Effects of aromatic molecules inside argon clusters on the formation of multiply charged atomic ions in moderately...

We report the effect of two molecular species, fluorene (C₁₃H₁₀, Fl) and 1, 3, 5-trichlorobenzene (C₆H₃Cl₃, 3ClB), embedded in atomic argon clusters, on the generation of multiply charged atomic ions (MCAIs) in moderately intense nanosecond laser fields at 532 nm. The near resonant-enhancement of two photon absorption in the two aromatic species produces only a few low charge state (+2) atomic ions in a neat molecular cluster, but the enclosure of the same cluster with layers of Ar can significantly increase the charge state of MCAIs. The yields of singly charged atomic ions from the molecular species, such as H⁺, C⁺, and Cl⁺, are positively correlated with the number of molecules inside the Ar cluster, but the yields of the MCAI and Ar⁺ demonstrate opposite behaviors. A higher number of aromatic molecules are actually detrimental to the production of Ar⁺ and MCAIs. The results of exponential fittings of the yields of MCAIs at different laser intensities reveal a systematic change for the exponent of Ar⁺: with increasing concentrations of 3ClB in Ar clusters, the exponent decreases and eventually reaches the same value as those of MCAIs. These results are consistent with our previous hypothesis that the formation mechanism of MCAIs may be different from that of singly charged species and that the strong resonance of Ar₃ ⁺ may play an important role in the overall energy absorption. Moreover, the effect of the molecular core seems to change the formation mechanism of Ar⁺ to that of MCAIs.