Selectivity Enhancement in Photoacoustic Gas Analysis via Phase-sensitive Detection at High Modulation Frequency
This invention is a new spectroscopic method of distinguishing molecular species with overlapping absorption spectra. Spectroscopic distinguishing between two species having overlapped optical absorption spectra is difficult and at times impossible. However, photoacoustic spectroscopy (PAS) allows the measurement of another physical property of a molecule in a gas mixture, namely its relaxation rate. This is the V T transfer rate if the molecular vibration is optically excited, or it can be the energy transfer from other internal degrees of freedom such as electronic excitation to translational motion.
Advantages Compared to the traditional way of performing PAS when the optical modulation period is much longer than the relaxation rate, the proposed approach allows the separation different chemical species based on their relaxation rate difference, even if their optical spectra are strongly overlapping.
Potential Applications The invention is to be used to spectroscopically detect and quantify concentrations of a chemical species in the presence of another species with an overlapping absorption spectrum. An example of an industrial application is CO trace concentrations measurements in propylene required in the manufacture of plastics by the petro-chemical industry.
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