Near Infrared Absorption of Ethylene between 5500 cm−1 and 6500 cm−1 to High Pressures and Temperatures

The near infrared absorption of pure ethylene in the region of the first overtones of the CH stretching fundamentals (5500 cm−1 to 6500 cm−1) was measured at supercritical temperatures (Tc = 9.5°C) between 22°C and 200°C from 0.05 to 3000 bar. Density and temperature dependence of bandshape, maximum frequency and absorption intensity are reported. The bands observed within a wide range of experimental conditions are assigned to combinations and overtones of vibrations. At high densities pressure induced (“forbidden”) bands occur. The molar integrated absorption intensity of the strong ν5 + ν9 combination band at 6138 cm−1 is independent of pressure and temperature. This enables spectroscopic concentration determinations on ethylene in high pressure‐high temperature equilibria and reactions.