Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study.

Abstract

The relative rate (RR) technique was used for the measurement of OH-initiated photooxidation reactions of ethyl 2-methylpropionate (E2MP) and ethyl 2,2-dimethylpropionate (E22DMP) in the temperature range of 268-363 K at 760 Torr. In addition to this, the thermodynamic and kinetic parameters for the title reactions were theoretically investigated using CCSD(T)/cc-pVTZ//M06-2X/6-311++G(2d,2p) level of theory in the temperature range of 200-400 K using canonical variational transition state theory (CVT) in combination with small curvature tunneling (SCT) method. The rate coefficients at (298 ± 2) K were measured to be kE2MP+OH = (2.71 ± 0.79) × 10-12 cm3 molecule-1 s-1 and kE22DMP+OH = (2.58 ± 0.80) × 10-12 cm3 molecule-1 s-1. The degradation mechanisms for the title reactions were investigated in the presence of O2 using gas chromatography with mass spectrometry (GC-MS) and gas chromatography with infrared spectroscopy (GC-IR). From the recognized products, the possible product degradation mechanisms were predicted. In addition to this, the atmospheric lifetimes (ALs), lifetime-corrected radiative forcing (RF), global warming potential (GWPs) and photochemical ozone creation potentials (POCPs) were calculated to further understand the environmental impact of these molecules on the Earth's troposphere.