“Kinetics of IO Radicals with Ethyl Formate and Ethyl Acetate: A Study using Cavity Ring-Down Spectroscopy and Theoretical Methods”
K. Mondal, A. Kumar & B. Rajakumar. Phys. Chem. Chem. Phys. 2021, 23(45), 25974-25993.

The gas phase kinetics of the reactions of IO radicals with ethyl formate (EF) and ethyl acetate (EA) were investigated experimentally using cavity ring-down spectroscopy (CRDS). IO radicals were generated in situ in the CRD reaction zone by photolyzing a mixture of (CH3I + O3 + N2) at 248 nm and thereby probed at 445.04 nm. The rate coefficients for the reaction of (IO + EF) and (IO + EA) were measured at a total pressure of 65 Torr of N2 in the temperature range of 258-358 and 260-360 K respectively. The rate coefficients for the reaction of (IO + EF) and (IO + EA) were measured experimentally at room temperature to be: k_(IO+EF)^(Expt,298K)=(3.38±0.67)×10-14 and k_(IO+EA)^(Expt,298K)=(1.56±0.30)×10-13 cm3 molecule-1 s-1 respectively. The effects of pressure and photolysis laser fluence on the kinetics of the test reactions were found to be negligible within the experimental uncertainties for the studied range. To complement our experimental findings, kinetics for the title reactions were investigated theoretically using Canonical Variational Transition State Theory (CVT) with Small Curvature Tunnelling (SCT) at CCSD(T)//M06-2X/def2-SV(P) level of theory in the temperatures between 200 and 400 K. A very good agreement was observed between the experimentally measured and theoretically calculated rate coefficients for both the reactions at 298 K. Thermochemical parameters as well as branching ratios for the title reactions are also discussed in the manuscript. Figure: Pseudo-first order plot for the reaction of IO radical with various concentrations of EF, [EF]: C1 = 1.67 × 10^16; C2 = 2.23 × 10^16; C3 = 2.79 × 10^16; C4 = 3.33 × 10^16; C5 = 3.88 × 10^16; C6 = 4.54 × 10^16 molecules cm-3 at 298 K and 65 Torr pressure of N2. The time delays between photolysis and probe laser was varied from 0 to 1 ms with an interval of 100 µs at a laser frequency of 2 Hz. The inset shows the CRDS ring-down decay profile obtained during the course of experiments. Figure: Plot showing the variation of the experimentally measured rate coefficients for the reactions of IO radicals with EF and EA with the experimental total pressures ranging from 39–143 and 40–148 Torr, respectively. Theoretically calculated pressure-dependent rate coefficients calculated via MESMER using RRKM theory are depicted here for better comparison (see details in the ESI†). The solid and dotted lines indicate the linear fits and the uncertainties are in 2σ.