Vibrational Predissociation Spectra of C2 N- and C3 N- : Bending and Stretching Vibrations

Abstract

We present infrared predissociation spectra of C₂ N^- (H₂ ) and C ₃ N^- (H₂ ) in the 300-1850 cm^-1 range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C₂ N^- (H₂ ), we detected the CCN bending and CC-N stretching vibrations. For the C₃ N^- (H₂ ) system, we detected the CCN bending, the CC-CN stretching, and multiple overtones and/or combination bands. The assignment and interpretation of the presented experimental spectra is validated by calculations of anharmonic spectra within the vibrational configuration interaction (VCI) approach, based on potential energy surfaces calculated at explicitly correlated coupled cluster theory (CCSD(T)-F12/cc-pVTZ-F12). The H₂ tag acts as an innocent spectator, not significantly affecting the C_2,3 N^- bending and stretching mode positions. The recorded infrared predissociation spectra can thus be used as a proxy for the vibrational spectra of the bare anions.