Exploring the Theoretical Kinetic Analysis of Halogen Monoxide (XO, X = Cl, Br, I) Reactivity with Isoprene across Diverse Temperatures

The rate coefficients for the reactions for XO (XO, X = Cl, Br, I) + isoprene were calculated using the RRKM and ILT approach in master equation simulation (MESMER) in the temperature range of 200-400 K at 1 atm pressure. The thermochemical and energy parameters for ClO + isoprene were calculated using the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31g(2df,p) theory. In the case of the BrO and IO radical reaction, all thermochemical parameters were calculated using CCSD(T)/AVDZ//M06-2X/AVDZ (AVDZ = aug-cc-pVDZ for C, H, and O atoms and aug-cc-pVDZ-pp for the Br atom with effective core potential (ECP) approximation) and CCSD(T)/AVDZ_ecp//M06-2X/AVDZ_ecp (AVDZ_ecp = aug-cc-pVDZ for C, H, and O atoms and Def2SVP for I atom with ECP), respectively. The rate coefficient for the reaction ClO + isoprene was calculated as <i>k</i>(<i>T</i>)_{200-400 K}^ClO+isoprene = (3.63 ± 0.35) × 10^-13 exp - (32.5 ± 30.2)/<i>T</i> cm³ molecule^-1 s^-1 at 1 atm. The rate coefficients for isoprene + BrO and isoprene + IO were calculated in the temperature range of 200-400 K at 1 atm as <i>k</i>(<i>T</i>)_{200-400 K}^BrO+isoprene = (2.33 ± 0.07) × 10^-13 exp(431.8 ± 8.1)/<i>T</i> cm³ molecule^-1 s^-1 and <i>k</i>(<i>T</i>)_200-400K^IO+isoprene = (5.71 ± 0.12) × 10^-13 exp(678.8 ± 6.2)/<i>T</i> cm³ molecule^-1 s^-1. The rate coefficients measured for BrO and IO radicals show a negative temperature dependence over 200-400 K.