Photochemistry of Simple Aldehydes and Ketones in the Gas Phase

Lee, Edward K. C.; Lewis, Roger S.

doi:10.1002/9780470133422.ch1

Cited by 33 publications

(3 citation statements)

References 233 publications

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“…Aliphatic aldehydes exhibit a weak absorption band in the wavelength range 240−360 nm as a result of a dipole forbidden n → π* transition. 5,6 Photolysis of aldehydes can possibly occur through the following pathways:…”

Section: Introductionmentioning

confidence: 99%

“…Aliphatic aldehydes exhibit a weak absorption band in the wavelength range 240–360 nm as a result of a dipole forbidden n → π* transition. , Photolysis of aldehydes can possibly occur through the following pathways: RCHO + h ν → RH + CO → normalR + HCO → normalR ′ + CH 3 CHO → RCO + normalH Process 1 is the molecular fragmentation channel. Process 2 represents the fragmentation into free radicals (Norrish type I reaction).…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Triplet-State Photochemistry of Pentanal: Mechanisms of Norrish I, Norrish II, and H Abstraction Reactions

2013

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The photochemistry of aldehydes in the gas phase has been the topic of extensive studies over the years. However, for all but the smallest aldehydes the dynamics of the processes is largely unknown, and key issues of the mechanisms are open. In this article, the photochemistry of pentanal is studied by dynamics simulation using a semiempirical MRCI code for the singlet and triplet potential energy surfaces involved. The simulations explore the processes on the triplet state following intersystem crossing from the initially excited singlet. Test simulations show that the photochemistry takes place on the adiabatic triplet surface only and that no nonadiabatic transitions occur to the other triplets. The main findings include the following: (1) Norrish type I and type II reactions and H detachment have been observed. (2) The time scales of Norrish type I and Norrish type II reactions are determined: Norrish type I reaction tends to occur in the time scale below 10 ps, whereas the Norrish type II reaction is mostly pronounced after 20 ps. The factors affecting the time scales are analyzed. (3) The relative yield for Norrish type I and type II reactions is 34% and 66%, which is close to the experimental observed ones. Bond orders and Mulliken partial charges are computed along the trajectories and provide mechanistic insights. The results throw light on the time scales and mechanisms and competition between different channels in aldehyde photochemistry. It is suggested that direct dynamics simulations using semiempirical potentials can be a very useful tool for exploring the photochemistry of large aldehydes, ketones, and related species.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics of Triplet-State Photochemistry of Pentanal: Mechanisms of Norrish I, Norrish II, and H Abstraction Reactions

2013

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“…One of the main issues is to understand how the multiple bond-breaking steps are temporally correlated and how the available energy is distributed among the fragments. The photodissociation of simple aliphatic ketones at sufficiently high energy is one example in which the two α-CC bonds can break to produce three fragments: two alky radicals and a carbon monoxide molecule. , This so-called Norrish type I α-cleavage reaction is one of the most important photochemical reactions. − Being the simplest aliphatic ketone, the photodissociation of acetone in the ultraviolet region has attracted much attention for decades, partly because it is regarded as a prototype for the Norrish type I reaction − and partly because of its important roles in atmospheric photochemistry. , At sufficiently high energies, it is energetically possible to break the two equivalent α-CC bonds, and therefore, the “concertedness” of the two-bond breakage had been an issue of concern. − Through femtosecond (fs) time-resolved experiments, it has been shown unambiguously that the eliminations of the two methyl groups take place via a stepwise mechanism regardless of the excitation energy. − However, detailed dissociation pathways at such high energies in acetone have not been fully elucidated, and controversies still remained in the literature. − …”

Section: Introductionmentioning

confidence: 99%

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Chen

Cheng

2005

J. Phys. Chem. A

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The photodissociation dynamics of the acetone S2 (n, 3s) Rydberg state excited at 195 nm has been studied by using femtosecond pump-probe mass-selected multiphoton ionization spectroscopy. For the first time, the temporal evolutions of the initial state, intermediates, and methyl products were simultaneously measured and analyzed for this reaction to elucidate the complex dynamics. Two mechanisms were considered: (1) the commonly accepted mechanism in which the primary dissociation occurs on the first triplet-state surface, and (2) the recently proposed mechanism in which the primary dissociation takes place on the first singlet-excited-state surface. Our results and analyses supported the validity of the new mechanism. On the other hand, the conventional mechanism was found to be inadequate to describe the observed dynamics. The temporal evolution of methyl products arising from the secondary dissociation of hot acetyl intermediates exhibited a very complex behavior that can be ascribed to the combination of a nonuniform initial vibrational distribution and the competition between dissociation and slow intramolecular vibrational redistribution.

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Dynamics of Photochemical Reactions of Organic Carbonyls and their Clusters

Shemesh

Gerber

2016

Advances in Chemical Physics Volume 159

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Photochemistry of Simple Aldehydes and Ketones in the Gas Phase

Cited by 33 publications

References 233 publications

Dynamics of Triplet-State Photochemistry of Pentanal: Mechanisms of Norrish I, Norrish II, and H Abstraction Reactions

Dynamics of Triplet-State Photochemistry of Pentanal: Mechanisms of Norrish I, Norrish II, and H Abstraction Reactions

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Dynamics of Photochemical Reactions of Organic Carbonyls and their Clusters

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