MEASUREMENT OF ROTATIONAL AND VIBRATIONAL-RELAXATION IN GASES BY PHOTOACOUSTIC RESONANCE - APPLICATION TO SF6

The photoacoustic resonance method has been applied to study molecular relaxation in a cylindrical cavity. The profile of the acoustic reson ance, excited by the vibrational mode upsilon(3) of gas sample SF6 wit h a CO6 laser, was measured as a function of pressure between 1 and 80 0 Torr. A general theoretical treatment of vibrational and rotational relaxation on the acoustically resonant characteristics, such as the r esonant frequency and the broadening of half-width taking into account the contributions of surface and volume losses, and the nonideality o f gas, was worked out in detail and was used io frame the discussion o f the relaxation processes following the vibrational excitation. The a nalysis of the experimental data yields a value of vibrational relaxat ion time (p tau)(V-T) = 0.21 +/- 0.01 mu s atm, and a value of (p tau) (R-T) = 0.09 +/- 0.06 ns atm for the rotational relaxation time of SF6 at T = 295 K. (C) 1996 American Institute of Physics.