Time Scale Of Molecular Motions Research Articles

Dissipation, tunneling, and adiabaticity criteria for curve crossing problems in the condensed phase

The role of dissipation in curve crossing phenomena in condensed phases is discussed. Adiabaticity criteria are found in two regimes via path integral arguments. In the high temperature regime a stochastic quantum Langevin approach is developed. In the low temperature region an instanton method is used. In both cases the curve crossing time scale competes with the time scale of molecular motion. Dissipation causes the process to be more likely to be adiabatic.

Molecular motion and spin relaxation in polydiethylsiloxane

AbstractQuantitative comparison of previously published NMR spin‐relaxation data for polydiethylsiloxane with theoretical predictions for a variety of motional processes allowed both the nature and time scale of molecular motions to be identified. At the lowest temperatures, methyl reorientation produced a T1 minimum and was found to proceed with an activation energy of 2.4 kcal/mole in both amorphous and crystalline phases. Reorientation of the ethyl groups in the amorphous phase was observed at a higher temperature with an activation energy of 9.3 kcal/mole. Relaxation in the melting region was influenced by flexing and stretching of the helical polymer chain. The maximum angular displacement of the chain was estimated to be 24°, with an activation energy for this process of 2.6 kcal/mole.