57th Annual Report on Research 2012 Under Sponsorship of the ACS Petroleum Research Fund

Ultraviolet Spectroscopy of neat fluorobenzene and mixed benzene-fluorobenzene clusters. Neat fluorobenzene (F_n) and mixed benzene-fluorobenzene (B_mF_n) clusters were interrogated via resonant two photon ionization (R2PI) spectroscopy. One-color spectra were collected through fluorobenzene's B₂ ← A₁ 0⁰₀ vibronic transition at 37813 cm^-1 over a spectral shift ranging from -200 cm^-1 to +80 cm^-1 (relative to 37813 cm^-1). [Spectra and related graphics are presented in the report nugget.] Artifacts originating from fragmentation were cleaned from the dimer by subtracting ~1/3 of the trimer spectrum intensity. Analysis suggests the presence of four van der Waals progressions in the dimer spectrum, with fundamental frequencies of 4.1, 6.1, 14.6, and 16.2 cm^-1 respectively. The sharp features observed in the ultraviolet spectrum are hypothesized to originate from two distinct F₂ isomers, each having two separate van der Waal's modes with transitions near 5 and 15 cm^-1 respectively. Analysis of the trimer spectra is in progress.

Electronic structure calculations of dimer clusters. To better understand the observed spectral features, electronic structure calculations are underway for the F₂ and BF dimer clusters. Three distinct method/basis set combinations are being applied for the purpose of identifying consensus structures, relative energies, and frequencies. When analysis is complete, results are expected to confirm the frequencies and characteristics of the van der Waals modes and to identify the primary dimer structures present in the experimental supersonic expansion.