High-resolution Spectra of Bromo Methane and Methyl Bromide Obtained by a Continuously Tunable 10-bar CO₂ Laser Based Photoacoustic Spectrometer

Abstract

High resolution spectral data of 100 ppmV ( 10⁻⁶ per volume) concentrations of the trace gases bromo methane (BM, CH₃Br), and methyl bromide (DME, (CH₃)₂O), buffered in synthetic air (80% N₂, 20% 0₂) at atmospheric pressure and room temperature are reported. The spectra are recorded with a continuously tunable 10-bar CO₂ laser based photoacoustic (PA) spectrometer. The tuning range covers 76 cm^-1 between 9.2 pm (1087 cm^-1) and 10.7 pm (935 cm^-1) at a constant narrow line-width of 0.018 cm^-1 (540 MHz). The non-resonant PA measuring cell employs an in-line 10-microphonc array. The estimated detection limits for BM and DME are approximately 2 ppmV for a signal-to-noise ratio (SNR) of 3. This corresponds to a calculated detection limit of ~76 ppbV for ethylene.