Investigation of kinetics of phenyl radicals with ethyl formate in the gas phase using cavity ring-down spectroscopy and theoretical methodologies

The gas-phase kinetics of phenyl radical (·C6H5) with ethyl formate (HCO2Et, EF) was investigated experimentally using ultrasensitive laser-based cavity ring-down spectroscopy (CRDS). Phenyl radicals were generated by photolyzing nitrosobenzene (C6H5NO) at 248 nm and thereby probed at 504.8 nm. The rate coefficients for the (phenyl radical + EF) reaction were investigated between the temperatures of 260 and 361 K and at a pressure of 61 Torr with nitrogen (N2) as diluent. The temperature-dependent Arrhenius expression for the test reaction was obtained as: kphenyl+EFExpt,260-361K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{k}}_{\mathrm{phenyl}+\mathrm{EF}}^{\mathrm{Expt}, 260-361\mathrm{K}}$$\end{document}=(1.20  ±  0.16) × 10–13 exp[−(435.6  ±  50.0)/T] cm3 molecule−1 s−1 and the rate coefficient at room temperature was measured out to be: kphenyl+EFExpt,298K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{k}}_{\mathrm{phenyl}+\mathrm{EF}}^{\mathrm{Expt},298\mathrm{K}}$$\end{document}=(4.54  ±  0.42) × 10–14 cm3 molecule−1 s−1. The effects of pressure and laser fluence on the kinetics of the test reaction were found to be negligible within the experimental uncertainties. To complement the experimental findings, kinetics for the reaction of phenyl radicals with EF was investigated theoretically using Canonical Variational Transition State Theory (CVT) with Small Curvature Tunnelling (SCT) at CCSD(T)/cc-pVDZ//B3LYP/6–31 + G(d,p) level of theory in the temperatures between 200 and 400 K. The theoretically calculated rate coefficients for the title reaction were expressed in the Arrhenius form as: kphenyl+EFTheory,200-400K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{k}}_{\mathrm{phenyl}+\mathrm{EF}}^{\mathrm{Theory},200-400\mathrm{K}}$$\end{document}= (1.48  ±  0.56) × 10–38 × T8.47 × exp[(2431.3  ±  322.0)/T] cm3 molecule−1 s−1 and the corresponding rate coefficient at room temperature was calculated to be: kphenyl+EFTheory,298K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{k}}_{\mathrm{phenyl}+\mathrm{EF}}^{\mathrm{Theory},298\mathrm{K}}$$\end{document}= 4.91 × 10–14 cm3 molecule−1 s−1. A very good agreement was observed between the experimentally measured and theoretically calculated rate coefficients at 298 K. Thermochemical parameters as well as branching ratios for the reaction of (phenyl radical + EF) are also discussed in this manuscript.