March 2019

Amidogen Radical

The discovery of the triatomic amidogen radical NH2 in space was reported in 1993 by recent Kavli Prize recipient Ewine van Dishoeck and co-workers. The 110-101 transition of para-NH2 was detected in emission toward the hot cores Sgr B2(M) and Sgr B2(N) with the Caltech Submillimeter Observatory. The considerable splitting of levels due to the net doublet electron spin and nuclear spin hyperfine interactions was resolved.

Researcher Links
EF van Dishoeck
DJ Jansen
P Schilke
TG Phillips

Later confirmation of the detection of NH2 included several studies about a decade after the initial detection that didn't resolve the lines as well, including the work of Goicoechea et al. from 2004. Recently, Persson et al. performed high resolution studies of NH2 toward W31C, W49N, W51, and G34.3+0.1 with the Herschel Space Observatory that provided accurate assessments of the ortho-to-para ratio of NH2 in those sources. NH2 was also detected toward the extragalatic source PKS 1830-211 by Muller et al..

NH2 is the penultimate member of the sequence of nitrogen hydrides that begins with the imidogen radical NH and culminates with ammonia, one of the most common and ubiquitous astromolecules. Characterizing the extent to which NH2 is present in a source can help to constrain the chemistry of ammonia in that source. The animation to the left shows the sequence of building ammonia one H addition at time: N → NH → NH2 → NH3.

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