We study the isotopic dependence of collisional widths and shifts of the Hg clock transition \(^1\)S\(_0\)–\(^3\)P\(_0\) perturbed by the Rb atoms in the temperature range from 1 nK to 1 K. For this purpose, we model the Born-Oppenheimer effective interaction potential by including the leading long-range van der Waals coefficients. For elastic collisions, we show the connection between line shape parameters in the \({\upmu }\)K temperature range and scattering lengths in ground and excited states as a function of reduced mass of the colliding Hg and Rb atoms. We confront the full quantum scattering calculations with a semi-classical approximation for collisional widths and shifts. We show that the shape resonances in excited and ground scattering states lead to significant variations of collisional line shape parameters with the change of the reduced mass of colliding atoms. We also indicate the possible influence of inelastic collisions, which could lead to universal behavior and significantly affect the dependence of collisional broadening and shifting on the isotopic combination of colliding atoms.
