ИСТИНА

Recent advances in trapping and cooling molecular species have opened up new opportunities for studying barrierless reactions at low and ultralow temperatures (see, e.g., ref. [1]). Reaction of this type are still challenging for rigorous quantum scattering theory, whereas the underlying global or long-range potential energy surfaces (PESs) are amenable for accurate ab initio calculations. Capture approximation in its classical (Langevin) sense [2] is applicable at high temperatures and can be combined with the ab initio PESs by means of adiabatic channel models [3]. For ultracold regime, analytical versions of the quantum capture approximation have been developed within the quantum defect theory for analytical inverse-power R-n potentials that model the lowest-order long-range intermolecular interaction [4]. In order to bridge the gaps between two extremes and between model analytical and numerical adiabatic channel potentials fully numerical method for quantum capture probability calculation is proposed [6]. It combines the Truhlar-Kupperman [5] method for tunneling through potential barrier with the capture boundary conditions of zero reflection at dividing surface stabilized with respect to the surface position. Two applications of the method are discussed. The reaction rates between polarized and unpolarized KRb molecules calculated using the ab initio long-range PES [7] below 10 K are compared with experimental results [1] and quantum defect models. The rates of the Li + CaH [8] reaction are computed with the ab initio PES [9] for the temperature range from 1 nK to 10 K in order to trace out the validity of classical and quasiclassical WKB approximations, as well as the approximation of the global PES by its the lowest-order long-range interaction component. This research was supported by the RFBR grants Nos. 11-03-00081 and 14-03-00422. 1. S. Ospelkaus, K.-K. Ni, D. Wang, M.H.G. de Miranda, B. Neyenhuis, G. Quéméner, P.S. Julienne, J.L. Bohn, D.S. Jin, and J. Ye, Science 327, 853 (2010). 2. P. Langevin, Ann. Chem. Phys. 5, 245 (1905). 3. J. Troe, J. Chem. Phys. 87, 2773 (1987); D.C. Clary, Annu. Rev. Phys. Chem. 41, 61 (1990). 4. Z. Idziaszek, G. Quéméner, J.L. Bohn, and P.S. Julienne, Phys. Rev. A. 82, 020703 (2010); B. Gao, Phys. Rev. Lett. 105, 263203 (2010). 5. D.G. Truhlar and A. Kuppermann, J. Am. Chem. Soc. 93, 1840 (1971). 6. A.A. Buchachenko, Moscow Univ. Chem. Bull. 53, 159 (2012). 7. A.A. Buchachenko, A.V. Stolyarov, M.M. Szczęśniak, and G. Chałasiński, J. Chem. Phys. 137, 114305 (2012). 8. V. Singh, K.S. Hardman, N. Tariq, M.-J. Lu, A. Ellis, M.J. Morrison, and J.D. Weinstein, Phys. Rev. Lett. 108, 203201 (2012). 9. T.V. Tscherbul, J. Kłos, and A.A. Buchachenko, Phys. Rev. A 84, 040701(R) (2011).