Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-01-12
J.Phys.Chem. A108 (2004) 25
Astronomy and Astrophysics
Astrophysics
26 pages, 3 figures; w supplement: 8 pages, 8 figures
Scientific paper
Rapid, efficient deactivation of the photoexcited PAH cations accounts for their remarkable photostability and have important implications for astrochemistry, as these cations are the leading candidates for the species responsible for the diffuse interstellar bands (DIB) observed throughout the Galaxy.Ultrafast relaxation dynamics for photoexcited PAH cations isolated in boric acid glass have been studied using femtosecond and picosecond transient grating spectroscopy. With the exception of perylene+, the recovery kinetics for the ground doublet (D0) states of these radical cations are biexponential, containing a fast (< 200 fs) and a slow (3-20 ps) components. No temperature dependence or isotope effect was observed for the fast component, whereas the slow component exhibits both the H/D isotope effect (1.1-1.3) and strong temperature dependence (15 to 300 K). We suggest that the fast component is due to internal Dn to D0 conversion and the slow component is due to vibrational energy transfer (VET) from a hot D0 state to the glass matrix.
Chronister Eric L.
Crowell Robert A.
Lian Rui
Liu An Dong
Pommeret Stanislas
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