Issue |
A&A
Volume 432, Number 2, March III 2005
|
|
---|---|---|
Page(s) | 585 - 594 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20042246 | |
Published online | 02 March 2005 |
Theoretical electron affinities of PAHs and electronic absorption spectra of their mono-anions
1
INAF - Osservatorio Astronomico di Cagliari - Astrochemistry Group, Strada n. 54, Loc. Poggio dei Pini, 09012 Capoterra (CA), Italy e-mail: [gmalloci;gmulas;iporcedd]@ca.astro.it
2
Dipartimento di Fisica, Università degli Studi di Cagliari, Complesso Universitario di Monserrato, S. P. Monserrato-Sestu Km 0,700, 09042 Monserrato (CA), Italy e-mail: [giancarlo.cappellini;vincenzo.fiorentini]@dsf.unica.it
3
INFM - Sardinian Laboratory for Computational Materials Science (SLACS)
Received:
25
October
2004
Accepted:
8
November
2004
We present theoretical electron affinities, calculated
as total energy differences, for a large sample of polycyclic aromatic
hydrocarbons (PAHs), ranging in size from azulene (C10H8) to
dicoronylene (C48H20). For 20 out of 22 molecules under study
we obtained electron affinity values in the range 0.4-2.0 eV, showing
them to be able to accept an additional electron in their LUMO orbital.
For the mono-anions we computed the absolute photo-absorption cross-sections
up to the vacuum ultraviolet (VUV) using an implementation in real time and
real space of the Time-Dependent Density Functional Theory (TD–DFT), an
approach which has already been proven to yield accurate results for neutral
and cationic PAHs. Comparison with available experimental data hints
that this is the case for mono-anions as well. We find that PAH anions, like
their parent molecules and the corresponding cations, display strong
electronic transitions in the UV. The present results provide a quantitative
foundation to estimate the fraction of specific PAHs which can be singly
negatively charged in various interstellar environments, to simulate their
photophysics in detail and to evaluate their contribution to the interstellar
extinction curve.
Key words: astrochemistry / molecular data / molecular processes / ISM: molecules / ultraviolet: ISM / methods: numerical
© ESO, 2005
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