Fragmentation Energetics and Dynamics of the Neutral and Ionized Fluorobenzene·Ar Cluster Studied by Mass Analyzed Threshold Ionization Spectroscopy†

Abstract

Mass-analyzed threshold ionization spectroscopy (MATI) was used for a detailed investigation of the dissociation process of a fluorobenzene·Ar complex. The threshold ion spectra were recorded for the fluorobenzene monomer and the fluorobenzene·Ar complex by exciting the chromophore via different vibrational states of the S₁. The ion state spectra of the (fluorobenzene·Ar)⁺ cation exhibit significant progressions of the van der Waals bending mode b_x, which indicates a significant structural change of the complex upon ionization. The disappearance of the threshold ion signal for a certain excess energy in the complex (fluorobenzene·Ar)⁺ and the simultaneous appearance of the missing bands in the spectra of the fragment ion give an upper limit for the dissociation energy of the complex in the cationic state. In addition, one feature observed in the fragment ion spectrum of the complex recorded via exciting the S₁6b ¹ state reveals the relatively fast predissociation (<4 ns) of the complex, if the vibrational energy in the S₁ state exceeds the binding energy D₁ (D₁ < 302 cm^-1).