Theoretical investigations of the gas phase reaction of limonene (C10H16) with OH radical

The rate coefficients of hydroxyl radical (OH) reaction with limonene were computed using canonical variational transition state theory with small-curvature tunnelling between 275 and 400 K. The geometries and frequencies of all the stationary points are calculated using hybrid density functional theory methods M06-2X and MPWB1K with 6-31+G(d,p), 6-311++G(d,p), and 6-311+G(2df,2p) basis sets. Both addition and abstraction channels of the title reaction were explored. The rate coefficients obtained over the temperature range of 275–400 K were used to derive the Arrhenius expressions: k(T) = 4.06×10^?34 T^7.07 exp4515/T] and k(T) = 7.37×10^?25 T^3.9 exp3169/T] cm³ molecule^?1 s^?1 at M06-2X/6-311+G(2df,2p) and MPWB1K/6-311+G(2df,2p) levels of theory, respectively. Kinetic study indicated that addition reactions are major contributors to the total reaction in the studied temperature range. The atmospheric lifetime (τ) of limonene due to its reactions with various tropospheric oxidants was calculated and concluded that limonene is lost in the atmosphere within a few hours after it is released. The ozone production potential of limonene was computed to be (14–18) ppm, which indicated that degradation of limonene would lead to a significant amount of ozone production in the troposphere.