Knowledge Bank

Six distinct pure-rotational $\Delta J=0$ transitions in $CH4\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ have been detected in emission from the Orion molecular cloud. (These transitions ate normally ``forbidden” in the vibronic ground state of tetrahedral $XY4$ molecules.) Two of these microwave lines had been reported $previously2$ The spectral frequencies in Orion A ranged from 4.6 to 82.9 GHz corresponding to J values from 11 to 20, respectively. The column density of $CH4$ in Orion A is estimated to be very large, probably second only to $H2$ which is the most abundant molecule detected there. Methane has also been observed in absorption in IRC + 10216 and RX Boo. The isotopic species $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ may have been detected in Orion A.