PRESSURE-INDUCED DYNAMICS IN SOLID N-ALKANES AS PROBED BY OPTICAL SPECTROSCOPY

The dependence of frequency, width, and area of spectral holes on pres sure were measured at 1.6 K in the pressure range up to 2.5 MPa for di methyl-s-tetrazine (DMST) doped n-hexane (Shpol'skii system), and as r eference systems, for DMST-doped durene (''hard'' molecular crystal) a nd ethanol:methanol glass. For the Shpol'skii system, in addition the inhomogenous fluorescence spectra were measured for normal and high (2 00 MPa) pressures. The main observations were the following: (i) spect ral holes in the Shpol'skii system exhibit very large pressure-induced broadening (up to 65 GHz/MPa) depending essentially on the prehistory (freezing pressure) and exceeding the corresponding values for durene (by far) and glass; (ii) spectral holes in the Shpol'skii system exhi bit strong, and to a large extent, reversible, area reduction with app lied pressure; and (iii) the inhomogeneous fluorescence lines show qui te a moderate (as compared to holes) pressure broadening of about seve ral GHz/MPa. The results for the Shpol'skii system are shown to be inc onsistent with existing theories. They are qualitatively explained by pressure-induced dynamics of vacancy defects in the frozen n-alkanes. (C) 1998 American Institute of Physics.