Knowledge Bank

Ethylene is a naturally occurring compound in ambient air that affects atmospheric chemistry and global climate. The C$2$H$4$ spectrum is available in databases only for the 1000 and 3000 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ ranges. In this work, {\em J. Quant. Spectrosc. Radiat. Transfer/}, {\bf 111}, 2265--2278 (2010).}, the ethylene absorption spectrum was measured in the 6030-6250 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ range with the use of a high resolution Bruker IFS 125HR Fourier-spectrometer and a two-channel opto-acoustic spectrometer with a diode laser. As a secondary standard of wavelengths, the methane absorption spectrum was used in both cases. A preliminary analysis was realized thanks to the tensorial formalism developed by the Dijon group that is implemented in the XTDS software package, {\bf 251}, 102--113 (2008).}. We considered the two combination bands $\nu 5+\nu 9$ and $\nu 5+\nu 11$ as an interacting dyad. Parameters for the $\nu 9/\nu 11$ dyad were fitted simultaneously from a re-analysis of previously recorded supersonic expansion jet FTIR data, while parameters for the $v5=1$ Raman level were taken from literature. More than 600 lines could be assigned in the 6030-6250 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region (and also 682 in the 2950--3150 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region) and effective Hamiltonian parameters were fitted, including Coriolis interaction parameters. The dyad features are globally quite well reproduced, even if there are still problems at high $J$ values.