Blackbody thermalization and vibrational lifetimes of trapped polyatomic molecules

We study the internal state dynamics of optically trapped polyatomic molecules subject to room-temperature blackbody radiation. Using rate equations that account for radiative decay and blackbody excitation between rovibrational levels of the electronic ground state, we model the microscopic behavior of the molecules' thermalization with their environment. As an application of the model, we describe in detail the procedure used to determine the blackbody and radiative lifetimes of low-lying vibrational states in ultracold CaOH molecules, the values of which were reported in previous work [C. Hallas et al., Phys. Rev. Lett. 130, 153202 (2023)]. Ab initio calculations are performed and are found to agree with the measured values. Vibrational-state lifetimes for several other laser-coolable molecules, including SrOH and YbOH, are also calculated.