261 research outputs found
Long-range interactions in the ozone molecule: spectroscopic and dynamical points of view
Using the multipolar expansion of the electrostatic energy, we have
characterized the asymptotic interactions between an oxygen atom O and
an oxygen molecule O, both in their electronic ground state.
We have calculated the interaction energy induced by the permanent electric
quadrupoles of O and O and the van der Waals energy. On one hand we
determined the 27 electronic potential energy surfaces including spin-orbit
connected to the O + O dissociation limit of the
O--O complex. On the other hand we computed the potential energy curves
characterizing the interaction between O and a O
molecule in its lowest vibrational level and in a low rotational level. Such
curves are found adiabatic to a good approximation, namely they are only weakly
coupled to each other. These results represent a first step for modeling the
spectroscopy of ozone bound levels close to the dissociation limit, as well as
the low energy collisions between O and O thus complementing the knowledge
relevant for the ozone formation mechanism.Comment: Submitted to J. Chem. Phys. after revisio
Progress in strain monitoring of tapestries
This paper reports interdisciplinary
research between conservators and
engineers designed to enhance the
long-term conservation of tapestries
(tapestry-weave hangings) on longterm
display. The aim is to monitor,
measure and document the strain
experienced by different areas of a
tapestry while it is hanging on display.
Initial research has established that
damage can be identified in the early
stages of its inception, i.e., before it is
visible to the naked eye. The paper also
reports initial results of strain data
visualisation that allows curators and
conservators to examine how strain
develops, thereby facilitating
predictions about the changes in the
form or condition of the tapestry.
Strain data visualisation also allows the
strain process to be recorded, thereby
facilitating the effective documentation
of display methods and conservation
interventions. The paper reports the
use of point measurements (using
silica optical fibre sensors) and full-field
monitoring (using 3-D
photogrammetry with digital image
correlation (DIC))
Long term condition monitoring of tapestries using image correlation
Digital Image Correlation (DIC) is used to extract non-contact full-field three-dimensional displacement and in-plane strains from an historic tapestries. A DIC-based approach is devised that allows the effect of RH variations on a tapestry to be quantified. A historical tapestry has been monitored in a closely controlled environment and in the natural environment. The results revealed that very small variations in RH can have significant effects on strain. An automated long term monitoring approach has been devised to allow strain data to be extracted in real time from tapestries in remote locations. The results show that DIC provides better understanding of the effect of RH fluctuations on strain which will ultimately lead to more insight into the degradation process of historical tapestries. The paper demonstrates the potential for using DIC as a condition monitoring tool
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
Triplet-singlet conversion in ultracold Cs and production of ground state molecules
We propose a process to convert ultracold metastable Cs molecules in
their lowest triplet state into (singlet) ground state molecules in their
lowest vibrational levels. Molecules are first pumped into an excited triplet
state, and the triplet-singlet conversion is facilitated by a two-step
spontaneous decay through the coupled
states. Using spectroscopic data and accurate quantum chemistry calculations
for Cs potential curves and transition dipole moments, we show that this
process has a high rate and competes favorably with the single-photon decay
back to the lowest triplet state. In addition, we demonstrate that this
conversion process represents a loss channel for vibrational cooling of
metastable triplet molecules, preventing an efficient optical pumping cycle
down to low vibrational levels
Strain monitoring of tapestries: results of a three-year research project
The outcomes of an interdisciplinary research project between conservators and engineers investigating the strain experienced by different areas of a tapestry are described. Two techniques were used: full-field monitoring using digital image correlation (DIC) and point measurements using optical fibre sensors. Results showed that it is possible to quantify the global strain across a discrete area of a tapestry using DIC; optical fibre and other sensors were used to validate the DIC. Strain maps created by the DIC depict areas of high and low strain and can be overlaid on images of the tapestry, creating a useful visual tool for conservators, custodians and the general public. DIC identifies areas of high strain not obvious to the naked eye. The equipment can be used in situ in a historic house. In addition the work demonstrated the close relationship between relative humidity and strain
Photoassociation of a cold atom-molecule pair: long-range quadrupole-quadrupole interactions
The general formalism of the multipolar expansion of electrostatic
interactions is applied to the calculation the potential energy between an
excited atom (without fine structure) and a ground state diatomic molecule at
large separations. Both partners exhibit a permanent quadrupole moment, so that
their mutual quadrupole-quadrupole long-range interaction is attractive enough
to bind trimers. Numerical results are given for an excited Cs(6P) atom and a
ground state Cs2 molecule. The prospects for achieving photoassociation of a
cold atom/dimer pair is thus discussed and found promising. The formalism can
be easily generalized to the long-range interaction between molecules to
investigate the formation of cold tetramers.Comment: 5 figure
Saturation of Cs2 Photoassociation in an Optical Dipole Trap
We present studies of strong coupling in single-photon photoassociation of
cesium dimers using an optical dipole trap. A thermodynamic model of the trap
depletion dynamics is employed to extract absolute rate coefficents. From the
dependence of the rate coefficient on the photoassociation laser intensity, we
observe saturation of the photoassociation scattering probability at the
unitarity limit in quantitative agreement with the theoretical model by Bohn
and Julienne [Phys. Rev. A, 60, 414 (1999)]. Also the corresponding power
broadening of the resonance width is measured. We could not observe an
intensity dependent light shift in contrast to findings for lithium and
rubidium, which is attributed to the absence of a p or d-wave shape resonance
in cesium
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