For smaller molecules like ethene, the webbook by NIST is a good source of experimental data. Search results for ethene in particular here yield both a figure of a vacuum UV spectrum, indicating an absorption maximum centred around 160-165 nm with $\log \epsilon$ of about 4.2, as well with a primary literature reference (Platt, J.R.; Price, W.C., J. Chem. Phys., 1949, 17, 466).
Of course, other databases like Scifinder/Chemical Abstracts by the American Chemical Society may indidicate more recent data. A specialized compilation, more suitable for ethene in particular, is the MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest here, with an entry about ethene.
Side note: NIST database equally offers access to other thermophysical data (like Vibrational and/or electronic energy levels) potentially of interest for you, too.
Addendum: With the searchable Computational Chemistry Comparison and Benchmark DataBase, NIST equally hosts numerous results of calculations of energies and structures for small molecules. This that may serve as a valuable reference, comparing the methods with each other, as well against experimentally determined data.