  A novel theoretical method is developed to study the polycyclic aromatic
hydrocarbon - diffuse interstellar band (PAH-DIB) hypothesis. In this method, a
computer program is used to enumerate all PAH molecules with up to a specific
number of fused benzene rings. Fast quantum chemical calculations are then
employed to calculate the electronic transition energies, oscillator strengths,
and rotational constants of these molecules. An electronic database of all PAHs
with up to any specific number of benzene rings can be constructed this way.
Comparison of the electronic transition energies, oscillator strengths, and
rotational band contours of all PAHs in the database with astronomical spectra
allows one to identify possible individual PAH carriers of some of the intense
narrow DIBs. Using the current database containing up to 10 benzene rings we
have selected 8 closed-shell PAHs as possible carriers of the intense
lambda6614 DIB.
