A combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of BCl₃

The pulsed field ionization-photoelectron (PFI-PE) spectrum of boron trichloride (BCl₃) in the region of 93 590-95 640 cm^-1 has been measured using vacuum ultraviolet (VUV) laser. At energies 0-1100 cm ^-1 above the adiabatic ionization energy (IE) of BCl₃, the bending vibration progression of BCl₃⁺ is clearly resolved in the PFI-PE spectrum, whereas the spectrum at energies 1200-1900 cm^-1 above the IE(BCl₃) is found to exhibit dense vibrational structure. This observation unambiguously shows that BCl₃⁺ in its ground state has C_2v symmetry. Ab initio calculations performed at the CCSD(T)/CBS level with high-level corrections are consistent with this observation, indicating that the BCl ₃⁺(X̃ ²B₂) ground state has two long and one short B-Cl bonds. Furthermore, the CCSD(T)/CBS calculations predict the existence of two BCl₃⁺ transitional structures with D_3h and C_2V symmetries lying ≈800 and 1300 cm^-1, respectively, above the BCl₃⁺(X̃ ²B₂) ground state. This prediction is also consistent with the dense features observed in the PFI-PE spectrum in the region of 1200-1900 cm^-1 above the IE(BCl₃). The assignment of the PFI-PE vibrational bands gives the IE(BCl₃) = 93 891 ± 2 cm ^-1 (11.6410 ± 0.0003 eV) and the bending frequencies for BCl₃⁺(X̃ ²B₂), v₁⁺(b₂) = 194 cm^-1 and v₁⁺(a₁) = 209 cm^-1. We have also examined the dissociative photoionization process BCl₃ + hv → BCl₂⁺ + Cl + e^- using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy (AE) for this process to be 12.495 ± 0.002 eV. Combining this 0 K AE value and the IE(BCl₃), we have determined the 0 K bond dissociation energy (D₀) for Cl₂B⁺-Cl as 0.854 ± 0.002 eV. This experimental and theoretical study indicates that the CCSD(T, Full)/CBS calculations with high-level corrections are highly reliable for the predictions of IE(BCl₃), AE(BCl₂⁺) and D₀(Cl₂B⁺-Cl) with error limits of less than 35 meV. However, the CCSD(T, Full)/CBS predictions for ΔH_f0° (BCl₃), ΔH_f0°(BCl₂⁺), and ΔH_f0°(BCl₃⁺) are less reliable with discrepancies up to 0.1 eV as compared to the experimental determinations. © The Owner Societies 2005.