Knowledge Bank

The rotational spectra of C$3$N$-$, C$4$H$-$, and C$4$D$-$ have been observed at high spectral resolution by Fourier transform microwave spectroscopy. For both C$3$N$-$and C$4$D$-$, frequencies of the hyperfine components in the lowest-$J$ transitions have been determined to better than 0.1 ppm. The derived quadrapole coupling constants $eQq$ for both anions are in good agreement with theoretical predictions. A number of other properties of these anions, including linewidths and rotational temperatures, have been systematically studied with respect to similar-sized neutral molecules. The production of C$4$H$-$ using different hydrocarbon precursor and buffer gases has also been investigated.