Spectra of HC 3 N were collected at 300 K and 20 K to determine the ro-vibrational band center, assign J states, and refine rotational constants. Large spectral surveys were first obtained by scanning the probe laser linearly from 6555 to 6548 cm -1 with a step size of ∼ 0.001 cm -1 . These larger survey scans were used to identify approximate peak centers of the 2ν 1 transition, make initial J state assignments, and identify possible hot bands. Figure shows the resulting spectral surveys for both temperatures. Due to the long scan times needed to collect the full spectrum (over 20 hours), instrument drift inevitably led to fluctuations in the peak intensities, which should not be taken to be accurate in the survey scans.