PREPEAK IN THE STRUCTURE FACTOR OF SIMPLE MOLECULAR GLASS FORMERS

X-ray investigations of three fragile simple molecular glass forming l iquids (m-toluidine, m-cresol, methylhydrazine) are presented, in the stable, undercooled and glassy state. Upon decreasing temperature, a ' 'pre-peak'' appears in the structure factor of all the investigated co mpounds in very similar conditions. It reveals a reversible intermedia te range order of the liquid. A standard interpretation in terms of mi crocrystalline organization would lead to spatial repeat distances typ ically of 10 Angstrom and correlation length at most similar to 50 Ang strom at T-g. The features of this organization may be discussed in cr ystallographic terms from a comparison with the spectra of the crystal line varieties.