UC Riverside

The parameters of temperature and, particularly, pressure are useful tools for the investigation of the phase transitions and vibrational dynamics of condensed matter, such as molecular crystals. Building upon the design of the Merril-Bassett Diamond Anvil Cell (DAC), a Dynamic DAC was developed and shown to be able to dynamically control the pressure of the sample. Also, the dynamic phase changes of water to solid Ice VI and VII were imaged using the Dynamic DAC.

Using a standard DAC, the hydrogen bonding of both N1,N1,N5,N5,3,3- hexamethylcadaverine HBr (33HMCHBr) and N,N,N',N'-tetramethylputrescine HI (TMPHI) were explored using high pressure Raman spectroscopy. Evidence of a possible phase transition for 33HMCHBr is shown along with the likely vibrational mode of the low barrier hydrogen bond in TMPHI.

New single crystal x-ray crystallographic evidence is shown regarding a new crystal structure of p-terphenyl involving twinning at low temperature as well as x-ray diffraction evidence of the temperature induced phase transition in p-terphenyl.

Lastly, the results of computational studies, using a previously developed forcefield, of the pentacene in p-terphenyl mixed molecular crystal are shown. The polarizations of the calculated modes of the hindered translations of pentacene along the molecular and crystallographic axes and the anharmonicity of the modes are investigated. Also, a discussion on the identification and separation of the intramolecular motions from the calculated hindered rotations spectrum is presented.