Zero Kinetic Energy Photoelectron Spectroscopy of Pyrene

Abstract

We report zero kinetic energy photoelectron (ZEKE) spectroscopy of pyrene via resonantly enhanced multiphoton ionization. Our analysis centers on the symmetry of the first electronically excited state (S(1)), its vibrational modes, and the vibration of the ground cationic state (D(0)). From comparisons between the observed vibrational frequencies and those from ab initio calculations at the configuration interaction singles level using the 6-311G (d,p) basis set, and based on other previous experimental and theoretical reports, we confirm the (1)B(2u) symmetry for the S(1) state. This assignment represents a reversal in the energy order of the two closely spaced electronically excited states from our theoretical calculation, and extensive configuration interactions are attributed to this result. Among the observed vibrational levels of the S(1) state, three are results of vibronic coupling due to the nearby second electronically excited state. The ZEKE spectroscopy obtained via the vibronic levels of the S(1) state reveals similar modes for the cation as those of the intermediate state. Although we believe that the ground ionic state can be considered a single electron configuration, the agreement between theoretical and experimental frequencies for the cation is limited. This result is somewhat surprising based on our previous work on cata-condensed polycyclic aromatic hydrocarbons and small substituted aromatic compounds. Although a relatively small molecule, pyrene demonstrates its nonrigidity via several out-of-plane bending modes corresponding to corrugation of the molecular plane. The adiabatic ionization potential of neutral pyrene is determined to be 59 888 ± 7 cm(-1).

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

“…The adiabatic ionization energy (IE) of neutral pyrene was determined to be 59888 cm −1 (7.425 eV), 47 so the molecule can be ionized in a [1+1]…”

Theoretical Study on Molecules of Interstellar Interest. II. Radical Cation of Compact Polycyclic Aromatic Hydrocarbons

“…37 The uncoupled X state spectrum is calculated by the matrix diagonalization scheme using only low-frequency totally-symmetric vibrational modes. From the theoretical data observed peaks at ∼416 and ∼592 cm −1 are assigned to the fundamental of ν 13 and ν 12 vibrational modes, respectively.…”

“…Very recently ZEKE and multiphoton ionization spectra of Py are recorded by Kong et al 37 These authors examined the spectral progressions and pointed out the importance of vibronic coupling. Except some electronic structure calculations, [38][39][40][41][42][43][44] a detailed theoretical study is not carried out on this molecules until now.…”

Cation spectroscopy of 3,4-difluoroaniline by two-color resonant two-photon mass-analyzed threshold ionization

“…However, the ionization energy (IE) and spectroscopic information of this molecule in the cationic state are still not available in the literature. One may use laser-induced fluorescence [14] and zero-kinetic energy (ZEKE) photoelectron spectroscopy [15,16] to record the vibronic and cation spectra of molecules. It is known that the resonance-enhanced multi-photon ionization [17] and mass-analyzed threshold ionization (MATI) [18] techniques involve the detection of ions and can provide similar spectroscopic information.…”