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Abstract:
The gas-phase vibrational spectroscopy of cold C2nN− (n=2–4) anions is investigated in the CC and CN multiple bond stretching region (1700–2250 cm−1) 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 (3Σ−) based on a comparison with harmonic vibrational frequencies and intensities from density functional theory computations. In contrast to the polyacetylenic C2n+1N− anions, the linear C−C chains investigated here exhibit cumulenic character, which is most pronounced in C4N− and decreases with chain length. Additional intense transitions are observed for C6N− above 3000 cm−1 and are attributed to overtone and combination bands involving the CC stretching modes, based on anharmonic computations. The influence of a D2 tag on the vibrational features of C2nN− anions is shown to be small.
