Investigating the rigidity of ortho-terphenyl

The molecular glass former ortho-terphenyl has traditionally been used as a model system for rigid molecular solids. This assumption has been questioned, and therefore its rigidity was investigated by experimental terahertz time-domain spectroscopy and low-frequency Raman spectroscopy and theoretical density functional theory. The results show that there are a number of coupled internal and external motions present in the terahertz regime that contradict the assumption that orthoterphenyl is rigid.