On the intramolecular vibrational energy redistribution dynamics of aromatic complexes: A comparative study on C₆H₆–C₆H₅Cl, C₆H₆–C₆H₃Cl₃, C₆H₆–C₆Cl₆ and C₆H₆–C₆H₅F, C₆H₆–C₆H₃F₃, C₆H₆–C₆F₆

This article focuses on the unimolecular dissociation dynamics of benzene-based aromatic complexes, specifically examining how the coupling between intramolecular and intermolecular vibrational modes influences their dissociation rates. Through chemical dynamics simulations of six complexes—benzene–monofluorobenzene (Bz–MFB), benzene–monochlorobenzene (Bz–MCB), benzene–trifluorobenzene (Bz–TFB), benzene–trichlorobenzene (Bz–TCB), benzene–hexafluorobenzene (Bz–HFB), and benzene–hexachlorobenzene (Bz–HCB)—the study finds that neither very weak nor very strong vibrational coupling favors fast dissociation; instead, an intermediate coupling optimizes the dissociation rate, with Bz–TFB exhibiting the fastest dissociation. Manipulating vibrational frequencies by altering atomic masses, such as reducing chlorine mass in Bz–HCB to mimic Bz–TFB frequencies, increases dissociation rates, highlighting the role of vibrational frequency gaps in energy flow and dissociation dynamics. Power spectrum analyses confirm that stronger coupling leads to greater energy backflow from intermolecular to intramolecular modes, slowing dissociation, and the study also proposes corrections to the Arrhenius equation to account for restricted intramolecular vibrational energy redistribution (IVR) and anharmonicity effects. These findings contribute to understanding non-RRKM behavior in weakly bound aromatic complexes and suggest broader implications for similar van der Waals systems.