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EP/J015865/1 - Roaming dynamics in photochemistry

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Dr C Murray EP/J015865/1 - Roaming dynamics in photochemistry

Principal Investigator - School of Chemistry, University of Glasgow

Scheme

First Grant Scheme

Research Areas

Chemical Reaction Dynamics and Mechanisms Chemical Reaction Dynamics and Mechanisms

Start Date

04/2012

End Date

03/2014

Value

£113,606

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Grant Description

Summary and Description of the grant

Chemical processes that are initiated by the absorption of light are of tremendous fundamental and practical importance. Much of the chemical processing that occurs in planetary atmospheres is carried out by reactive species produced by sunlight while laboratory chemical syntheses can be by driven by the use of various light sources. An understanding of fundamental photochemistry is crucial for modelling natural processes and optimizing industrial uses. Indeed, deep understanding is essential if optical excitation is to be used to control the outcomes of chemical reactions.
Photodissociation dynamics research examining partitioning of the excess energy among the internal degrees of freedom of the products has provided a sensitive probe of the electronically excited potential energy surfaces (PESs) and provided deep insight into the nature of chemical bonding. The concept of the PES, which relies on the Born-Oppenheimer approximation that the electronic and nuclear motions are separable, is fundamental to our understanding of chemical reactivity. The topology of the PES provides the forces that act upon the atoms as chemical processes occur and controls the energy disposal in the products. An important region of the PES is the transition state, a specific arrangement of the atoms that separates reactants from products. The geometry and characteristics of the transition state is used in transition state theories to calculate the rates of chemical processes.
Key challenges in chemical dynamics exist where these long-standing pillars of reaction theory fall. In particular the role of nonadiabatic processes that occur over multiple PEss and the role of non-traditional mechanisms that bypass conventional transition states are of tremendous importance in contemporary research. A novel photochemical mechanism has recently been identified that has profound implications for long-standing concepts in chemical reactivity and methods used to calculate the rates of reactions. In this so-called "roaming" mechanism, open-shell radical photoproducts make extended excursions in the attractive long-range region of the PES before ultimately reacting to give closed-shell products. The long-range abstraction reaction avoids the conventional well-defined tight transition state on the ground state PES and results in markedly different product quantum state distributions.
This project will extend recent fundamental photodissociation dynamics research by seeking evidence of roaming dynamics in the photochemistry of small organic molecules. State-of-the-art velocity map imaging methods, exploiting both state-selective and universal ionization techniques will measure the correlated partitioning of the excess energy among the photoproducts, identifying and characterizing the branching into roaming pathways. A novel roaming mechanism that further involves crossing between adiabatic PESs and the formation of reactive triplet radical species will be investigated in detail. The existence of the roaming mechanism has profound implications for chemical reaction theory and the use of transition state theory to calculate reaction rates. A deeper understanding of this mechanism, and crucially its generality, will impact upon modelling of photochemistry in planetary atmospheres, in combustion diagnostics and industrial applications.

Structured Data / Microdata


Grant Event Details:
Name: Roaming dynamics in photochemistry - EP/J015865/1
Start Date: 2012-04-01T00:00:00+00:00
End Date: 2014-03-31T00:00:00+00:00

Organization: University of Glasgow

Description: Chemical processes that are initiated by the absorption of light are of tremendous fundamental and practical importance. Much of the chemical processing that occurs in planetary atmospheres is carried out by reactive species produced by sunlight while lab ...