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dc.creatorMaccarone, Alan T.en_US
dc.creatorHeazlewood, B. R.en_US
dc.creatorRowling, S. J.en_US
dc.creatorKable, S. H.en_US
dc.date.accessioned2008-07-15T13:38:38Z
dc.date.available2008-07-15T13:38:38Z
dc.date.issued2008en_US
dc.identifier2008-FB-12en_US
dc.identifier.urihttp://hdl.handle.net/1811/33363
dc.descriptionP. L. Houston and S. H. Kable, PNASB. R. Heazlewood et al, submittedS.-H. Lee and I.-C. Chen, Chem. Phys.en_US
dc.descriptionAuthor Institution: School of Chemistry, University of Sydney, Sydney NSW 2006, Australiaen_US
dc.description.abstractRecent experiments and theory have implicated a "roaming" mechanism as being important in the photodissociation of $\chem{CH_3CHO}$ into the molecular products $\chem{CH_4}$ + $\chem{CO}$.}, \textbf{103}, 16079 (2006).}$^{,}$} (2006).} As much as 80\% of the flux for this chemical channel was attributed to roaming; the conventional transition state mechanism is a minor contribution. Quasi-classical trajectory calculations reveal that many of these roaming trajectories can be described as a methyl group roaming around the $\chem{HCO}$ core, before intramolecularly abstracting the formyl $\chem{H}$ atom. A crucial element to this mechanism is that the simple, barrierless, C-C bond cleavage to radical products must be open at the wavelengths used in previous experiments. While there is no doubt that the radical channel is open in an energetic sense, $\chem{HCO}$ and $\chem{CH_3}$ have never been observed from the ground state ($\textit{S}$${_0}$) surface. In this seminar, we will summarize the evidence for roaming in $\chem{CH_3CHO}$ and then present new experimental evidence that $\chem{HCO}$ and $\chem{CH_3}$ are indeed formed on the ground state. Pump/probe experiments were performed on acetaldehyde seeded in a supersonic expansion of helium. $\chem{HCO}$ products were probed via laser-induced fluorescence ($\tilde{B}\leftarrow\tilde{X}$) at a range of pump wavelengths (308 - 330 nm). When the pump energy was above the ($\textit{T}$${_1}$) barrier for dissociation ($\lambda$ $\sim$320 nm),}, \textbf{220}, 175 (1997).} the $\chem{HCO}$ product state distribution is characteristic of a reaction proceeding over a barrier. When the dissociation energy is lower than the triplet barrier, $\chem{HCO}$ was still observed, which must then arise from reaction on the $\textit{S}$${_0}$ surface. In addition, the $\chem{HCO}$ internal energy distribution was different when dissociating above and below the triplet barrier, thereby confirming the presence of two different mechanistic pathways. The existence of the $\chem{CH_3}$ + $\chem{HCO}$ channel from the $\chem{CH_3CHO}$ ground state supports the previous assignment of "$\chem{CH_3}$ roaming" in $\chem{CH_3CHO}$ photodissociation to $\chem{CH_4}$ + $\chem{CO}$.en_US
dc.language.isoEnglishen_US
dc.publisherOhio State Universityen_US
dc.titleEVIDENCE FOR DISSOCIATION FROM THE $\textit{S}$${_0}$ GROUND STATE OF ACETALDEHYDE TO THE RADICAL PRODUCTS CH$_3$ and HCOen_US
dc.typeArticleen_US


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