  Acetaldehyde (AA) isomerization (to vinylalcohol, VA) and decomposition (into
either CO+CH$_4$ and H$_2$+H$_2$CCO) is studied using a fully dimensional,
reactive potential energy surface represented as a neural network (NN). The NN,
trained on 432'399 reference structures from MP2/aug-cc-pVTZ calculations has a
MAE of 0.0453 kcal/mol and an RMSE of 1.186 kcal/mol for a test set of 27'399
structures. For the isomerization process AA $\rightarrow$ VA the minimum
dynamical path implies that the C-H vibration, and the C-C-H (with H being the
transferring H-atom) and the C-C-O angles are involved to surmount the 68.2
kcal/mol barrier. Using an excess energy of 93.6 kcal/mol - the energy
available in the solar spectrum and sufficient to excite to the first
electronically excited state - to initialize the molecular dynamics, no
isomerization to VA is observed on the 500 ns time scale. Only with excess
energies of $\sim$ 127.6 kcal/mol (including the zero point energy of the AA
molecule), isomerization occurs on the nanosecond time scale. Given that
collisional de-excitation at atmospheric conditions in the stratosphere occurs
on the 100 ns time scale, it is concluded that formation of VA following
photoexcitation of AA from actinic photons is unlikely. This also limits the
relevance of this reaction pathway to be a source for formic acid.
