Theoretical study of isomerization and decomposition of propenal

Abstract

We investigated the dynamics of isomerization and multi-channel dissociation of propenal (CH2CHCHO), methyl ketene (CH 3CHCO), 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 B3LYP6-311G(d,p). Total energies of molecules at optimized structures were computed at the CCSD(T)6-311G(3df,2p) level of theory. We established the potential-energy surface for decomposition to CH2CHCO H, CH 2CH HCO, CH2CH2CH3CH CO, CHCHCH 2C H2CO, CHCCHOCH2CCO H2, CHCH CO H2, CH3 HCCO, CH2CCH OH, and CH 2CCcyclic-C3H2 H2O. Microcanonical rate coefficients of various reactions of trans-propenal with internal energies 148 and 182kcalmol-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 H2 is the prevailing channel in present calculations. In contrast, C3H 3O 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 C 3H4O. © 2011 American Institute of Physics.