Binding energies and dissociation pathways in the aniline-Ar2 cation complex.

Mass analyzed threshold ionization spectroscopy is used to measure the Ar binding energy for the cationic aniline-Ar (An(+)-Ar) and aniline-Ar(2) (An(+)-Ar(2)) complexes. Since the experiments begin with the neutral species, photoexcitation creates the cations in the pi-bonding configuration with the Ar located above the phenyl ring. The binding energy in this conformation of the An(+)-Ar complex is determined to be 495+/-15 cm(-1). Measurements of An(+)-Ar(2) revealed the production of a lower energy dissociation product which is assigned to the An(+)-Ar H-bonding configuration. Combinations of measurements allow determination of the dissociation energy of this complex to be 640+/-20 cm(-1). The observation of a more stable H-bonded conformer is consistent with recent infrared experiments on An(+)-Ar complexes created by complexing An(+) with Ar, rather than creation through the neutral complex. Calculations are presented which closely reproduce the binding energy of the pi bound Ar but underestimate the stability of the H-bonded species.