In the last few decades, there have been numerous discussions about the destruction of the ozone layer in the mid stratosphere due to chlorine and bromine radicals. However, both in the tropics and mid-latitudes, substantial ozone depletion has been reported which cannot be solely explained based on the local emission of these halogen radicals and it was suggested by Solomon et al. that the chemical reaction induced by iodine atoms are relevant in the stratospheric ozone depletion because of strong convective transports in the tropics and mid-latitudes. Recently, IO radicals have been detected in the Antarctic troposphere with measured averaged concentrations of up to 10 pptv (i.e. ~2.5×108 radicals cm-3) and they undergo heterogeneous uptake to aerosol particles and often lead to particle growth as well as aerosol formation in the MBL. To the best of our knowledge, there is no report in the literatures regarding the kinetics of the reaction of IO radicals with potential biofuels like, ethyl formate (HCO2Et, EF) and ethyl acetate (CH3CO2Et, EA). EF is used in various applications such as an industrial solvent, food flavorings, perfumes, fungicide and larvicide in processed foods etc. EA is an industrial bulk product that is extensively used as a solvent and diluent in paints, coatings, adhesives, inks, organic synthesis and pharmaceutical industries. The kinetics for the reaction of (IO+EF) and (IO+EA) were investigated in the temperature range of 258-358 and 260-360 K respectively at 2 Hz and 65 Torr of pressure with N2 using an in-built pulsed laser photolysis cavity ring-down spectroscopy (CRDS) setup. IO radicals were generated in situ by photolyzing a mixture of (CH3I+O3+N2) at 248 nm and thereby probed at 445.04 nm. The dependency of the rate coefficients with the experimental pressures and the photolysis laser fluences were also verified. Moreover, the kinetics of test reactions were investigated theoretically between the temperatures 200 and 400 K employing Canonical Variational Transition state theory (CVT) along with the Small Curvature Tunneling (SCT) corrections at CCSD(T)//M06-2X/def2-SV(P) level of theory. In addition, the thermodynamic parameters as well as the branching ratios of the individual reaction channels were calculated.

Investigation of gas phase kinetics of IO radical with potential biofuels using cavity ring-down spectroscopy and theoretical methodologies

ACS Fall 2021

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