FTMW spectroscopy of the NC2O and NC3O radicals and ab initio calculations

Rotational transitions of the carbon-chain radicals, NC 2 O and NC 3 O, have been observed for the first time by Fourie-transform microwave spectroscopy. The radicals were produced in a supersonic free jet by a pulsed discharge of acetylcyanide (CO(CH 3 )(CN)) diluted in Ar for NC 2 O or a gas mixture of HC 3 N and O 2 diluted in Ar for NC 3 O. Pure rotational transitions from N =1–0 to N =3–2 for NC 2 O and those from N =2–1 to N =6–5 for NC 3 O, both with fine and hyperfine structures, were observed. The rotational, spin-rotation, and hyperfine coupling constants for the radicals have been precisely determined. Ab initio calculations at the RCCSD(T) level of theory considering the correlation of core electrons using the cc-pCVTZ basis sets have been performed. The present observations and the ab initio calculations revealed that both the radicals have bent structures in the ground states.