Rotational Spectra of the Nitrogen‐Sulfur Carbon Chains NC n S, n = 1–7

Abstract

Seven carbon chain radicals NC n S where n ¼ 1 7 have been detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Although NCCS is found to have a bent structure and an asymmetric top spectrum, the five longer chains have linear heavy-atom backbones, and like the isovalent HC n S chains, the electronic ground states of each alternate with even and odd numbers of carbon atoms: NC 4 S and NC 6 S have 2 P 1/2 ground states, while NC 3 S, NC 5 S, and NC 7 S have 2 P 3/2 ground states. In addi-tion, the lowest-rotational transitions of the NCS radical have been detected in both fine-structure levels in the same supersonic molecular beam source, allowing a precise determination of the ground state hyperfine coupling constants. The centimeter-wave spectra of NC 3 S and the four longer chains have been fully characterized, and spectroscopic constants, including those that describe the lambda-type doubling and hyperfine structure from the nitrogen nucleus, have been determined to high precision. A complete account of the centimeter-wave spectrum of NCCS will be given by Nakajima et al. Predicted properties from UQCISD/cc-pVDZ ab initio calculations are also reported for the NC n S chains up to NC 7 S. All six new chains are highly polar and all are plausible candidates for astronomical detection because C n S chains up to C 3 S and C n N chains up to C 5 N are detected in both interstellar and circumstellar sources.