Determination of the VT-relaxation time of molecules from the compression pulse width of a photoacoustic signal: the effect of gas pressure measurement errors
A.E. Protasevich, B.A. Tikhomirov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, 1, Academician Zuev square, Tomsk, 634021, Russia
Keywords: оптико-акустический метод, колебательно-поступательная релаксация молекул, ошибка восстановления, photoacoustic method, vibration-translational (VT) relaxation of molecules, error of restoration
Abstract
The influence of gas pressure measurement errors in the chamber of a photoacoustic detector on accuracy of restoration of fast VT-relaxation time of molecules is investigated with the use of numerical simulation of a shape of photoacoustic signal. Using the relaxation of water vapor molecules from the lower excited vibrational state as an example, it is found that for values of the radius of the Gaussian laser beam ω0 ~ 1 mm, typical in experiments with MK-301 microphone, the relaxation time τ0VT ~ 10-6 s x mbar can be restored from the dependencies of duration of photoacoustic compression pulse on gas pressure with a relative errors δτ0VT ≤ 10%, if systematic measurement error of pressure does not exceed 0.03 mbar. An error of restoration is directly proportional to the propagation time of sound through the illuminated area.
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