High resolution spectroscopy and a theoretical line list of ethylene between 5000 and 9000 cm-1

The absorption spectrum of ethylene (C2H4) in the range 5000-9000 cm-1 has been recorded by high-resolution Fourier transform spectroscopy (FTS) at four temperatures (130, 201, 240 and 297 K) and two pressures for each temperature value. The recorded spectra show a very high spectral congestion even at the lowest temperature. Here we present the analysis of a subset of the data limited to a weak absorption interval (6700-7260 cm-1) at 130 and 297 K. An empirical list of 12,243 lines was retrieved from the 130 K spectrum. Line intensities range between about 10-25 and 10-22 cm/molecule. In the 7120-7260 cm-1 region, a list of 2276 lines was combined to the 130 K list to derive the empirical value of the lower state energy of 1249 transitions from the variation of the line intensity between 130 and 297 K (2T-method). The line list of 12C2H4 transitions calculated by the variational method is provided in the 5200-9000 cm-1 range (241,921 and 179,927 transitions at 296 K and 130 K, respectively, above an intensity cutoff of 1x10-25 cm/molecule). This list is an extension of the Theoretical Reims-Tomsk Spectral (TheoReTS) list available at lower energy. In spite of the considerable spectral congestion and of significant deviations between the variational and experimental line lists, 647 transitions could be rovibrationally assigned to seven vibrational bands in the FTS spectrum at 130 K between 6700 and 7260 cm-1. The assignments rely on the position and intensity agreement combined with a systematic use of Lower State Combination Difference (LSCD) relations. The comparison between the empirical values of the lower state energy and their exact value provided by the rovibrational assignment is discussed.