Accurate ab initio potential energy surfaces are essential to understand and predict collisional outcomes in ultracold molecular systems. In this study, we explore the intermolecular interactions between two laser-cooled CaF molecules, in both their ground and excited electronic states, aiming to understand the mechanisms behind the observed collisional losses on the nonreactive, spin-polarized surface of the $\mathrm{CaF}+\mathrm{CaF}$ system. Using state-of-the-art ab initio methods, we compute 12 electronic states of the ${\mathrm{Ca}}_2{\mathrm{F}}_2$ complex within the rigid rotor approximation applied to CaF. Calculating the potential energy surfaces for the excited electronic states of ${\mathrm{Ca}}_2{\mathrm{F}}_2$ is challenging and computationally expensive. Our approach employs the multireference configuration interaction method, restricted to single and double excitations, along with a reasonably large active space to ensure the convergence in the excited states. We also compute the spin-orbit coupling between the ground state and the lowest spin-polarized triplet state, as well as the spin-spin coupling within the lowest triplet state (1) ${}^3{\mathrm{A}}^{\prime }$. Additionally, we determine the electric transition dipole moments for the (1) ${}^3{\mathrm{A}}^{\prime }$–(2) ${}^3{\mathrm{A}}^{\prime }$ and (1) ${}^3{\mathrm{A}}^{\prime }$–(1) ${}^3{\mathrm{A}}^{″}$ transitions. Notably, we find that the lowest spin-polarized state (1) ${}^3{\mathrm{A}}^{\prime }$, shifted by 1064 nm of laser light from the optical dipole trap, intersects several electronically excited states. Finally, by analyzing the potential energy surfaces, we discuss two plausible pathways that may account for the observed collisional losses on the spin-polarized surface of the $\mathrm{CaF}+\mathrm{CaF}$ system.

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• Chemical Physics & Physical Chemistry
• Cold and ultracold molecules