MICROWAVE OBSERVATIONS OF METHANE IN THE INTERSTELLAR MEDIUM

Six distinct pure-rotational $\\Delta J = 0$ transitions in $CH_{4}{^{1}}$ have been detected in emission from the Orion molecular cloud. (These transitions ate normally ``forbidden” in the vibronic ground state of tetrahedral $XY_{4}$ molecules.) Two of these microwave lines had been reported $previously^{2}$ 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 $CH_{4}$ in Orion A is estimated to be very large, probably second only to $H_{2}$ which is the most abundant molecule detected there. Methane has also been observed in absorption in IRC + 10216 and RX Boo. The isotopic species $^{13}CH_{4}$ may have been detected in Orion A.