An ab initio investigation of the infrared and visible-UV spectra of BN+, and photoionization spectrum of BN Original Research Article

The low-lying quartet and doublet states of BN+ are reinvestigated theoretically by using multireference CI wavefunctions with a 6s5p3d1f basis set. The X4Σ− ground state has a dissociation energy of 1.13 eV. The first excited state is 12π (Te = 0.59 eV), with 12Σ− lying 0.11 eV higher. The infrared spectrum of X4Σ− is characterized by very low absorption intensities (I ≌ 8 km/mol for the fundamental absorption) and long emission lifetimes (4.9 s for ν = 1 → ν = 0). 7Franck-Condon factors, oscillator strengths (fν′ν″) and radiative lifetimes (τν′) of the quartet-quartet transitions A4Π-X4Σ−, B4Σ−-X4Σ−, B4Σ−-A4Π and C4Π-X4Σ− are given. The strongest absorption band corresponds to B4Σ−-X4Σ− with T00 = 3.81 eV and τ00 = 0.0175. The longest lived quartet state is A4Π, with τ0 ≈ 21 μs. The lifetimes of the B and C states (25 and 60 ns) are controlled by direct decay into the ground state rather than by cascading processes. The best estimate for the adiabatic ionization potential X3Π(BN) → X4Σ−(BN+) is 11.4 eV. A separation of 13.87 eV between X4Σ−(BN+) and X2Σ+(BN−), calculated at Re(BN+), agrees well with 13.8 ± 0.3 eV determined by charge inversion spectrometry. Finally, a model photoionization spectrum of BN is proposed to assist in the experimental characterization of the ground state of BN (whether 3Π or 1Σ+) via the 12Π state of BN+.