High resolution threshold photoelectron spectroscopy of aniline and aniline van der Waals complexes

Zero electron kinetic energy threshold photoelectron spectroscopy is applied to jet cooled aniline and the van der Waals molecules aniline–Ar, aniline–(Ar)₂, and aniline–CH₄. The monomer cation spectrum is assigned and more precise values of the vibrational frequencies are determined. The spectra of the cation complexes reveal significant vibronic activity indicative of a significant change in complex geometry upon ionization. The change in complex binding energy upon ionization is obtained from a determination of the complex ionization potentials. For the first time zero electron kinetic energy is used to probe van der Waals complex predissociation on the S₁ electronic surface. Both reactants (complex) and products (monomer) of the reaction are observed in the photoelectron spectrum. Details of the mechanism of the zero electron kinetic energy threshold photoionization process and its impact on the observation of van der Waals molecules are discussed.