Partition functions and densities of states for butane and pentane

Abstract

The thermodynamic functions S and C_p of butane and pentane are calculated and compared with the experimental data. Internal rotation and its coupling to external rotation is treated within the approximation of classical mechanics. The density of states for the combined internal and external rotation is derived from the partition function by inverse Laplace transformation and the total density of states is obtained by convolution with the vibrational density of states, calculated by direct count.