Far-infrared and computer-simulation analysis of liquid and rotator-phase bromoform

Abstract

The existence of a liquid-to-rotator phase transition in bromoform is confirmed by far-infrared interferometric and laser spectroscopy. The molecular dynamics of liquid bromoform a few degrees above the melting point are simulated by computer and a variety of spectral data produced for comparison with experimental indications. It is easier to reproduce “single-molecule” infrared, Raman and n.m.r. correlation times than those from “multi-molecule” sources such as dielectric, far-infrared and Rayleigh-scattering spectroscopy. The computer simulation shows that roatation is nearly completely decoupled from translation in liquid and rotator-phase bromoform a few degrees above and below the phase transition, respectively. There is strikingly less rotation–translation coupling than in CH₃CN for example, a more elongated and dipolar molecule with the same C_3ν symmetry which does not form a rotator phase.