Mid-infrared spectra of pyrolyzed 1- and 2-iodopropane

A. Del Valle, L. Lazarus, O. Sandoval, and S.L. Nickolaisen

Department of Chemistry and Biochemistry, California State University, Los Angeles

Ozone is the most harmful oxidant in urban smog. Although it is naturally occurring in small amounts, it is known to have many adverse health effects at higher concentrations. Professor Scott Nickolaisen's group at CSULA is involved in experimental studies of alkyl and alkyl peroxy radicals to determine their contribution to ozone formation. The group is also using a variety of computational techniques to help with their understanding of the chemistry of these radicals.

Electronic structure calculations are employed to obtain the potential energy surfaces for possible dissociation pathways of relevant species. The figure below shows such surfaces for the n-propyl and i-propyl radicals. Density functional theory calculations for the latter suggest that it only dissociates through one channel, while n-propyl can dissociate via two different paths, of which, the one leading to the C₂H₄ and CH₃ products is more favorable.

Molecular dynamics (MD) simulations indicate that n-propyl radicals at the transition state predominantly undergo dissociation to products. Initial results conclude that 100% of the trajectories at 900K are dissociative, but this ratio is reduced considerably at lower temperatures. However, more calculations must be performed to obtain ensemble averages for comparison of trajectories for dissociative processes versus relaxation back to the equilibrium radical geometry. The figure below shows results of MD calculations performed using density functional theory (B3LYP) with the 6-31(D) basis set, starting at transition state TS3.