Full-dimensional quantum mechanical study of three-body recombination for cold 4He-4He-20Ne system.

The increase of the number of the two-body recombination channels strongly challenges the numerical calculation of the accurate rates for the three-body recombination (TBR) process and its reverse process, collision-induced dissociation (CID), at ultracold temperatures. By taking the 4He-4He-20Ne collision system as an example, we have obtained the rates for its TBR and CID processes involving all four recombination channels, including the two-body states 4He2 (l = 0) and 4He20Ne (l = 0, 1, 2) with l the rotational quantum number. By using the adiabatic hyperspherical method, we have considered not only total angular momentum J = 0 but also J > 0 in the ultracold collision energies (E = 0.01 - 100 mK × kB). It is found that 4He2 (l = 0) is the major product after the TBR process in the ultracold limit (E ≤ 0.1 mK × kB). The TBR rate into 4He2 (l = 0) is nearly one order of magnitude larger than the sum of the other three products, 4He20Ne (l = 0, 1, 2). Moreover, the CID rates for the three 4He20Ne (l = 0, 1, 2) + 4He initial states are close to each other and are smaller than that for the 4He2 (l = 0) + 20Ne initial state. Additionally, we have, for the first time, performed the channel-resolved scattering calculation that can explain the above-mentioned findings quantitatively.

Fock-space relativistic coupled cluster study on the RaF molecule promising for the laser cooling.

The potential energy curves of the ground and five low-lying excited terms of the RaF molecule are calculated using the Fock-space relativistic coupled theory. The electronic term energies, equilibrium internuclear distances, transition and permanent dipole moments, sequences of vibrational energies, harmonic vibrational frequencies, Franck-Condon factors, and radiative lifetimes are predicted. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. The scheme for the direct laser cooling involving the first excited A2П1/2 state is proposed. The data obtained in this study suggests the A2П1/2 â†’ X2Σ+ channel in the RaF molecule is the almost ideal case for direct laser cooling. It is quite possible that the effective cooling scheme for the RaF molecule can be realized using only one pump laser.