High-resolution synchrotron far-infrared spectroscopy of acrolein: The vibrational levels below 700 cm−1

The far-infrared spectrum of acrolein, CH2CHCHO, is studied in the 100-360 cm−1 region using continuum radiation from a synchrotron source. The combination of a very high resolution spectrometer, a long absorption path, and a low sample pressure, yields observed line widths of less than 0.0008 cm−1. Observation of the ν18 (157.9 cm−1), and ν13 (323.8 cm−1) fundamental bands, together with six hot bands in the same regions, gives information on eight low-lying vibrational states of the molecule, including the Fermi and Coriolis interactions among them. Combining the present assignments with previous data on the ν12 (564.34 cm−1) and ν17 (593.08 cm−1) fundamental bands, all ten excited vibrational levels below 700 cm−1 are analyzed in terms of one 1-state fit, two 2-state fits, and one 5-state fit.