Photoelectron spectroscopy of boron-containing reactive intermediates using synchrotron radiation: BH₂, BH, and BF

Mass selected slow photoelectron spectra (SPES) of three boron-containing reactive species, BH₂, BH, and BF were recorded by double imaging photoion–photoelectron coincidence spectroscopy (i²PEPICO) using synchrotron radiation. All species were generated in a flow reactor from the H-abstraction of B₂H₆ by F atoms created in a F₂ microwave discharge. The spectrum of BH₂⁺ exhibits a long bending mode progression with a 970 cm⁻¹ spacing due to the large geometry change from bent to linear upon ionization. Its ionization energy was determined as 8.12 ± 0.02 eV. For BH, photoionisation from both X¹Σ⁺ singlet and a³Π triplet state was observed, permitting the experimental determination of the singlet/triplet gap (ΔE_ST) from the observed IE's of 9.82 eV and 8.48 eV. In addition, a threshold photoelectron spectrum of BF was recorded, which leads to an IE of 11.11 eV and an improved value for ν_BF⁺ of 1690 cm⁻¹. All spectra were simulated by calculating Franck–Condon factors from optimised structures based on quantum chemical calculations.