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Astron. Astrophys. 319, 331-339 (1997)

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3. Search for the fluorescence of C20 H [FORMULA]

Encouraged by the recent results of Joblin et al. (1995) in rare-gas matrices, we have looked for the fluorescence of the perylene cation using the LIF technique. The absorption spectrum of the perylene cation in a neon matrix shows two main bands near 525 and 730 nm. In matrices, the fluorescence signal is detected at longer wavelengths mostly in two bands near 790 and 810 nm. We tuned the dye laser on the 730 nm-band and thoroughly searched for fluorescence in a large domain (50 nm wide) centered at 800 nm but failed to observe the signal reported by Joblin et al. (1995).

The reasons of this non-detection may be:
(i) the excimer excitation forms few cations or perylene cations recombine efficiently, leaving preferentially neutral fragments,
(ii) the fluorescence quantum yield of the perylene cation in the gas phase is much lower than in matrices,
(iii) the emission observed by Joblin et al. (1995) is phosphorescence rather than fluorescence while our experiment acquiring signal on short timescales (a few µsec) is weakly sensitive to phosphorescence.
(iv) the species emitting in the matrix (Joblin et al. 1995) is not the perylene cation and this alternate species is pumped by energy transfer.

We do not have material to sort within these possibilities. Nonetheless we think that (ii) is more probable and (iv) is less probable.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998