Volume 118, Issue 12, 22 March 2003
Index of content:
118(2003); http://dx.doi.org/10.1063/1.1559478View Description Hide Description
The gas phase vibrational spectroscopy of a prototypical strongly hydrogen-bonded species, has been studied between 6 and 17 μm (590 and 1670 cm−1) by infrared vibrational predissociation of the ion. Infrared excitation was accomplished using the output of the free electron laser for infrared experiments (FELIX). Predissociationspectra were recorded by monitoring depletion of mass-selected ions as a function of excitation wavelength. Four prominent absorption bands are observed at 733, 890, 1048, and 1201 cm−1. They are assigned to the fundamental of the hydrogenic stretching mode and a sequence of combinations Additional features to the blue of these bands spaced by ∼21 cm−1 are attributed to combination bands involving motion of the Ar messenger atom. Differences in the relative intensities of the combinations bands in comparison to previous matrix experiments are rationalized on the basis of the underlying dissociation dynamics.
Three-dimensional orientation of single molecules observed by far- and near-field fluorescence microscopy118(2003); http://dx.doi.org/10.1063/1.1562194View Description Hide Description
We present a simple and straightforward method for determining absolute spatial orientations of transitiondipole moments of single fluorescent molecules. Far-field polarizationmicroscopy provides angles of the dipole moments projected in the plane of the sample. Optical field near total internal reflectionsurfaces has a strong component perpendicular to the sample and, for a given in-plane angle, provides unambiguous orientation of the molecular dipole moment. Experimentally, both excitation modes are alternated to monitor real-time conformational dynamics of tetramethylrhodamine molecules covalently attached to a quartz substrate.
118(2003); http://dx.doi.org/10.1063/1.1562620View Description Hide Description
Using autoregressive modeling of discrete signals, we investigate the influence of mass and size on the memory function of a tracer particle immersed in a Lennard-Jones liquid. We find that the memory function of the tracer particle scales with the inverse reduced mass of the simulated system. Increasing the particle’s mass leads rapidly to a slow exponential decay of the velocity autocorrelation function, whereas the memory function changes just its amplitude. This effect is the more pronounced the smaller and the heavier the tracer particle is.