To determine the free energy of the system along the reaction coordinate ξ and obtain reliable high-pressure limit rate coefficient, we used an advanced sampling technique known as umbrella sampling. The methodology and theoretical framework are presented in detail in ref. , thus this work only provides a brief overview. This method is based on a stratification strategy that divides the range of the reaction coordinates into windows and applies a bias potential to confine the system to sample within each window. The bias potential typically has the form of a simple harmonic potential: