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Timescales for adiabatic photodissociation dynamics from the à state of ammonia
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Chatterley, Adam S., Roberts, Gareth M. and Stavros, Vasilios G. (2013) Timescales for adiabatic photodissociation dynamics from the à state of ammonia. The Journal of Chemical Physics, Volume 139 (Number 3). 034318. doi:10.1063/1.4811672 ISSN 0021-9606.
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Official URL: http://dx.doi.org/10.1063/1.4811672
Abstract
Photodissociation dynamics after excitation of the A˜ state ν′2 = 4 (umbrella) level of ammonia are investigated using ultrafast time-resolved velocity map ion imaging (TR-VMI). These studies extend upon previous TR-VMI measurements[K. L. Wells, G. Perriam, and V. G. Stavros, J. Chem. Phys.130, 074308 (Year: 2009)]10.1063/1.3072763, which reported the appearance timescales for ground state NH2(X˜)+H photoproducts, born from non-adiabatic passage through an X˜/A˜ state conical intersection (CI) at elongated H–NH2 bond distances. In particular, the present work sheds new light on the formation timescales for electronically excited NH2(A˜)+H species, generated from NH3 parent molecules that avoid the CI and dissociate adiabatically. The results reveal a step-wise dynamical picture for the production of NH2(A˜)+H products, where nascent dissociative flux can become temporarily trapped/impeded around the upper cone of the CI on the A˜ state potential energy surface (PES), while on course towards the adiabatic dissociation asymptote – this behavior contrasts the concerted mechanism previously observed for non-adiabatic dissociation into H-atoms associated with ro-vibrationally “cold” NH2(X˜) . Initially, non-planar NH3 molecules (species which have the capacity to yield adiabatic photoproducts) are found to evolve out of the vertical Franck-Condon excitation region and towards the CI region of the A˜ state PES with a time-constant of 113 ± 46 fs. Subsequently, transient population encircling the CI then progresses to finally form NH2(A˜)+H photoproducts from the CI region of the A˜ state PES with a slower time-constant of 415 ± 25 fs. Non-adiabatic dissociation into ro-vibrationally “hot” NH2(X˜) radicals together with H-atoms is also evidenced to occur via a qualitatively similar process.
Item Type: | Journal Article | ||||
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Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||
Journal or Publication Title: | The Journal of Chemical Physics | ||||
Publisher: | American Institute of Physics | ||||
ISSN: | 0021-9606 | ||||
Official Date: | 2013 | ||||
Dates: |
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Volume: | Volume 139 | ||||
Number: | Number 3 | ||||
Page Range: | 034318 | ||||
DOI: | 10.1063/1.4811672 | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published |
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