科研之友
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摘要
A theoretical investigation on the suitability of laser cooling AlF+ and AlCl+ molecular ions is performed by employing ab initio calculations. Four low-lying electronic states are determined using the multi-reference configuration interaction method plus Davidson correction. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. The Franck-Condon factors (FCFs) and radiative lifetimes are verified by calculating the potential energy curves (PECs) and transition dipole moments for the C (2)Pi (v') -> X (2) Sigma(+) (v), C (2)Pi (v') -> A (2) Pi (v) and C (2)Pi (v') -> B (2)Sigma(+) (v) transitions. Our calculation indicates that the C (2)Pi (v') -> X (2) Sigma(+) (v) transition is provided with sufficiently diagonally distributed FCFs and the radiative lifetimes for the C (2)Pi (v') vibrational state are short enough for rapid laser cooling for both AlF+ and AlCl+ molecular ions. However, our calculation also indicates that the AlF+ radical is not suitable for laser cooling due to the predissociation of the C (2)Pi state. The calculation and analysis of the electronic states demonstrate the possibility of AlCl+ for laser cooling, and give more insight into the behavior of these four low-lying electronic states for further experimental and theoretical study. Its laser-cooling scheme requires one main pumping laser (lambda(00) = 268 nm) and three repumping lasers (lambda(10) = 272 nm lambda(21) = 273 nm and lambda(31). =. 278 nm). Moreover, the low mass, short radiative lifetime and small vibrational branching loss ratios to the intervening states make the AlCl+ radical suitable for laser cooling in theory.
