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

Abstract

The gas-phase kinetics of phenyl radical ( • C 6 H 5 ) with ethyl formate (HCO 2 Et, EF) was investigated experimentally using ultrasensitive laser-based cavity ring-down spectroscopy (CRDS). Phenyl radicals were generated by photolyzing nitrosobenzene (C 6 H 5 NO) 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 (N 2 ) as diluent. The temperaturedependent Arrhenius expression for the test reaction was obtained as: k Expt,260−361K phenyl+EF =(1.20 ± 0.16) × 10 -13 exp[− (435.6 ± 50.0)/T] cm 3 molecule −1 s −1 and the rate coefficient at room temperature was measured out to be: k Expt,298K phenyl+EF =(4.54 ± 0.42) × 10 -14 cm 3 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: k Theory,200−400K phenyl+EF = (1.48 ± 0.56) × 10 -38 × T 8.47 × exp [(2431.3 ± 322.0)/T] cm 3 molecule −1 s −1 and the corresponding rate coefficient at room temperature was calculated to be: k Theory,298K phenyl+EF = 4.91 × 10 -14 cm 3 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.

Experimental and Theoretical Investigation of Reactions of Formyl (HCO) Radicals in the Gas Phase: (I) Kinetics of HCO Radicals with Ethyl Formate and Ethyl Acetate in Tropospherically Relevant Conditions

“…The home-built PLP-CRDS apparatus was explained in detail in our previous publications. , A schematic diagram of the experimental setup is shown in Figure S1 (Supporting Information, SI). In brief, a linear Fabry–Pérrot optical cavity was established between two highly reflective mirrors ( R = 99.995%) via properly aligning the probe laser beam at a perpendicular angle with respect to the photolysis laser beam.…”

“…17C and Gaussrate-17 program suites (by Truhlar and his co-workers from the University of Minnesota, Minneapolis, MN). the detailed methodology for calculating CVT/SCT rate coefficients was denoted in our previous publications , and is discussed in brief in the Discussion-1 section of the Supporting Information.…”