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This project is focused on the study of organometallic reactive intermediates using matrix isolation and gas-phase spectroscopy.  In the first award period, we have constructed our matrix isolation apparatus and developed a pulsed jet discharge source for the production of metal containing intermediates.  Our first demonstration of this source, carried out on the known CF₂Br⁺ ion, demonstrated the advantages of the method.  Thus, photolysis of a CF₂Br₂:Ar (~1:5000) sample at ~5 K produced primarily iso-CF₂Br₂ and CF₂ (+ Br₂) products, due both to facile recombination in the matrix cage and efficient secondary photolysis of the CF₂Br radical.  In contrast, the discharge sampled matrix spectrum shows strong absorptions due to CF₂Br and CF₂, as well as CF₂Br⁺.  The C-Br stretching frequency of this ion was determined for the first time, and building upon this success, the spectrum of CH₂Br⁺ was then observed by discharging CH₂BrX:Ar (X = I, Br) samples.  These results indicated that the primary mechanism for ion formation in the discharge is ionization/fragmentation of the parent by reaction with metastable rare gas atoms.

In collaboration with the groups of Alexander Tarnovsky (Bowling Green) and Bruce Ault (Cincinnati), studies of the matrix photochemistry of the halocarbons CF₂X₂ (X=Br, I) were initiated.   In this work, the iso-forms of these molecules were characterized for the first time, both experimentally and computationally.  Thus, photolysis of CF₂Br₂:Ar samples (~1:5000) held at ~ 5 K yielded the weakly bound iso-CF₂Br₂ (F₂CBr-Br) species.  Calculations at the CCSD(T)//MP2/aug-cc-pVTZ level show that the iso-form is a minimum on the CF₂Br_2­ potential energy surface. Iso-CF₂Br₂ is an intermediate in the Br + CF₂Br -> :CF₂ + Br₂ reaction, which has implications for a roaming pathway that has recently been invoked to explain the small yield of nascent Br₂ in gas-phase experiments.  Very recently, we have shown through detailed calculations and modeling of CF₂Br₂ and related systems that isomerization is a key pathway to molecular products in halon decomposition in the gas-phase.

Following our observation of the C₂H₄LBr₂ complex as a primary photoproduct in the photolysis of matrix isolated 1,2-dibromoethane, where the charge transfer band of the complex was observed for the first time, we developed a new dual–nozzle late–mixing scheme that is generally applicable for the trapping and interrogation of pre-reactive donor-acceptor complexes and will be used in studies of metal-containing intermediates.  This scheme was used initially to examine photoinduced electron transfer in this prototypical Mulliken donor-acceptor (halogen bonded) π-complex.  Excitation into the intense charge transfer band of the complex leads exclusively to the anti-conformer of the single reaction product, 1,2-dibromoethane, in agreement with the Mulliken theory of electron transfer.

In initial gas-phase studies of metal-containing intermediates using our pulsed discharge source, we have recently examined the Nickel monohalides, starting with NiI and more recently NiBr and NiCl.  Laser induced fluorescence and single vibronic level emission spectroscopy has been used to probe five low-lying electronic states that arise from the 3d⁹ configuration of Ni⁺.  Term energies and a complete set of vibrational parameters were derived for all five electronic states for NiX (X=Cl, Br, I), which afforded a detailed analysis of periodic trends in the Nickel monohalide series.  We are presently searching for small polyatomic intermediates containing nickel, including the hydroxide and metal carbene.