Photodissociation Dynamics of Acetaldehyde

Benjamin Shepler, Joel Bowman and Bastiaan Braams, Department of Chemistry, Emory University

 Recently, two mechanisms have been described for the photodissociation of formaldehyde to form molecular products H₂ + CO.  The dominant pathway involves a conventional transition state (TS) saddle point that separates reactants from products.  The minor pathway involves an intramolecular hydrogen abstraction and has been dubbed a “roaming” mechanism.  Acetaldehyde has been proposed as a second molecule that may exhibit a so-called roaming mechanism that bypasses the conventional TS.  To simulate the photodissociation of acetaldehyde several independent full-dimensional potential energy surfaces  (PES) have been constructed based on data sets of 130, 000 and 230, 000 ab initio data points.  Details of the construction of the PES and comparison to accurate benchmarks will be presented.  Quasiclassical trajectory calculations have been run on these PES to simulate the 308 nm photodissociation of acetaldehyde.  Trajectories were initiated at both the acetaldehyde equilibrium geometry and the conventional transition state dividing acetaldehyde from the molecular products CH₄ + CO.  The results of these trajectory calculations will be compared with recent experimental reports of the CO rotational distribution and CH₄ vibrational distribution produced from the photodissociation of acetaldehyde.

Oral