Molecular dynamics of CH2Cl2: temperature dependences of the far infra-red spectrum. Part 1: experimental and simulation

The temperature dependence of the rotational diffusion in liquid CH2Cl2 has been measured in the far infrared from 10 to 220 cm−1 and 177K to 313K (f.p. to b.p. at 1bar). The results are interpreted at 177K and 293K with a molecular dynamics simulation using a 5 × 5 atom-atom potential with charge-charge electrodynamics. The simulation reproduces the basic features of the spectra but some experimental detail of the dependency of f_max,the far infrared peak frequency,on temperature is not followed by the simulation. The situation can be improved by accurately measuring the second dielectric virial coefficient βϵ of CH2Cl2 vapour in order to improve our knowledge of the intermolecular pair potential.