Acetaldehyde Photodissociation

Y. Kurosaki. Hydrogen-atom production channels of acetaldehyde photodissociation direct DFT molecular dynamics study, J. Mol. Struct. - THEOCHEM 850 9—16 (2008). 

G. A. Amaral, A. Arregui, L. Rubio-Lago, J. D. Rodriguez, and L. Banares. Imaging die radical channel in acetaldehyde photodissociation competing mechanisms at energies close to die triplet... 

Reactions with molecular species above the arrow e.g. RIO) involve subsequent reactions with these species to produce the indicated products. In most cases the reactants shown to the left of the arrow participate in the slowest or rate-determining step]. The CH3O radical formed in Rll then follows reaction R7. The H02 radical formed in RIO is the other member of the family and is linked with HO in a variety of chain reactions. These radicals are produced following HO attack on hydrocarbons or by photodissociation of oxygenated hydrocarbons such as formaldehyde (RIO) and acetaldehyde ... 

Reactions without wells can also exhibit multiple pathways due to deviation from the MEP. While many trajectories may follow the MEP over a saddle point, alternative pathways arise when forces on the PES steer away from the saddle point, typically into relatively flat regions of the PES, before finding an additional path to the same exit channel. The roaming mechanisms recently elucidated in the photodissociation of formaldehyde and acetaldehyde, and the reaction of CH3 + O, are examples of this phenomenon, and are discussed in Section V. 

Acetaldehyde is methyl-substituted formaldehyde, and has a number of similarities with its smaller cousin. In particular, when photodissociated at 308 nm, internal conversion to is rapid, and acetaldehyde can decompose via analogous radical and molecular channels... 

To illustrate the application of Eqs. (OO) and (PP), let us calculate the rate of photolysis of acetaldehyde. Aldehydes such as CH3CHO play an important role in tropospheric chemistry because they photodissociate to produce free radicals. In the case of acetaldehyde, there are four possible sets of products ... 

The photochemical decomposition of methanal in a solid Xe matrix has been studied. Work has also been reported dealing with the photodissociation dynamics of methanal, and ab initio calculations have been carried out on the photochemical decomposition of acetaldehyde into methane and CO. The photocatalytic decomposition of acetaldehyde to yield carbon dioxide has also been reported. The threshold for CC bond fission in propanal and the release of the CHO fragment has been shown to be at a wavelength of 326.26 nm. Chowdhury has reported the dissociation of propynal using multiphoton irradiation. Gas-phase photolysis of butyraldehyde in the 280-330 nm range has shown that the CHO radical is produced. ... 

Fig. 2-20. Photodissociation coefficients for N02, HCHO, CHjCHO, and 0( D) produced from ozone, for ground-level, clear-sky conditions. Nitrogen dioxide diamonds are measurements of Madronich et al. (1983), solid points are data of Marx et al. (1984), the solid line represents calculations of Madronich et al. (1983) using the method of Isaksen et al. (1977), and the dashed line is for isotropic scattering. Formaldehyde open points are measurements of Marx el al. (1984), and the solid line represents calculations of Calvert (1980). Acetaldehyde triangles are measurements of Marx et al. (1984), and the solid line represents calculations of Meyrahn et al. (1982). Ozone solid points are measurements of Dickerson et al. (1979) and Bahe et al. (1980) normalized to 325 Dobson units of total ozone overhead, and the solid line represents calculations of Dickerson et al. (1979).

Aliphatic Carbonyl Compounds.—The photodissociation of formaldehyde, acetone, acetaldehyde, and propionaldehyde was studied by Solomon, Jonah, Chandra, and Bersohn, using the photolysis mapping technique. " For each molecule, broadband excitation in the (/> -> n ) band led to an anisotropic distribution of the... 

Kurosaki, Y., and K. Yokoyama (2002), Photodissociation of acetaldehyde, CH3CHO —> CH4 4- CO Direct ah initio dynamics study, J. Phys. Chem., 106, 11415-11421. 

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