Electronic and vibrational spectroscopy of benzonitrile cation for astrochemical consideration

The electronic and vibrational spectra of benzonitrile cation, C₆H₅CN⁺ (BZN⁺), in the gas phase at low temperatures are reported. Measurements were carried out using a cryogenic ion trapping apparatus. The mid-infrared spectrum shows a strong CN stretch at 2130 ± 1 cm⁻¹ (4.694 ± 0.002 µm). The electronic spectrum is reported in the range 5040-5750 Å. This covers the forbidden B²B₂ ← X²B₁ and allowed C²B₁ ← X²B₁ transitions. The spectrum is dominated by a broad absorption feature at wavelengths shorter than 5250 Å, with the strongest absorption located at 5140 Å. Experimental data are complemented with quantum chemical calculations carried out at the density functional theory and extended multi-configurational quasi-degenerate perturbation theory level. The spectroscopic results are discussed in the context of astronomical observations in the infrared and visible.