Photoelectron spectroscopy of pyrene anion clusters: autodetachment via excited states of anion and intermolecular interactions in anion clusters.

This study examined the anion clusters of pyrene (Py) by mass spectrometry, photoelectron spectroscopy, and theoretical calculations. The photoelectron spectra of Py(n)(-) (n=1-4) were obtained at various photon energies. A change in photodetachment wavelength resulted in a large change in the relative intensities of vibrational progression in the photoelectron spectra. It is proposed that the observed modulation of the Franck-Condon factors by the different photon energies reflects autodetachment via the excited states of anion. The photoelectron spectra of Py(n)(-) at 355 nm showed a broad band structure between the S(0) and T(1) states, which is also due to the autodetachment via a Feshbach resonance state. The photoelectron spectra of Py(2)(-) suggest the presence of a unique dimeric interaction between the two pyrene moieties, whereas the spectral features of Py(3)(-) are similar to those of Py(1)(-). The stable structures of Py(2)(-) and Py(3)(-) obtained by density functional theory calculations support the experimental findings, where different intermolecular interactions govern the stabilization of these two species.