A comprehensive gas-phase kinetics of α-methyl thiophene with Cl-atom and OH-radical: Experimental and theoretical studies

Abstract

The rate coefficient for the reaction of methyl thiophene (MeTp) with Cl atom was measured to be (1.09 ± 0.24) × 10⁻¹⁰ cm³ molecule⁻¹s⁻¹ at 298K and 760 Torr using the relative rate (RR) method. The experimental temperature-dependent rate coefficient was measured to be ${k\left(T\right)}^{258-358K}=\left(2.08\pm 0.10\right)\times {10}^{-11}\exp \left[\left(484.5\pm 15.4\right)/T\right]$ cm³ molecule⁻¹ s⁻¹. The theoretical rate coefficients for the reaction of MeTp with Cl-atom and OH radical were calculated at BD(T)/VDZ//BHandHLYP/6–31+g∗ and BD(T)/AVDZ//M06-2X/6–311++g∗∗ level of theory respectively. The Arrhenius equation from the theoretically calculated rate coefficients for MeTp + Cl using the MESMER simulation was obtained to be ${k\left(T\right)}_{\text{MeTp}+\text{Cl}}^{200-400K}=\left(2.44\pm 0.12\right)\times {10}^{-11}\exp \left[\left(438.2\pm 14.9\right)/T\right]$ cm³ molecule⁻¹ s⁻¹. The experimental and theoretical rate coefficients show a negative temperature dependence behaviour over the studied temperature range. The rate coefficient for MeTP + OH was calculated as ${k\left(T\right)}_{200-400K}^{\text{CVT}/\text{SCT}}=\left(2.83\pm 0.20\right)\times {10}^{-13}\exp \left[\left(1641.7\pm 20.6\right)/T\right]$ cm³ molecule⁻¹ s⁻¹ from CVT/SCT methods. Following the MESMER simulation for MeTp + OH reaction, the Arrhenius expression was found to be ${k\left(T\right)}_{\text{MeTp}+\text{OH}}^{200-400K}=\left(8.31\pm 0.53\right)\times {10}^{-12}\exp \left[\left(588.9\pm 19.2\right)/T\right]$ cm³ molecule⁻¹ s⁻¹. At 298 K, the rate coefficient was calculated to be 5.60 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and 6.23 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the reaction of MeTp with OH from CVT/SCT method and MESMER simulations. Both calculation methods demonstrated a negative temperature dependency over the temperature range of 200–400 K. No pressure dependency was observed over the 5–760 Torr in the MESMER calculations. The atmospheric lifespan of MeTp was estimated to be ∼100 days in ambient conditions and ∼1 day in polluted or coastal areas.