January 2015

Methyl Radical

The methyl radical (CH3) was detected toward Sgr A* (the galactic center) by Feuchtgruber et al. in 2000 with the Infrared Space Observatory (ISO). Unlike most observed interstellar astromolecules, the methyl radical has no dipole moment and thus can't be detected with pure rotational spectroscopy. However, two of the distinctive rovibrational features of CH3 were observed. Knez et al. reported confirming evidence of CH3 toward NGC 7538 IRS 1 in 2009.

Contrary to VSEPR theory logic, the methyl radical is planar. The images below depict the ν2 vibrational mode that gives rise to the observed features (left), the bonding diagram for CH3 showing the singly occupied 2p orbital on C (center), and an isodensity surface for that orbital (right).

vibrational
mode
bonding
diagram
singly occupied
orbital

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