Interactions between vibrational polyads of propyne, H3CCCH: Rotational and rovibrational spectroscopy of the levels around 1000 cm−1

The study of vibration resonance physics in propyne is based on experimental measurements of about 600 new rotational transitions between 495-590 and 700-760 GHz in excited vibrational levels v5 = 1, v8 = 1, v10 = 3 and v9 = v10 = 1 with vibrational energies around 1000 cm−1. The limits to the assignments and analysis were imposed by as yet unresolved anharmonic resonances with the states of the next higher polyad of levels lying above 1200 cm−1, which affect the rotational states involved in transitions that would be measurable with non-vanishing intensities. Vibration-rotation spectra pertaining to the levels in question were studied in the regions 880-1150 cm−1 (the ν5 and ν8 fundamental bands), 550-750 cm−1 (the v9 = v10 = 1 ← v10 = 1 hot bands) and 250-400 cm−1 (the v10 = 3 ← v10 = 2 “superhot” bands). A simultaneous least-squares fit of both types of data provides their reliable but in the case of accurate rotational data not always fully quantitative reproduction.