Temperature dependent Raman measurements on insulating ${\mathrm{YH}}_{3-\delta }$ thin films are reported. With increasing temperature we observe a huge broadening of a line corresponding to an yttrium mode. This particular mode is assigned to a breathing vibration of the yttrium atoms around an octahedral hydrogen position. The line broadening is discussed in terms of a coupling between this breathing mode and the electron excited from an octahedral H vacancy into the $4d$ conduction band of Y, corroborating the strong correlation models for the electronic structure of ${\mathrm{YH}}_3$.

• Received 8 July 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.017401