Rotational Spectra of the Nitrogen-Sulfur
Carbon Chains NCnS, n=1-7
M. C. McCarthy, A. L. Cooksy, S. Mohamed, V. D. Gordon, and P. Thaddeus
Harvard-Smithsonian Center for Astrophysics
Department of Chemistry, San Diego State University
Abstract
Seven carbon chain radicals NCnS where n=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 HCnS chains, the electronic states of each alternate
with even and odd number of carbon atoms: NC4S and NC6S have
2Pi1/2 ground states, while NC3S, NC5S, and NC7S have 2Pi3/2 ground states.
In addition, 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, 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 NCnS chains
up to NC7S. All six new chains are highly polar and all are plausible
candidates for astronomical detection because CnS chains up to C3S
and CnN chains up to C5N are detected in both interstellar and
circumstellar sources.