Infrared Photodissociation Spectroscopy of C N , C N and C N.

The gas-phase vibrational spectroscopy of cold C N (n=2-4) anions is investigated in the CC and CN multiple bond stretching region (1700-2250 cm ) by means of infrared photodissociation (IRPD) spectroscopy in a cryogenically cooled ion trap of the corresponding messenger-tagged complexes. The IRPD spectra are assigned to N-terminated linear structures with triplet ground states ( Σ ) based on a comparison with harmonic vibrational frequencies and intensities from density functional theory computations. In contrast to the polyacetylenic C N anions, the linear C-C chains investigated here exhibit cumulenic character, which is most pronounced in C N and decreases with chain length. Additional intense transitions are observed for C N above 3000 cm and are attributed to overtone and combination bands involving the CC stretching modes, based on anharmonic computations. The influence of a D tag on the vibrational features of C N anions is shown to be small.