Diode laser spectroscopy of methane overtone transitions

With the aid of commercial room-temperature AlGaAs diode lasers, frequency modulation absorption spectroscopy was performed on the 7900 Å and 8600 Å ro-vibrational combination overtone bands of methane. Three weak transitions are reported in the range around 8610 angstrom 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 Å) were derived from CH4 and for CH4 immersed in N2 and He buffer gases. An evaluation of the methane detection sensitivity is given for favorable laboratory conditions as well as for an open-path situation.