Accurate determination of blackbody radiation shifts in a strontium molecular lattice clock

Molecular lattice clocks enable the search for new physics, such as fifth forces or temporal variations of fundamental constants, in a manner complementary to atomic clocks. Blackbody radiation (BBR) is a major contributor to the systematic error budget of conventional atomic clocks and is notoriously difficult to characterize and control. Here, we combine infrared Stark-shift spectroscopy in a molecular lattice clock and modern quantum chemistry methods to characterize the polarizabilities of the Sr₂ molecule from dc to infrared. Using this description, we determine the static and dynamic blackbody radiation shifts for all possible vibrational clock transitions to the 10⁻¹⁶ level. This constitutes an important step toward millihertz-level molecular spectroscopy in Sr₂ and provides a framework for evaluating BBR shifts in other homonuclear molecules.