Study of the dependence of the photoacoustic signal amplitude from methane on different collisional partners

N. BARREIRO; A. PEURIOT; V. SLEZAK; G. SANTIAGO

VIBRATIONAL SPECTROSCOPY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 68 p. 158 - 161

0924-2031

tIn a previous work we observed that the photoacoustic signal from methane in air decreases to one-seventh the figure obtained in mixtures with pure nitrogen. A close resonance between oxygen?s firstvibrational mode () and the methane bending modes may be responsible for this phenomenon. Indeed,the long relaxation time of the mode (1554 cm−1) causes the oxygen to store energy internally insteadof releasing it to heat. In this work we study different collisional partners (Helium, C2Cl2F4) which mayhelp transfer this vibrational energy to kinetic.In order to carry out the experiment we used the resonant photoacoustic technique by means of anOPO tuned at 3.3 m, which corresponds to the methane 3vibrational mode, and an aluminum acoustic resonator with rectangular cross section, Brewster windows at the resonance nodes of the second lon-gitudinal mode at 2300 Hz and Q-factor of 165. A rate-equation-based model, which describes the timeevolution of the excited populations and the heating of the sample for the case of Helium, shows goodagreement with the experimental results. The addition of C2Cl2F4showed an increase of the methane PAsignal up to values even higher than for methane-nitrogen mixtures.