Electronic states and spin-forbidden cooling transitions of AlH and AlF

Abstract

The feasibility of laser cooling AlH and AlF is investigated using ab initio quantum chemistry. All the electronic states corresponding to the ground and lowest two excited states of the Al atom are calculated using multi-reference configuration interaction (MRCI) and the large AV6Z basis set for AlH. The smaller AVQZ basis set is used to calculate the valence electronic states of AlF. Theoretical Franck-Condon factors are determined for the A(1)Π→ X(1)Σ(+) transitions in both radicals and found to agree with the highly diagonal factors found experimentally, suggesting computational chemistry is an effective method for screening suitable laser cooling candidates. AlH does not appear to have a transition quite as diagonal as that in SrF (which has been laser cooled) but the A(1)Π→ X(1)Σ(+) transition transition of AlF is a strong candidate for cooling with just a single laser, though the cooling frequency is deep in the UV. Furthermore, the a(3)Π→ X(1)Σ(+) transitions are also strongly diagonal and in AlF is a practical method for obtaining very low final temperatures around 3 μK.

Inelastic aluminium-hydrogen collision data for non-LTE applications in stellar atmospheres

“…The calculated ground-state potential agrees perfectly with the accurate ab initio calculations performed by Wells & Lane (2011) for the short-range internuclear distances (R < 12 au). Since the semi-emperical formula (Olson et al 1971) underestimates off-diagonal matrix elements at short distances, the two lowest model potentials are replaced by the ab initio potentials (Wells & Lane 2011), which have the avoided crossing at R = 7.8 au.…”

“…Since the semi-emperical formula (Olson et al 1971) underestimates off-diagonal matrix elements at short distances, the two lowest model potentials are replaced by the ab initio potentials (Wells & Lane 2011), which have the avoided crossing at R = 7.8 au. To the best of our knowledge, no ab initio calculations for higher lying AlH( 1 Σ + ) potentials have been performed 2 , although transitions between higher lying states, including the ionic one, are of the primary interest for astrophysical applications.…”

Theoretical study of laser cooling of magnesium monofluoride usingab initiomethods

“…Until recently, the laser cooling of molecules to ultracold temperatures was verified from the perspective of experiment [9][10][11]. Transverse laser cooling was applied to beams of SrF [9] and YO [10] molecules, and longitudinal laser cooling was applied to a supersonic beam of CaF molecules [11], From a theoretical point of view, a series of diatomic polar molecules were considered to be potential molecules for laser cooling, such as the alkaline-earth-metal monofluorides (e.g., BeF [12] and RaF [13]), the alkalineearth-metal monohydrides [14] (e.g., BeH, MgH, CaH, SrH, and BaH) and other polar molecules (e.g., CH [15] and A1F [16], etc.). According to previous research work [8], the molecule must meet the following criteria to be a promising laser-cooling candidate.…”

Model approach for low-energy inelastic atomic collisions and application to Al+H and Al++H−

“…The atomic data are taken from [46]. The short-range parameters, A ion = 9 a.u., γ ion = 1.7 a.u., A cov = 7 a.u., γ cov = 2.0 a.u., τ = 2.1 a.u., are determined by adjusting the ground adiabatic PEC to the accurate ab initio AlH(X 1 + ) data [47]. The calculated 10 lowest adiabatic PECs, which have the asymptotic limits below or equal to the ionic limit, are shown in Fig.…”

“…show PECs for the states which are below the ionic limit, but their avoided crossings with the ionic PECs take place at distances larger than R = 100 a.u. The symbols are the accurate ab initio data [47]. …”