Infrared and Raman spectra of BrF5 and ClF3 in the condensed phase. Evidence of an associated state in liquid ClF3

Raman laser spectra of BrF5 and ClF3 have been investigated between 13 and 293 K. Infrared spectra were recorded and analyzed at liquid nitrogen temperature. Vibrational spectra of solid BrF5 agree with the crystallographic data and display the splitting of all transitions into two components, except for ν1, which is only shifted. A type of intermolecular interaction is considered, which accounts for the Raman spectrum. The vibrational study of ClF3 has shown an associated state in the liquid and a solid−solid transition at 192.6 K with an intermediate phase covering 5 K. A dynamical model for association is set up to explain both NMR and Raman spectra. The associated species in the liquid are intimately connected with the structure of the intermediate phase; moreover, the splittings of transitions into doublets allow one to expect molecular interactions similar to those in BrF5.