Laser detection of nuclear spin isomers of ethylene molecules

We report the making of a double-beam laser spectrometer to measure absorption spectra in the ν₅ + ν₉ combination vibrational band of ethylene in the region of λ = 1.6 μm. The spectrometer is used to find a portion of the spectrum that has wellresolved absorption lines of all four nuclear spin isomers of ethylene molecules. The rotational quantum numbers of these absorption lines and the nuclear spin isomers of ethylene molecules responsible for them are identified.