Determination of the relaxation time of the 103 H2O vibration with an optoacoustic spectrometer and a ruby laser

A method was developed for the determination of the vibrational-translational (VT) relaxation time of gases, based on the dependence of the sensitivity of an optoacoustic detector on the pressure of the investigated gas in a cell under pulse excitation conditions. An optoacoustic spectrometer and a pulsed ruby laser were used to determine the relaxation time of the 103 vibration in H₂O vapor. The value obtained, τ_VT(103) = (2.1±0.4)×10^–7 sec·atm, was in qualitative agreement with the results of an experimental determination of the VT relaxation time of the lower H₂O vibration modes (010, 100, 001, 020).