Abstract This study presents a thorough kinetic mechanism of the OH-initiated reaction of fulvenallene (C7H6), a crucial intermediate in the formation of polycyclic aromatic hydrocarbons (PAHs), over a wide T and P range (T = 200 – 2000 K and P = 0.76 – 76,000 Torr), using different computational tools. The temperature- and pressure-dependent behaviors of the title system were investigated through the utilization of the Master Equation rate model, based on the potential energy surface explored at the CCSD(T)/cc-pVQZ//M06–2X/aug-cc-pVTZ level. The model demonstrates that the addition of OH onto C4 of the 1,3-cyclopentadiene fragment of fulvenallene to create adduct 5‑hydroxy-4-vinylidenecyclopent-2-en-1-yl (IM4) is more prevalent at low T (e.g., T ≤...