Theoretical study of laser cooling of the TlF+ molecular ion

Abstract

The feasibility of the thallium monofluoride TlF⁺ molecular ion towards laser cooling is brought into focus through an electronic structure study. Ab initio calculations are carried out to investigate the four lowest-lying electronic states, X²Σ⁺, (1)²Π, (2)²Σ⁺ and (2)²Π, including the spin–orbit coupling effect by employing the Complete Active Space Self Consistent Field (CASSCF) method at the Multireference Configuration Interaction (MRCI) level of theory while invoking Davidson correction (+Q). Potential energy and permanent dipole moment curves are used to determine the corresponding spectroscopic constants and some other equilibrium parameters. Vibrational parameters of vibrational states and transition dipole moments between possible transitions are computed. The calculated parameters are then used to conduct a theoretical study focusing on the potential possibility of TlF⁺ ionic molecule to be laser cooled on the (2)²Π_1/2(ν′)–X²Σ⁺_1/2(ν′′) transition based on Di Rosa's criteria. With the results obtained being promising, a laser cooling optical cycling scheme is proposed to illustrate the number of pump lasers needed with the corresponding wavelengths that were found to lie within the ranges covered by a specific scientific laser.