Pulsed Co2-Laser Excitation of 03/02 Mixtures at Pressures From 0.16 to 1.20 Bar

Abstract

An investigation is presented of the transient vibrational excitation of O3 in the collision dominated regime initiated by pulsed CO2-laser radiation. IR-UV-double resonance experiments and measurements of the absorbance for the CO2-laser lines 9P18, 20, and 22 were carried out. Mixtures of O3 (p=17 mbar) with 02 were investigated at pressures of 160 mbar ≤Pmixt≤1200 mbar and laser fluences of 0.10 J/cm2≤Fin< 2 J/cm2 . The results are interpreted by numerical simulations in terms of a comprehensive excitation/relaxation model based upon SSH-theory. Concerning the evolution of the excitation, simulated transients of the UV-absorbance compare well with the corresponding observed signals. The saturation of the absorbing O3-transitions is demonstrated by the measured fluence dependence of the absorption coefficient at the laser wavelengths. The extent of the 03-excitation can be deduced according to the model from the maximum vibrational temperature Tm reached in the v1- and v3-oscillators. Tm accessible via the UV-transients and also via the absorbed laser energy in the case of slow relaxation at 160 160​mbar≤Pmixt≤340 mbar. In this range both techniques result in the same values for Tm. The experimental and the corresponding simulated Tm depend exponentially on the laser fluence (Tm =const . F¯in0.3) provided Tm>400​K being also confirmed up to Pmixt=1200 mbar by the observed UV-transients.