Theoretical study of isomerization and decomposition of propenal

We investigated the dynamics of isomerization and multi-channel dissociation of propenal (CH2CHCHO), methyl ketene (CH3CHCO), hydroxyl propadiene (CH2CH2CHOH), and hydroxyl cyclopropene (cyclic-C3H3-OH) in the ground potential-energy surface using quantum-chemical calculations. Optimized structures and vibrational frequencies of molecular species were computed with method B3LYP/6-311G(d,p). Total energies of molecules at optimized structures were computed at the CCSD(T)/6-311+G(3df,2p) level of theory. We established the potential-energy surface for decomposition to CH2CHCO + H, CH2CH + HCO, CH2CH2/CH3CH + CO, CHCH/CH2C + H2CO, CHCCHO/CH2CCO + H-2, CHCH + CO + H-2, CH3 + HCCO, CH2CCH + OH, and CH2CC/cyclic-C3H2 + H2O. Microcanonical rate coefficients of various reactions of trans-propenal with internal energies 148 and 182 kcal mol(-1) were calculated using Rice-Ramsperger-Kassel-Marcus and Variational transition state theories. Product branching ratios were derivable using numerical integration of kinetic master equations and the steady-state approximation. The concerted three-body dissociation of trans-propenal to fragments C2H2 + CO + H-2 is the prevailing channel in present calculations. In contrast, C3H3O + H, C2H3 + HCO and C2H4 + CO were identified as major channels in the photolysis of trans-propenal. The discrepancy between calculations and experiments in product branching ratios indicates that the three major photodissociation channels occur mainly on an excited potential-energy surface whereas the other channels occur mainly on the ground potential-energy surface. This work provides profound insight in the mechanisms of isomerization and multichannel dissociation of the system C3H4O. (C) 2011 American Institute of Physics. [doi:10.1063/1.3521274]