THE LASER PHOTOELECTRON SPECTRUM OF GAS PHASE p-DIFLUOROBENZENE

Author Institution: Department of Chemistry, Indiana University; Department of Chemistry, Indiana University; Department of Chemistry, Indiana UniversityGas phase p-difluorobenzene (PDFB) has been ionized from several vibronic levels of the excited $^{1}B_{2u}$ electronic state via two photon, two color laser ionization. Kinetic energy analysis of the ejected photoelectrons indicates that ions are generated in their ground electronic state. The vibrational state distribution is dependent on the vibronic level from which ionization occurs. Analysis of vibrational structure in the photoelectron spectra identifies seven vibrational frequencies of the PDFB cation. In many cases band intensities reflect the presence of Fermi resonance which exists in the $^{1}B_{2u}$ state. Results also indicate that the ion is slightly nonplanar in its equilibrium geometry. When PDFB is ionized from high vibronic levels of the $^{1}B_{2u}$ state $(E_{yib} > 1600 cm^{-1})$, congestion occurs in the photoelectron spectra. This is interpreted as being due to severe vibrational state mixing which exists in the $^{1}B_{2u}$ state. This effect is also observed in a similar experiment when ionizing from vibronic levels of the $^{1}B_{2u}$ electronic state of benzene."