Vibrational-rotational-translational energy exchange in some polyatomic molecules

Abstract

An investigation of vibrational-translational and rotational-translational energy transfer in n-butane, n-pentane, n-hexane, cyclopentane and neopentane through ultrasonic dispersion and absorption measurements at 298.2°K and in the frequency/pressure range 10 to 5000 Mc/sec atm is reported. The measured vibrational relaxation times are for n-butane, 1.30 × 10^–9sec atm, for n-pentane, 1.14 × 10^–9sec atm, for n-hexane, 1.23 × 10^–9sec atm, for cyclopentane, 1.93 × 10^–9sec atm and for neopentane, 4.35 × 10^–9sec atm. The results for the normal paraffins are consistent with the assumption that rotational equilibrium is achieved as efficiently as translational equilibrium, but for cyclopentane the rotational collision number is 2.4 collisions and for neopentane 3.7 collisions. These results are discussed in the light of simple classical and quantum-mechanical theories of molecular energy transfer.