Abstract
Close-coupling calculations of the resonance and near resonance charge exchange in ion-atom collisions of Be at low and intermediate energies are presented. Accurate ab initio calculations are carried out of the Born-Oppenheimer potentials and the non-adiabatic couplings that are due to the finite nuclear masses and drive the near resonance charge exchange. We show that the near resonance charge exchange cross section follows Wigner's threshold law of inelastic processes for energies below 10(-8) eV and that the zero temperature rate constant for it is 4.5 × 10(-10) cm(3) s(-1). At collision energies much larger than the isotope shift of the ionization potentials of the atoms, we show that the near resonance charge exchange process is equivalent to the resonance charge exchange with cross sections having a logarithmic dependence. We also investigate the perturbation to the charge exchange process due to the non-adiabatic interaction to an electronic excited state. We show that the influence is negligible at low temperatures and still small at intermediate energies despite the presence of resonances.
Highlights
In the case of near resonance charge exchange (NRCE), the scattering energy is measured from the second channel of 9Be + 10Be+, whose asymptotic energy was set at 5.767 Â 10À5 eV above the lowest limit of 9Be+ + 10Be
We have investigated slow collisions of a Be atom with a Be ion including the case of different isotopes
The computed energy splitting of DE = 56.47 meV in the isotopic combination of the (9Be10Be)+ molecular ion is consistent with the result of 57.76 meV derived from high precision atomic calculations and resonance ionization mass spectroscopy
Summary
The possibility of creating small ensembles of ultracold atoms and molecules has opened new research in physics and chemistry.[1,2,3] The recent experimental production of ultracold molecular ions[4,5,6,7] provides new opportunity for exploring ion–atom interactions[8,9] and collisional dynamics.[10,11,12,13,14,15] Of particular interest of cold molecular ions are novel applications to mass spectrometry, chemistry, and spectroscopy;[16] the implementation of scalable quantum-computation architecture;[17,18,19] the precision measurement tests of fundamental physics;[20] a better understanding of polaron physics;[21] the charge transport at low temperature[22] and producing ion– atom bound states to study many-body physics.[23]. In the case of identical atoms, but with different isotopic composition, we have shown[11,12] that the charge transfer reaction becomes inelastic (near resonant process) This inelastic process is driven by the small non-adiabatic couplings between the two electronic states that are due to the small kinematic effects because of the finite nuclear mass. We believe that the work we present here goes well beyond a mere extension of our previous calculations to another mass combination and adds an interesting new element to the picture that may help in understanding the effects of this small non-adiabatic perturbation to collision processes governed by a strong polarization potential and to the prototypical two-state description of the charge exchange
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