Quasiclassical simulations based on cluster models reveal vibration-facilitated roaming in the isomerization of CO adsorbed on NaCl.

The desire to better understand the quantum nature of isomerization led to recent experimental observations of the vibrationally induced isomerization of OC–NaCl(100) to CO–NaCl(100). To investigate the mechanism of this isomerization, we performed dynamics calculations using finite (CO–NaCl)n cluster models. We constructed new potential energy surfaces for CO–NaCl and CO–CO interactions using high-level ab initio data and report key properties of the bare CO–NaCl potential energy surface, which show much in common with the experiment. We investigated the isomerization dynamics using several cluster models and, in all cases, isomerization was seen for highly excited CO vibrational states, in agreement with experiments. A detailed examination of the reaction trajectories indicates that isomerization occurs when the distance between CO and NaCl is larger than the distance at the conventional isomerization saddle point, which is a strong indicator of ‘roaming’. Recent experiments reporting the isomerization of CO on a NaCl(100) surface—from C adsorbed to O adsorbed—represent a major challenge to simulate from first principles. Now, using dynamics calculations and (CO–NaCl)n cluster models that feature CO–CO interactions, it is found that isomerization occurs via a ‘roaming’ mechanism at a large distance from the NaCl(100) surface.