Speaker
Prof.
Paul Mayer
(University of Ottawa)
Description
Polycyclic aromatic hydrocarbon (PAH) molecules have been postulated to be key species in astrochemistry. This proposal has motivated numerous laboratory studies to advance our understanding of the formation and evolution of these species in space and their impact on the physics and chemistry of interstellar and circumstellar environments. In particular, PAHs absorb UV photons from stars, which can lead to their photoionization and dissociation and therefore limit their survival in astrophysical environments. Molecular H2 is the most prolific molecular species found in the interstellar medium (ISM). Whereas it has been long recognized that H2 is formed on dust grains, investigation of the involved mechanisms is still a very active subject of research. One popular theory is that polycyclic aromatic hydrocarbons (PAH) may play a role in the formation of H2 by acting as catalysts. Atomic hydrogen would adsorb onto the surface of the molecules, thus hydrogenating the PAHs, prior to the desorption of H2. This reaction channel demonstrates the importance of investigating the energetics of not only PAHs but modified PAHs as well, such as hydrogenated species.
In this presentation, we have explored the photoionization and subsequent unimolecular dissociation of small PAH molecules ranging from naphthalene, anthracene and pyrene as well as two dihydrogenated species 1,2-dihydronaphthalene and 9,10-dihydrophenanthrene using the imaging photoelectron photoion coincidence apparatus at the Swiss Light Source. RRKM modeling of the competitive dissociation pathways provides reliable reactions energetics and entropics that agree with reactions mechanisms derived from calculations and tandem mass spectrometry.
Not only does the derived data from the above experiments allow speculation on the stability and chemical role of PAHs in the interstellar environment, they have also been used as standard systems to probe the reliability of modeling the dissociation of these systems by collision-induced dissociation mass spectrometry. A brief summary of these results will also be presented in this presentation.
Primary author
Prof.
Paul Mayer
(University of Ottawa)
Co-authors
András Bödi
(Paul Scherrer Institut)
Prof.
Balint Sztaray
(University of the Pacific)
Ms
Brandi West
(University of Ottawa)
Prof.
Christine Joblin
(L’Institut de Recherche en Astrophysique et Planétologie, CESR)
Patrick Hemberger
(Paul Scherrer Institut)
Prof.
Valerie Blanchet
(CELIA -Bordeaux)
