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Physical Review A

Radiative association processes to specific rovibrational levels in low-energy Na++Rb87 collisions

Lisong Yan, Xingyu Li, Yong Wu, J. G. Wang, Y. Z. Qu

Published Sep 18, 2014• 4 citations
Publisher

Abstract

The radiative association processes for ${\mathrm{Na}}^{+}$ colliding with $^{87}\mathrm{Rb}(5s)$ atoms have been investigated by using the quantum-mechanical method. The total and partial cross sections that associate to the specific rovibrational states are calculated rigorously in the energy range of ${10}^{\ensuremath{-}13}\ensuremath{-}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The association cross sections display rich resonance structures. The ratios of rotationally resolved cross sections to total association cross sections and the ratios of vibrationally resolved cross sections to rotationally resolved cross sections are calculated and presented. For energies less than ${10}^{\ensuremath{-}9}\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, association to $X\phantom{\rule{0.16em}{0ex}}{}^{2}{\ensuremath{\Sigma}}^{+}$ ($J=1$) dominates over all other association states. As the energy increases, each resonance of the total cross sections is associated with the given angular component of specific bound states. In the energy range of ${10}^{\ensuremath{-}13}\ensuremath{-}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, the vibrational states $v\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}27$ and $v\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}28$ are the most probable final states. The probability for the formation of molecular ion ${\mathrm{NaRb}}^{+}$ in the rovibrational states is discussed. The existence of Cooper minima in the radiative association cross sections is found and illustrated.

DOI
10.1103/physreva.90.032714

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Full-dimensional quantum scattering calculations are reported for ro-vibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H2_22​-H2_22​ system. Several near-resonant ro-vibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low energy resonant features in the energy dependence of the cross sections are identified. The computed results are in agreement with total cross sections reported in previous experimental results, including resonant features in the energy dependence of the cross section. In particular, low-energy cross sections show a strong resonant feature associated with an l=3l=3l=3 partial wave in the incident channel. Rate coefficients for several inelastic rotational and ro-vibrational transitions are reported for temperatures ranging from 0.10.10.1 K to 200200200 K and they display a maximum between 111 K-101010 K reflecting the important contributions from the l=3l=3l=3 shape resonance that occurs around 2.5 K.
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Radiative emission during cold collisions between trapped laser-cooled Rb atoms and alkaline-earth ions (Ca+^++, Sr+^++, Ba+^++) and Yb+^++, and between Li and Yb+^++, are studied theoretically, using accurate effective-core-potential based quantum chemistry calculations of potential energy curves and transition dipole moments of the related molecular ions. Radiative association of molecular ions is predicted to occur for all systems with a cross section two to ten times larger than the radiative charge transfer one. Partial and total rate constants are also calculated and compared to available experiments. Narrow shape resonances are expected, which could be detectable at low temperature with an experimental resolution at the limit of the present standards. Vibrational distributions are also calculated, showing that the final molecular ions are not created in their ground state level.
Nonadiabatic inelastic collision cross sections have been computed at low and ultralow energies, focusing in the present work on the Ca+{}^{+}+(4s2S)(4s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}S)(4s2S) + Rb(5s2S)(5s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}S)(5s2S) $\ensuremath{\rightarrow}$ Ca(4s4p3P)(4s4p{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}P)(4s4p3P) + Rb+(1S){}^{+}{(}^{1}\phantom{\rule{-0.16em}{0ex}}S)+(1S) charge-exchange process at ultralow collision energies (EEE $\ensuremath{\leqslant}$ 10${}^{\ensuremath{-}6}$ eV) induced by spin-orbit nonadiabatic coupling terms. The calculations reveal a wealth of sharp resonances which can substantially enhance charge-exchange probabilities over a specific energy window of around 10${}^{\ensuremath{-}6}$ to 10${}^{\ensuremath{-}8}$ eV. Such resonances are analyzed in detail, and the corresponding molecular mechanism is discussed for a specific example, where the nonadiabatic transition probabilities are seen to increase by nearly 2 orders of magnitude.
The close coupling calculation of rotationally inelastic collision of He with Na2 is first performed by employing a recently computed ab initio potential energy surface. The process of rovibrational energy excitation and relaxation of Na2 in collision with He has been studied in detail based on the single and double exitations coupled cluster with a noniterative perturbation treatment of triple excitations CCSD （T） potential energy surface. Our results are in good agreement with the experimental results. Our results show that: （1）The elastic cross section（Δj=0） is much larger than the inelastic cross section. （2）The largest amplitude occurs at small scattering angles. At low Δj transition, the He projectile is predominantly forward scattering. Backward scattering occurs as Δj increases. （3）For inelastic cross section, the most effective transition is that with Δj=2.（4）The fast narrow diffraction oscillations in the cross sections are the obvious characteristics for the low Δj inelastic transitions, which decreases with increasing j. （5）The elastic differential-cross-sections（DCS）provides a useful visualization of rotational rainbows at low translational energy. It is beneficial to reducing the loss in molecular cooling and trapping.