Laboratory Transition Frequencies for Millimeter‐Wave Lines of Vibrationally Excited HC 7 N

The carbon chain HC 7 N has been produced in the laboratory by gas-phase copyrolysis of phosphorus trichloride and 2-ethynyl-pyridine (C 7 H 5 N). 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 HC 7 N in low-lying vibrational states provides accurate rest frequencies useful for a possible identification of radio lines produced by vibrationally excited HC 7 N in hot core molecular sources and circumstellar shells.