The Microwave Spectrum and Structure of the Ethylene–Sulfur Dioxide Complex

The simplest π complex of SO2 with an organic molecule—C2H4 · SO2—was formed by ultrasonic expansion of a C2H4SO2Ne gas mixture. The structure derived from the microwave spectrum reveals that the SO2 and C2H4 planes are nearly parallel (Cs symmetry) and separated by 3.509 Å. The splitting pattern in the spectrum indicates the existence of a tunneling process between equivalent structures.