Criegee intermediate

A Criegee intermediate (also called a Criegee zwitterion or Criegee biradical) is a carbonyl oxide with two charge centers. These molecules help to break down sulfur dioxide and nitrogen dioxide in the atmosphere, and may help offset global warming.

The formation of this sort of structure was first postulated in the 1950s by Rudolf Criegee, for whom it is named, but it wasn't until 2013 that direct detection of such chemicals was reported. Infrared spectroscopy suggests the electronic structure is a zwitterion rather than a biradical as some had proposed.