Theoretical Study On The Laser Cooling Of TlCl And BiH Molecule

Cold and ultracold molecules play important roles in many fields such as precise spectroscopic measurements,ultracold chemistry reaction,and quantum computation and thus have become attractive tools for testing fundamental physics.In this work,using the multi-reference configuration interaction method（MRCI）,we have investigated a potential optical cycling scheme for laser cooling of thallium chloride and bismuth hydride.The main contents are as following:1.The electronic structure and transition properties including potential energy curves transition dipole moment and Franck-Condon factor（FCFs）of thallium chloride（TlCl）and bismuth hydride molecules（BiH）has been investigated based on high-level ab initio calculations with the consideration of the core-valence and the spin-orbit coupling（SOC）effects.2.The possibility of laser cooling of thallium chloride TlCl molecules has been investigated.We show that the a³（47）₀₊-X¹（50）₀₊transition of TlCl is a possible candidate for laser cooling,which features highly diagonal FCFs and no intermediate interacting electronic states.Based on our calculations,we propose an optical cycling scheme by utilizing four lasers at wavelengths around 320 nm with more than 10⁴ cycles for photon absorption/emission and a sub-microkelvin temperature limit.2.The possibility of laser cooling of BiH molecules has been investigated based on high-level ab initio calculations.Based on our calculations,we show that the transition between states b0⁺-X₁0⁺of BiH is a possible candidate for laser cooling,with consideration of the intermediate state X₂1.An optical cycling scheme is proposed by utilizing four lasers at wavelengths around 498 and 626 nm with 5400 cycles for photon absorption/emission and a sub-microkelvin temperature.Our study should shed some light on searching for possible molecular candidates for laser cooling with the existence of an intermediate electronic state.3.In this work,we also study the ion-atom collision in low energy region between the B⁺and H by the quantum-mechanical molecular-orbital close-coupling method（QMOCC）,computing the crossing section of charge transform process.