Hyperfine structure of the A¹ state of AlCl and its relevance to laser cooling and trapping

The majority of molecules proposed for laser cooling and trapping experiments have Sigma-type ground states. Specifically, (2)Sigma states have cycling transitions analogous to D-1 lines in alkali-metal atoms while (1)Sigma states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with (2)Sigma-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed (1)Sigma-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl-a (1)Sigma molecule-and report on the characterization of the A(1) Pi state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a 3(1) Pi state and photoionization process via the 3(1) Sigma(+) state as possible loss mechanisms for a magneto-optical trap of AlCl.