Methane diode laser overtone spectroscopy at 840 nm

Overtone absorption lines of (CH4)-C-12 have been examined by using a tunable diode laser (TDL) spectrometer in the region around 11900 cm(-1) (840 nm) where the combination overtone band v, + 3 nu(3) lies. The spectrometer sources are commercially available heterostructure GaAlAs TDLs operating in the "free-running" mode, which allowed the detection of the line positions within 0.01 cm(-1). The wavelength modulation spectroscopy (WMS) and the second harmonic detection technique permitted the measurements of minimum absorbances of the order of similar or equal to 5 x 10(-6). This allowed to observe the weakest lines of the band with absorption cross-sections of the order of similar or equal to 2 x 10(-25) cm(2)/molecule or similar or equal to 0.5 km(-1)/amagat. For some of them self-, air-, He- and H-2-broadening coefficients have been obtained at room temperature. (c) 2006 Elsevier Ltd. All rights reserved.