C6 coefficients for interacting Rydberg atoms and alkali-metal dimers

We study the van der Waals interaction between Rydberg alkali-metal atoms with fine structure (n²L_j ; L ≤2 ) and heteronuclear alkali-metal dimers in the ground rovibrational state (X ⁺¹Σ ; v =0 , J =0 ). We compute the associated C₆ dispersion coefficients of atom-molecule pairs involving ¹³³Cs and ⁸⁵Rb atoms interacting with KRb, LiCs, LiRb, and RbCs molecules. The obtained dispersion coefficients can be accurately fitted to a state-dependent polynomial O (n⁷) over the range of principal quantum numbers 40 ≤n ≤150 . For all atom-molecule pairs considered, Rydberg states n ^S2_j and n ^P2_j result in attractive 1 /R⁶ potentials. In contrast, n ^D2_j states can give rise to repulsive potentials for specific atom-molecule pairs. The interaction energy at the LeRoy distance approximately scales as n^-5 for n >40 . For intermediate values of n ≲40 , both repulsive and attractive interaction energies of the order of 10-1000 μ K can be achieved with specific atomic and molecular species. The accuracy of the reported C₆ coefficients is limited by the quality of the atomic quantum defects, with relative errors Δ C₆/C₆ estimated to be no greater than 1% on average.