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

Abstract

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 C2v symmetry. Ab initio calculations performed at the CCSD(T)/CBS level with high-level corrections are consistent with this observation, indicating that the BCl3+(X 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 D3h and C2v symmetries lying 800 and 1300 cm(-1), respectively, above the BCl3+ (X 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 (11.6410 +/- 0.0003 eV) and the bending frequencies for BCl3+ (X 2B2), v1+ (b2) = 194 cm(-1) and v1+ (a1) = 209 cm We have also examined the dissociative photoionization process BCl3 + hu --> 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 (BCI2+) and D0 (Cl2B(+) -Cl) with error limits of less than 35 meV. However, the CCSD (T, Full)/CBS predictions for deltaH(f0) degrees (BCl3), deltaH(f0) degrees (BCl2+), and deltaH(f0)degrees (BCl3+) are less reliable with discrepancies up to 0.1 eV as compared to the experimental determinations.