Index of content:
Volume 122, Issue 6, 08 February 2005
122(2005); http://dx.doi.org/10.1063/1.1857472View Description Hide Description
We report quantum diffusion Monte Carlo (DMC) and variational calculations in full dimensionality for selected vibrational states of using a new ab initiopotential energy surface [X. Huang, B. Braams, and J. M. Bowman, J. Chem. Phys.122, 044308 (2005)]. The energy and properties of the zero-point state are focused on in the rigorous DMC calculations. OH-stretch fundamentals are also calculated using “fixed-node” DMC calculations and variationally using two versions of the code MULTIMODE. These results are compared with infrared multiphoton dissociation measurements of Yeh et al. [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys.91, 7319 (1989)]. Some preliminary results for the energies of several modes of the shared hydrogen are also reported.
Emergence of a new feature in the high pressure–high temperature relaxation spectrum of tri-propylene glycol122(2005); http://dx.doi.org/10.1063/1.1858857View Description Hide Description
We investigated dielectric relaxation of a tri-propylene glycol system under high compression. By increasing temperature and pressure we observed that a new relaxation process emerges from the low frequency tail of the structural peak. This new peak starts to be visible at about 0.5 GPa and becomes clearly evident at 1.7 GPa. However, this additional peak merges again with the structural one as the glass transition is approached, since it has a weaker temperature dependence. This finding enriches the relaxation scenario of molecular glass formers confirming that the application of very high hydrostatic pressure can favor the detection of new relaxation or otherwise unresolved processes in supercooled liquid systems.
Using fluorescence resonance energy transfer to measure distances along individual DNA molecules: Corrections due to nonideal transfer122(2005); http://dx.doi.org/10.1063/1.1854120View Description Hide Description
Single molecule fluorescence resonance energy transfer has been extensively used to measure distance changes and kinetics in various biomolecular systems. However, due to complications involving multiple de-excitation pathways of the dyes, the absolute inter-dye distance information has seldom been recovered. To circumvent this we directly probe the relative variations in the quantum yield of individual fluorophores. B-DNA was used as a scaffold to position the donor (Cy3 or TMR) at precise distances from the acceptor (Cy5) within the Förster radius. We found that the variation in the Cy3 quantum yield is times larger than that of TMR. By taking into account the molecule-to-molecule variability in the acceptor/donor quantum yield ratio, the apparent fluorescence resonance energy transfer efficiencies were scaled to yield the theoretical values. We obtained very good agreement with a physical model that predicts distances along B-DNA.