Diode laser overtone spectroscopy of methane at 780 nm
Abstract
A tunable diode laser spectrometer has been employed to examine the overtone absorption lines of 12CH4 in the region around 12780 cm-1 (780 nm) at room temperature. The spectrometer sources are commercially available tunable diode lasers operating in "free-running" mode. The measurement of the line positions within 0.01 cm-1 has been possible by the use of the wavelength modulation spectroscopy and the second harmonic detection techniques that permitted the observation of minimum optical absorbances of the order of ≈ 10-6. The weakest observed lines of the band have absorption cross sections of the order of 1 × 10-25 cm2/molecule, that is 0.3 km-1/amagat. For some of them self-, air-, He- and H2-broadening coefficients have been obtained.
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