DIODE-LASER SPECTROSCOPY OF METHANE OVERTONE TRANSITIONS

With the aid of commercial room-temperature AlGaAs diode lasers, frequ ency modulation absorption spectroscopy was performed on the 7900 angs trom and 8600 angstrom rovibrational combination overtone bands of met hane. Three weak transitions are reported in the range around 8610 ang strom that, to our knowledge, have not yet been observed and measured. Self-broadening and pressure-broadening coefficients of one of these new absorption features (at 8608.93 angstrom) were derived from CH4 an d for CH4 immersed in N2 and He buffer gases. An evaluation of the met hane detection sensitivity is given for favorable laboratory condition s as well as for an open-path situation.