Cyanooxomethylium, NCCO+, a fundamental linear acylium ion, has been observed spectroscopically for the first time using action spectroscopy in ion trap apparatuses. A first low-resolution infrared spectrum was obtained between 500 to 1400 cm−1 and 2000 to 2500 cm−1 using the Free Electron Laser for Infrared eXperiments (FELIX) and the FELion apparatus, employing infrared predissociation of the weakly bound NCCO+-Ne complex. Subsequently, high-resolution studies of the bare ion were performed with the COLtrap II setup, one targeted at the CN-stretching mode ν2 around 2150 cm−1 using leak-out spectroscopy and one at the pure rotational spectrum employing a leak-out infrared/millimeter-wave double resonance approach covering transition frequencies as high as 246 GHz. Spectroscopic detection and analysis were guided by high-level quantum-chemical calculations performed at the CCSD(T) level of theory. The collected data permit accurate frequency predictions to support future astronomical searches with sensitive radio telescopes.
@article{arxiv.2601.20365,
title = {Spectroscopic Detection and Characterization of Cyanooxomethylium, NCCO$^+$},
author = {Marcel Bast and Julian Böing and Thomas Salomon and Eline Plaar and Igor Savić and Mathias Schäfer and Oskar Asvany and Stephan Schlemmer and Sven Thorwirth},
journal= {arXiv preprint arXiv:2601.20365},
year = {2026}
}