Radiative charge transfer in collisions of H+ with Na at very low energies

The radiative charge transfer for H++Na(3s) collisions has been investigated by using both the optical-potential and semiclassical methods in the energy ranges of 10(-6)-10 and 10(-2)-100 eV, respectively, which are in agreement in the overlapping energy region. The relevant molecular potentials and dipole matrix elements were obtained from the multireference single- and double-excitation configuration interaction approach. The radiative charge-transfer cross sections display rich resonance structures, due to the formation of quasibound rotational-vibrational molecular states, in the energy range below 0.2 eV. The present radiative charge-transfer cross-section results disagree with the calculations of Watanabe [Phys. Rev. A 66, 044701 (2002)]. The rate coefficient is obtained for temperatures between 0.1 and 20 000 K. Below 7000 K, it has a nearly constant value of approximately 1.7x10(-13) cm(3) s(-1), which is about 1/3 of that of Watanabe The nonradiative charge transfer becomes dominant at energies above 4 eV.