased.