February 2019

Methylene Radical

Six years after reporting a tentative detection of the methylene radical (CH2) in 1989, the team of Hollis, Jewell, and Lovas confirmed the detection in 1995. As the authors note, detecting CH2 is challenging due to a number of factors: only one rotational transition falls within the window where ground-based telscopes can search, and this transition is spread into weaker fine structure lines. Both sets of observations were made with the NRAO 12m telescope. The receiver was upgraded between 1989 and 1995, making better observations possible.

Researcher Links
JM Hollis
PR Jewell
FJ Lovas

Although it resembles the water molecule—both are v-shaped and thus polar—the bonding in CH2 is not the straightforward pair of σ bonds found in water. The ground state of CH2 is an open-shell triplet with one of the unpaired electrons in an in-plane orbital and one in a out-of-plane orbital. This occurs because of recoupled pair bonding.

As shown to the right, CH2 was also the subject of early (1944) research by D. Duck (as reported by Gaspar & Hammond in "The Spin States of Carbenes").

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