Mondal Koushik, Rajakumar Balla
Department of Chemistry, Indian Institute of Technology Madras, Chennai, 600036, India.
Centre for Atmospheric and Climate Sciences, Indian Institute of Technology Madras, Chennai, 600036, India.
Environ Sci Pollut Res Int. 2023 Feb;30(9):22590-22605. doi: 10.1007/s11356-022-23494-8. Epub 2022 Oct 27.
Kinetics of the reaction of IO radicals with methanol (MeOH) and ethanol (EtOH) were experimentally studied in the gas phase using pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS). IO radicals were produced in situ at the reaction zone by photolysing a mixture of precursors (CHI + O + N) at 248 nm and thereby electronically excited at 445.04 nm. The rate coefficients for the reactions of (IO + MeOH) and (IO + EtOH) were measured at a total pressure of 60 Torr/N in the range of 258-360 K. At room temperature, the experimental rate coefficients of the title reactions were measured to be [Formula: see text] and [Formula: see text]. Dependencies of the kinetics with photolysis laser fluence and experimental pressures were verified. Effects of pressure over the kinetic behaviour of the studied systems were observed to be insignificant within the statistical uncertainties when studied in the range of ~ 30-150 Torr/N, whereas a minor and linear fluence dependency was observed within the studied limit. From the measured kinetic parameters, the atmospheric lifetimes of MeOH and EtOH were calculated in the tropospherically relevant conditions regarding their reactions with important atmospheric oxidants like Cl atom, OH and IO radicals. To complement experimental results, kinetics and thermochemistry for the title reactions were investigated theoretically via canonical variational transition state (CVT) theory in combination with small curvature tunnelling (SCT) corrections with a dual-level Interpolated Single Point Energy (ISPE) approach at the CCSD(T)/def2-QZVPP//M06-2X/def2-TZVPP level of theory/basis set in the temperatures between 200 and 400 K. Good degree of agreement was encountered between experimentally measured and theoretically calculated rate coefficients. This article also discusses the thermochemical parameters and kinetic branching ratios (BRs) of all the pathways involved in the title reactions.
采用脉冲激光光解-腔衰荡光谱法（PLP-CRDS）在气相中对碘氧自由基（IO）与甲醇（MeOH）和乙醇（EtOH）反应的动力学进行了实验研究。通过在248 nm波长下光解前驱体混合物（CHI + O + N）在反应区原位产生IO自由基，并使其在445.04 nm处发生电子激发。在60 Torr/N的总压力下，于258 - 360 K范围内测量了（IO + MeOH）和（IO + EtOH）反应的速率系数。在室温下，测得标题反应的实验速率系数分别为[公式：见原文]和[公式：见原文]。验证了动力学与光解激光能量密度和实验压力的相关性。当在约30 - 150 Torr/N范围内研究时，观察到压力对所研究体系动力学行为的影响在统计不确定度范围内不显著，而在所研究的极限范围内观察到了较小的线性能量密度依赖性。根据测得的动力学参数，计算了甲醇和乙醇在对流层相关条件下与重要大气氧化剂如氯原子、羟基自由基和碘氧自由基反应的大气寿命。为补充实验结果，在CCSD(T)/def2-QZVPP//M06-2X/def2-TZVPP理论水平/基组下，采用规范变分过渡态（CVT）理论结合小曲率隧道效应（SCT）校正和双水平内插单点能量（ISPE）方法，在200至400 K的温度范围内对标题反应的动力学和热化学进行了理论研究。实验测量的速率系数与理论计算值之间具有良好的一致性。本文还讨论了标题反应中所有途径的热化学参数和动力学分支比（BRs）。
