PHASE AND PHASE-CHANGES IN CLUSTERS OF TERT-BUTYL THIOL

Clusters of tert-butyl thiol (TBT) were generated by condensation of v apor in supersonic flow under various expansion conditions, and their structures were examined during their free flight by electron diffract ion. The system had been selected because of its similarity to tert-bu tyl chloride (TBC), a much more thoroughly studied material with an in teresting solid-state chemistry. The warmest crystalline phase of TBT observed fcr the clusters (diameter, approximate to 130 Angstrom) was the known high-temperature cubic phase I with a lattice constant of 8. 609(5) Angstrom at approximate to 160 K. A second phase into which pha se I nucleated at a rate of approximate to 10(28) m(-3) s(-1) at about 157 K was also observed, as well as a third phase generated under con ditions of very cold flow. All of the phases gave the rapidly damped, diffuse diffraction patterns characteristic of submicroscopic-poorly o rdered, plastically crystalline materials. Patterns were far less dist inct than those of TBC, and the structures of the colder two phases co uld not be determined. From the rapid nucleation rate of phase I into the second phase, it could be inferred that a major translational rear rangement of the molecules could not have been involved. (C) 1997 Else vier Science B.V.