The S₀ → S₁ cavity ring-down absorption spectrum of jet-cooled azulene: Dependence of internal conversion on the excess energy

The S₀ → S₁ cavity ring-down (CRD) absorption spectrum of jet-cooled azulene is reported in the spectral region between 14 275 and 17 300 cm^-1. The excess energy dependence of the fast internal conversion rate k(ic) (S₁ → S₀) was investigated in the frequency domain by evaluating the linewidths of vibronic states up to excess energies of ~hc x 2500 cm^-1. A value for the S_1,0 lifetime of ≃ 2.6 ± 0.4 ps was found. New experimental evidence for a conical intersection of the S₀ and S₁ potentials at ≃ 2100 ± 100 cm^-1 was found. The possibility of azulene being one of the carriers of the diffuse interstellar bands (DIB) is briefly discussed.