Spectroscopic Detection and Characterization of Cyanooxomethylium, NCCO$^+$

TL;DR

This study reports the first spectroscopic detection of the linear acylium ion NCCO$^+$ using various infrared and microwave techniques, supported by quantum-chemical calculations, enabling future astronomical identification.

Contribution

First spectroscopic observation and characterization of NCCO$^+$ using multiple high-resolution methods and quantum calculations.

Findings

Infrared spectrum obtained between 500-1400 and 2000-2500 cm$^{-1}$.

High-resolution rotational spectrum measured up to 246 GHz.

Quantum calculations accurately predicted frequencies for future searches.

Abstract

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 $\nu_2$ 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.