Picosecond spectroscopy of vibrational and electronic dynamics in high-pressure molecular solids

Picosecond time resolved studies of vibrational and electronic dynamics in molecular solids are presented. In the first, several uranyl compounds were selected that had large gaps in their vibrational energy density of states. Picosecond coherent anti-Stokes Raman measurements (psCARS) revealed that at 10 K vibrational relaxation occurs by at least a fifth order anharmonic mechanism. However, at elevated temperatures vibrational decay is found to proceed predominantly by a cubic anharmonic upconversion mechanism.; In a second study the results of some of the first psCARS on a low temperature molecular solid in a high pressure diamond anvil cell are presented. For carbon disulfide pressure induced shifts in the phonon frequencies result in the opening up of a new relaxation pathway for the {dollar}2nusb2{dollar} mode. This pressure induced relaxation mechanism appears to dominate the dynamics of this mode at pressures greater than 19 kbar.; In the third project pressure dependent low temperature psCARS measurements for the {dollar}nusb9,{dollar} {dollar}nusb8,{dollar} and {dollar}nusb5{dollar} of naphthalene are presented. Pressure induced density of states effects are isolated, thereby allowing the first direct observations of pressure induced anharmonic coupling effects. The results indicate that the magnitude of the pressure induced anharmonic coupling is highly mode specific.; In a fourth study psCARS measurements at low temperature are performed on homogeneous high pressure crystals and on highly strained crystals. Results are analyzed in terms of competition between vibrational relaxation and inhomogeneous dephasing. Changes in vibrational dephasing induced by a large negative pressure change ({dollar}-Delta{dollar}P {dollar}ge{dollar} 5 kbar) are used to determine the magnitude of inhomogeneous dephasing effects. The strain induced inhomogeneous dephasing is found to be mode specific.; Finally the first picosecond photon echo measurements on a molecular solid in a high pressure diamond anvil cell at low temperature are presented. Results for the O{dollar}sb1{dollar} and O{dollar}sb3{dollar} photosites in pentacene doped p-terphenyl are presented. The results are discussed in terms of pressure induced changes in the Debye frequency.