Laboratory transition frequencies for millimeter-wave lines of vibrationally excited HC7N

The carbon chain HC7N has been produced in the laboratory by gas-phase copyrolysis of phosphorus trichloride and 2-ethynyl-pyridine (C7H5N). Its rotational spectrum has been investigated in the millimeter-wave region for the ground state and for five vibrationally excited states that lie below 300 cm(-1), namely, (v(13), v(14), v(15)) (0, 0, 1), (0, 0, 2), (0, 0, 3), (0, 1, 0), and (1, 0, 0). Transitions up to J=201<--200 were observed for the ground vibrational state, reaching a frequency as high as 230 GHz. The laboratory assignment of the rotational spectra of HC7N in low-lying vibrational states provides accurate rest frequencies useful for a possible identification of radio lines produced by vibrationally excited HC7N in hot core molecular sources and circumstellar shells.