Quantum and structural effects captured via a statistical method: The SACM applied to HCN and HNC colliding with CO

This study spotlights the statistical adiabatic channel model as an efficient and accurate method for deriving low-temperature (de)-excitation rate coefficients for collisions induced by heavy projectiles. For such systems, fully quantum treatments become intractable, while quasi-classical methods fail at low temperature. Here, we demonstrate that the statistical adiabatic channel model overcomes these limitations by combining statistical sampling with an adiabatic channel representation. Its application to the HCN and HNC isomers colliding with CO yields rate coefficients in quantitative agreement with full quantum results benchmarked for the lowest total angular momentum. These systems are relevant for modeling cometary comae, where reliable molecular data remain scarce. Remarkably, this approach also reproduces near-resonant energy transfer and isomeric effects, demonstrating that essential quantum and structural features can be captured within a statistical framework.