Volume 117, Issue 20, 22 November 2002
Index of content:
Cis→trans conversion of formic acid by dissipative tunneling in solid rare gases: Influence of environment on the tunneling rate117(2002); http://dx.doi.org/10.1063/1.1521429View Description Hide Description
The relaxation of the higher-energy cis conformer of formic acid to the lower-energy trans form by a tunneling mechanism has been investigated in low-temperature rare gas matrices. In the temperature range 8–60 K, the tunneling takes place dominantly from the vibrational ground state of the cis form and the temperature dependence of the tunneling rate constant is influenced by the interactions with the environment. The temperature-dependent tunneling rates for HCOOH and DCOOH in solid Ar, Kr, and Xe are measured including data for molecules in different local environments within each host. It was found that the medium and the local environment has a significant influence on the tunneling rate.
Picosecond pump–probe photoelectron spectroscopy as a probe of intramolecular dynamics in para-fluorotoluene117(2002); http://dx.doi.org/10.1063/1.1521723View Description Hide Description
Picosecond photoelectron spectroscopy is used to monitor the intramolecular dynamics in parafluorotoluene prepared with ∼1200 cm−1 of internal energy from a jet cooled sample. The spectra evolve dramatically over a 100 ps timescale supporting results from chemical timing experiments. This suggests that initial temperature has little effect on the energy redistribution rate.
117(2002); http://dx.doi.org/10.1063/1.1522399View Description Hide Description
The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about −3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length ξ and a persistence length L.