  Optical methods of enantiomeric-specific state transfer had been proposed
theoretically based on a cyclic three-level system of chiral molecule.
According to these theoretical methods, recently the breakthrough progress has
been reported in experiments [S. Eibenberger et al., Phys. Rev. Lett. 118,
123002 (2017); C. P\'{e}rez et al., Angew. Chem. Int. Ed. 56, 12512 (2017)] for
cold gaseous chiral molecules but with low state-specific enantiomeric
enrichment. One of the limiting factors is the influence of the thermal
population in the selected three purely rotational states in experiment. Here,
we theoretically propose an improved optical method of enantiomeric-specific
state transfer to effectively evade such an adverse impact of thermal
population by introducing ro-vibrational transitions for the cyclic three-level
system of chiral molecules. Then, at the typical temperature in experiments
approximately only the lowest state in the chosen three-level system is
thermally occupied and the optical method of enantiomeric-specific state
transfer works well. Comparing with the case of purely rotational transitions
where all the three states are thermally occupied, this modification will
remarkably increase the obtained state-specific enantiomeric enrichment with
enantiomeric excess approximately 100%.
