Search for methane in Comet Halley

A search for gaseous neutral CH4 was conducted in the coma of comet Halley on March 20, 1986 using a Fourier transform spectrometer on the Kuiper Airborne Observatory. In the field-of-view (24,000 km) the CH4 rotational temperature is equal to the kinetic temperature of the coma molecules due to collisions in most of the region and is frozen in at the outer edge. The spectrum of the nu3 band is due to fluorescence with the R(3) to R(5) lines being most suitable for Earth-based observations. Measured upper (3 delta) limits of 4 times 10 to the minus 19th power W/sqcm for these lines lead to a (7 delta) upper limit of 4 times 10 to the 28th power CH4 molecules per second. This value corresponds to 4% of the water vapor production rate at the time of observation.