Study of collisional relaxation of acetylene with spherical photoacoustic cell

With a spherical cell, photoacoustic resonance experiments have been perfor med for C2H2. The first radial mode of the spherical cell was excited using the chopped beam of a Ti:sapphire laser. High Q value of 590 has been achi eved for C2H2 gas at the pressure of 50 Torr. The resonant peak broadening is mainly due to the vibrational-translational relaxation of C2H2. An expre ssion for acoustic amplitude as a function of modulation frequency, relaxat ion time. and other parameters has been derived. This theoretical formula w as fitted to the experimental data. and the relaxation time was then determ ined. Our work reveals a double relaxation process for C2H2.