Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theoretical evaluation of PAH dications properties   Aims. We present a systematic theoretical study on 40 polycyclic aromatic
hydrocarbons dications (PAHs++) containing up to 66 carbon atoms. Methods. We
performed our calculations using well established quantum-chemical techniques
in the framework of the density functional theory (DFT) to obtain the
electronic ground-state properties, and of the time-dependent DFT (TD-DFT) to
evaluate the excited\textendash state properties. Results. For each PAH++
considered we computed the absolute visible-UV photo-absorption cross-section
up to about 30 eV. We also evaluated their vibrational properties and compared
them to those of the corresponding neutral and singly-ionised species. We
estimated the adiabatic and vertical second ionisation energy DeltaI through
total energy differences. Conclusions. The DeltaI values obtained fall in the
energy range 8-13 eV, confirming that PAHs could reach the doubly-ionised state
in HI regions. The total integrated IR absorption cross-sections show a marked
increase upon ionization, being on the average about two and five times larger
for PAHs++ than for PAHs+ and PAHs, respectively. The visible-UV
photo-absorption cross-sections for the 0, +1 and +2 charge-states show
comparable features but PAHs++ are found to absorb slightly less than their
parent neutrals and singly ionized species between ~7 and ~12 eV. Combining
these pieces of information we found that PAHs++ should actually be more stable
against photodissociation than PAHs and PAHs+,_if_ dissociation tresholds are
nearly unchanged by ionization.

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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: math
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: physics
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The categories of this paper are: q-alg