Knowledge Bank

The isoelectronic pair of radicals 2,4,6-heptatriynyl, $H2C-C\equiv C-C\equiv C-C\equiv C-H$, and 2,4-hexadiynylnitrile, $H2C-C\equiv C-C\equiv C-C\equiv N$, were produced in a pulsed discharge supersonic jet and detected by Fourier transform microwave spectroscopy. Seven rotational transitions of the heptatriynyl radical from $N\prime =4$ to 10 and six rotational transitions of the hexadiynyl-nitrile radical from $N\prime =4$ to 9 in the $Ka=0$ ladder were observed between 6 and 17 GHz. For each species, over 50 hyperline components were measured and assigned with an uncertainty of 5 kHz. Precise rotational, centrifugal distortion, spin-rotation, and various hyperfine coupling constants were determined for both $H2C7H$ and $H2C6N$.