Evans, Nicholas L., Yu, Hui, Roberts, Gareth M., Stavros, Vasilios G. and Ullrich, Susanne (2012) Observation of ultrafast NH3 (Ã) state relaxation dynamics using a combination of time-resolved photoelectron spectroscopy and photoproduct detection. Physical Chemistry Chemical Physics, Volume 14 (Number 30). pp. 10401-10409. doi:10.1039/c2cp40178a ISSN 1463-9076.

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Abstract

The ultrafast excited state relaxation of ammonia is investigated by resonantly exciting specific vibrational modes of the electronically excited NH3 (Ã) state using three complementary femtosecond (fs) pump–probe techniques: time-resolved photoelectron, ion-yield and photofragment translational spectroscopy. Ammonia can be seen as a prototypical system for studying non-adiabatic dynamics and therefore offers a benchmark species for demonstrating the advantages of combining the aforementioned techniques to probe excited state dynamics, whilst simultaneously illuminating new aspects of ammonia's photochemistry. Time-resolved photoelectron spectroscopy (TRPES) provides direct spectroscopic evidence of σ* mediated relaxation of the NH3 (Ã) state which manifests itself as coupling of the umbrella (ν2) and symmetric N–H stretch (ν1) modes in the photoelectron spectra. Time-resolved ion yield (TRIY) and time-resolved photofragment translation spectroscopy (TRPTS) grant a measure of the dissociation dynamics through analysis of the H and NH2 photodissociation co-fragments. Initial vibrational level dependent TRIY measurements reveal photoproduct formation times of between 190 and 230 fs. Measurement of H-atom photoproduct kinetic energies enables investigation into the competition between adiabatic and non-adiabatic dissociation channels at the NH3 (Ã)/NH3 () conical intersection and has shown that upon non-adiabatic dissociation into NH2 () + H, the NH2 () fragment is predominantly generated with significant fractions of internal vibrational energy.

Item Type:	Journal Article
Divisions:	Faculty of Science, Engineering and Medicine > Science > Chemistry
Journal or Publication Title:	Physical Chemistry Chemical Physics
Publisher:	Royal Society of Chemistry
ISSN:	1463-9076
Official Date:	14 August 2012
Dates:	Date Event 14 August 2012 Published
Volume:	Volume 14
Number:	Number 30
Page Range:	pp. 10401-10409
DOI:	10.1039/c2cp40178a
Status:	Peer Reviewed
Publication Status:	Published

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