Molecular ionization–dissociation of fluoranthene at 266 nm: Energetic and dissociative pathways

Experimental studies have been carried out for nanosecond 266-nm laser-induced photoionization and dissociation of fluoranthene, C16H10 with pulse energies from 0.5 to 20 mJ using a time of flight mass spectrometer. The fragmentation patterns have been characterized and discussed with respect to the number of absorbed photons. They fall into three regimes. The first regime involves low energy processes, where the molecular parent ion promptly dissociates, resulting in the formation of CmHn+(m=11−15)CmHn+(m=11−15) by a process where up to two photons are absorbed. The second regime involves intermediate energy, where dissociative processes are activated by up to three-photon absorption and produce a second group of daughter ions: C10Hn+C10Hn+, C9Hn+C9Hn+, and C8Hn+C8Hn+. Finally, there is a third dissociative process, characterized by the absorption of up to four photons, producing C7Hn+C7Hn+, C6Hn+C6Hn+, C5Hn+C5Hn+, C4Hn+C4Hn+, and C3Hn+C3Hn+. Most of the detected ions are of the form CmHn+CmHn+ with m < n. Total deprotonation has also been observed. The mechanism proposed involves the dissociation of the parent ion, which then dissociates by different competitive channels. Helium, neon and argon were used as carrier gases (CG). A detailed discussion is presented regarding the use of He as the CG. The laser pulse intensity allows the absorption of up to nine photons, observed through the formation of multiply charged ions of some of the CG atoms.

► Molecular photoionization and photodissociation of fluoranthene is analyzed.
► Two-photon resonant absorption at 266 nm is the responsible by the molecular ionization.
► At intensities of 109–1010 W cm−2, processes resulting by the absorption up to four photons are observed.
► The total molecular photo-dissociation can follow two different ways mainly dominated by the acetylene loss.