Measurement of non-radiative gas molecules relaxation rates by using quartz-enhanced photoacoustic spectroscopy

In this work, we report on the measurement of methane (CH4) effective non-radiative relaxation rate in a mixture containing 1% of CH4 and 0.15% of water vapor in nitrogen, by using a set of custom quartz tuning forks (QTFs). The dependence of quartz-enhanced photoacoustic spectroscopy (QEPAS) peak signal and QTF quality factor as a function of operating pressure allowed the estimation of the radiation-to-sound conversion efficiency and, consequently, the calculation of the effective relaxation rate of the investigated gas mixture. We measured an effective relaxation rate of 3.2 ms·Torr, in good agreement with values reported in literature.