High-level ab initio quartic force fields and spectroscopic characterization of C₂N⁻

Abstract

By relying on a high-level composite energy scheme, we report accurate quartic force fields and spectroscopic attributes for C2N−. The results are expected to trigger future laboratory and astronomical line surveys on this nitrile anion.

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

“…[24] with data from Garand et al [23] and Muzangwa et al [45] . We could assign the bands with high‐level VCI calculations, supported by previous VAR calculations [24] …”

“…The $${\nu _{{\rm{C}} - {\rm{CN}}} }$$ stretch vibration ( ν 3 ) is predicted to be at at 1058 cm −1 by our VCI calculations and at 1045.8 cm −1 by Rocha and Linnartz [24] . We did not detect a band in the range from 933 to 1203 cm −1 .…”

“…This value is in good agreement with the anharmonic frequency of 452 cm −1 obtained from our VCI calculations based on a multi‐mode PES with up to 3‐mode coupling at the CCSD(T)‐F12/cc‐pVTZ−F12 level of theory. Assigning this vibrational band to the $${\delta _{{\rm{CCN}}} }$$ ( ν 2 ) bending vibration is additionally supported by the accurate state‐of‐the‐art rovibrational quantum chemical calculations from Rocha and Linnartz, [24] determining ν 2 to be at 452.1 cm −1 using variational DVR3D calculations.…”

“…The C n N − anion can be treated as a linear system [21] in the $${C_{\infty v} }$$ point group, with the electronic ground state being a singlet ( 1 Σ) for the CN − and C 3 N − species and a triplet ( 3 Σ) for the C 2 N − species. Note that also non‐linear geometries and different electronic states were studied for C 2 N − , [24] while for C 3 N − only linear constitutional isomers have been considered [53] . The hydrogen molecule H 2 is weakly bound to the C n N − anion and considered as a messenger molecule or tag .…”

“…For C 2 N − the authors assigned the fundamental bending vibration. Up to now, further spectroscopic signatures were only theoretically predicted by Rocha and Linnartz [24] . They performed extensive anharmonic calculations for C 2 N − and CNC − using vibrational perturbation theory of second order (VPT2) to solve the three‐atom rovibrational Hamiltonian by discrete variable representation (DVR3D) [25] .…”