<p><a></a><a>Toluene’s removal mechanism in the atmosphere is mainly attributed to OH radical, which
includes major OH-addition and minor H-abstraction reactions. The cresols and RO2 derived from OHadducts reacting to O2 have significant impacts on the generation of secondary organic aerosols (SOA) and
O3. However, computed branching ratios of various OH-adducts at various theoretical levels are largely
inconsistent, mainly because previously reported barrier heights of OH-addition reaction showed a strong
method dependence. In the present study, we demonstrate that this reaction involves a nonnegligible
anharmonic effect (during the process of OH moving to the benzene ring), which has been overlooked by
previous studies. The reaction kinetics of toluene + OH was systematically studied by a high-level quantum
chemical method (CCSD(T)-F12/cc-pVQZ-F12//B2PLYP-D3/6-311++G(d,p)) combined with
RRKM/master equation simulations. The particle-in-a-box approximation was used to treat the
anharmonicity in this system. The final total rate coefficient is calculated to be 2.60 × 10−12 cm3 molecule−1
s−1 at 300 K and 1 atm. The main products for toluene + OH are computed as ortho-adducts (50.8%), benzyl
radical + H2O (21.1%), ipso-adduct (16.3%), para-adduct (6.1%), and meta-adduct (4.6%). Our results
indicate that both high level quantum chemical calculations for the crucial barrier heights and appropriate
treatments for the anharmonicity determine the accuracy of the final computed total rate coefficients and
branching ratios. Further analysis on the branching ratios of various reaction channels provides insight into
the atmosphere-initiated oxidation of toluene. </a></p>