The photoacoustic resonance method has been applied to study molecular relaxation in a cylindrical cavity. The profile of the acoustic resonance, excited by the vibrational mode &ugr;3of gas sample SF6with a CO2laser, was measured as a function of pressure between 1 and 800 Torr. A general theoretical treatment of vibrational and rotational relaxation on the acoustically resonant characteristics, such as the resonant frequency and the broadening of half‐width, taking into account the contributions of surface and volume losses, and the nonideality of gas, was worked out in detail and was used to frame the discussion of the relaxation processes following the vibrational excitation. The analysis of the experimental data yields a value of vibrational relaxation time (p&tgr;)V‐T=0.21±0.01 &mgr;s atm, and a value of (p&tgr;)R‐T=0.09±0.06 ns atm for the rotational relaxation time of SF6atT=295 K. ©1996 American Institute of Physics.