High resolution vibration-rotation spectra of carbon suboxide: Molecular constants for the ground state and 2ν70

The infrared spectrum of C₃O₂ was recorded with the vacuum Fourier transform interferometer of Laboratoire Aimé Cotton at a resolution of 0.005 cm^?1. The ground state molecular constants were calculated from lower state combination relations in a simultaneous analysis of six ground state transitions situated in the region 3000 to 5000 cm^?1. Through the analysis of a difference band we established that $\text{2ν}{}_7{}^0$ is 60.7022 ± 0.0005 cm^?1 above the ground vibrational state. Accurate molecular constants were also determined for this vibrational level.