Electronic Structure of the BF₂ Radical Determined by ab Initio Calculations and Resonance-Enhanced Multiphoton Ionization Spectroscopy

Abstract

We report the first electronic absorption spectrum of the boron difluoride radical. This spectrum appeared in mass-selected multiphoton ionization spectra between 235 and 420 nm. Strong bent−linear structure changes prevented observations of electronic origin bands. EOM-CCSD ab initio calculations suggest that the observed vibrational bands arise from Ã2B1 ← X̃ 2A1 (T vert = 35 100 cm-1) one-photon absorption and from B̃ 2A1 (3s) ←← X̃ 2A1 (T vert = 59 100 cm-1) and C̃ (3p) ←← X̃ 2A1 (T vert = 63 100 cm-1) two-photon transitions. Ab initio calculations predicted the geometries and vibrational frequencies of the ground states of the BF2 radical, cation, and anion. Ab initio calculations also predicted the vertical transition energies to the excited electronic states from the ground state radical. QCISD(T) calculations estimate ionization potentials for BF2 radicals of IPa = 8.66 eV and IPv = 10.44 eV and adiabatic and vertical electron detachment energies for BF2 - of EA = 1.14 eV and VDE = 1.64 eV. We estimate these ionization and detachment energies to be reliable to about 0.05 and 0.10 eV, respectively.

Electron scattering studies of BF and BF2

“…The absolute ground state energy obtained with this model is -223.7094 Hartree, which is in reasonable agreement with the ground state energy of Cai [45] at -224.0715 Hartree. The first excitation energy of BF 2 is reported at 6.44 eV with the present target model and is quite high with respect to the data of Cai [45] and Atkinson et al [46] at 3.24 and 4.66 eV respectively. For both BF and BF 2 the vertical excitation energies are in general higher than other values.…”

Rate Coefficients for the Propargyl Radical Self-Reaction and Oxygen Addition Reaction Measured Using Ultraviolet Cavity Ring-down Spectroscopy

“…Propargyl concentrations were monitored using a recently developed laser photolysis/cavity ring-down apparatus. 10 Previously reported 11 and confirmed 12 UV absorption bands were used to monitor the propargyl radical concentration during the kinetic measurements. These studies used kinetic data produced by three different photolytic precursors of propargyl radical.…”

“…We note that CRD absorbance measurements have been demonstrated to obey the Beer-Lambert relationship for the broad transitions often encountered in the UV. 10 Cavity ring-down measurements observe the decay rate (β) of photon intensity in a stable optical cavity. Optical absorbance is computed from the difference between the decay rates β abs , the decay rate in the presence of an absorber, and β base , the base decay rate under nonabsorbing conditions.…”

The infrared spectra of BF3+ and BF2OH+ trapped in solid neon

“…The resulting structure approaches that for BF 2 + in a weakly bound complex with the remaining F atom. The calculations by Atkinson and co-workers 28 indicate that the ionization of BF 2 to BF 2 + shortens the two BF bond lengths from 1.32 Å to 1.23 Å and increases the FBF valence angle from 121.3 • to 180 • . The calculated position for ν 3 of 11 BF 2 + is 2055 cm −1 .…”

“…The ν 3 vibrational fundamental and the ν 2 + ν 4 combination band, both of e symmetry, are sufficiently close to make Fermi resonance interaction between those two energy levels probable. QCISD(T)/6-311+G* calculations by Atkinson and coworkers 28 yielded an adiabatic electron affinity of 1.14 eV for BF 2 and a vertical detachment energy of 1.64 eV for BF 2 − . Their B3LYP calculations using the same basis set yielded values that are ∼0.15 eV smaller.…”