The low-lying quartet and doublet states of BN
+ are reinvestigated theoretically by using multireference CI wavefunctions with a 6s5p3d1f basis set. The X
4Σ
− ground state has a dissociation energy of 1.13 eV. The
first excited state is
2 Π (
Te = 0.59 eV), with 1
2Σ
− lying 0.11 eV higher. The infrared spectrum of X
4 Σ
− is characterized by very low absorption intensities (
I ![](/images/glyphs/BQ3.GIF)
8 km/mol for the fundamental absorption) and long emission lifetimes (4.9 s for
v = 1 →
v = 0). Franck-Condon factors, oscillator strengths (
fv′v″) and radiative lifetimes (τ
v′) of the quartet-quartet transitions A
4Π−X
4Σ
−, B
4Σ
−−X
4Σ
−, B
4Σ
−−A
4Π and C
4Π−X
4 Σ
− are given. The strongest absorption band corresponds to B
4Σ
−−X
4 Σ
−, with
T00 = 3.81 eV and
f00 = 0.0175. The longest lived quartet state is A
4Π, with τ
0 ![](/images/glyphs/BQ4.GIF)
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 X
3Π(BN) → X
4Σ
−(BN
+) is 11.4 eV. A separation of 13.87 eV between X
4Σ
−(BN
+) and X
2Σ
+(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 1
2Π state of BN
+.