Infrared action spectroscopy of fundamental nitrilium ions: Protonated vinyl- and ethyl cyanide

Infrared action spectra of the protonated forms of two fundamental organic nitriles, vinyl cyanide, C2H3CN, and ethyl cyanide, C2H5CN, have been observed using the FELion 22-pole ion trap apparatus and the Free Electron Laser for Infrared eXperiments (FELIX) at Radboud University, Nijmegen (The Netherlands). Vibrational bands of both ions were observed in the wavenumber regime between 300 and 2500 cm(-1) and spectroscopically assigned based on results from anharmonic force field calculations performed here at the coupled cluster level of theory. As the action spectroscopy scheme used in the present study probes the Ne-tagged weakly bound complexes, C2H3CNH+-Ne and C2H5CNH+-Ne, corresponding quantum-chemical calculations of these systems were also performed. Significant blueshifts observed for the strong-CNH+ bending modes indicate that the neon atom is attached to the proton bound to the nitrile group in both molecular ions.