Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier

Journal Article · Sat Aug 14 00:00:00 EDT 2010 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3474993· OSTI ID:21559899

Amaral, G A; Arregui, A; Rodriguez, J D; Banares, L ^[1]

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1. Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid 28040 (Spain)

The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S{sub 1}, which, in turn, undergoes intersystem crossing to the first excited triplet state T{sub 1}. On the triplet surface, the molecule dissociates into CH{sub 3} and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T{sub 1}. However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S{sub 0} after internal conversion from S{sub 1}. We have characterized the fragments' KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T{sub 1} is presented.

• OSTI ID: 21559899
• Journal Information: Journal of Chemical Physics, Vol. 133, Issue 6; Other Information: DOI: 10.1063/1.3474993; (c) 2010 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION
ACETALDEHYDE
DISSOCIATION
EXCITATION
INTERNAL CONVERSION
KINETIC ENERGY
MOLECULES
PHOTOLYSIS
PHOTONS
RADICALS
SURFACES
TRIPLETS
WAVELENGTHS
ALDEHYDES
BOSONS
CHEMICAL REACTIONS
CONVERSION
DECAY
DECOMPOSITION
ELEMENTARY PARTICLES
ENERGY
ENERGY-LEVEL TRANSITIONS
MASSLESS PARTICLES
MULTIPLETS
NUCLEAR DECAY
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
SORPTION