99 research outputs found
Theory of Bose-Einstein condensation for trapped atoms
We outline the general features of the conventional mean-field theory for the
description of Bose-Einstein condensates at near zero temperatures. This
approach, based on a phenomenological model, appears to give excellent
agreement with experimental data. We argue, however, that such an approach is
not rigorous and cannot contain the full effect of collisional dynamics due to
the presence of the mean-field. We thus discuss an alternative microscopic
approach and explain, within our new formalism, the physical origin of these
effects. Furthermore, we discuss the potential formulation of a consistent
finite-temperature mean-field theory, which we claim necessiates an analysis
beyond the conventional treatment.Comment: 12 pages. To appear in Phil. Trans. R. Soc. Lond. A 355 (1997
Absolute frequency measurements of 85Rb nF7/2 Rydberg states using purely optical detection
A three-step laser excitation scheme is used to make absolute frequency
measurements of highly excited nF7/2 Rydberg states in 85Rb for principal
quantum numbers n=33-100. This work demonstrates the first absolute frequency
measurements of rubidium Rydberg levels using a purely optical detection
scheme. The Rydberg states are excited in a heated Rb vapour cell and Doppler
free signals are detected via purely optical means. All of the frequency
measurements are made using a wavemeter which is calibrated against a GPS
disciplined self-referenced optical frequency comb. We find that the measured
levels have a very high frequency stability, and are especially robust to
electric fields. The apparatus has allowed measurements of the states to an
accuracy of 8.0MHz. The new measurements are analysed by extracting the
modified Rydberg-Ritz series parameters.Comment: 12 pages, 5 figures, submitted to New. J. Phy
A theoretical study of the 1B2u and 1B1u vibronic bands in benzene
The two lowest bands, 1B2u and 1B1u, of the electronic spectrum of the benzene molecule have been studied theoretically using a new method to compute vibronic excitation energies and intensities. The complete active space (CAS) self-contained field (SCF) method (with six active π-orbitals) was used to compute harmonic force field for the ground state and the 1B2u and 1B1u electronic states. A linear approximation has been used for the transition dipole as a function of the nuclear displacement coordinates. Derivatives of the transition dipole were computed using a variant of the CASSCF state interaction method. Multiconfigurational second-order perturbation theory (CASPT2) was used to obtain absolute excitation energies (12 active π-orbitals). The results show that the approach works well. Vibrational progressions are well described in both bands and intensities, and energies are in agreement with experiment, in particular when CASPT2 derived geometries are used. One interesting result is that computed vertical energies fall about 0.1 eV on the high energy side of the band [email protected]
Non-Born-Oppenheimer calculations of the lowest vibrational energy of HD including relativistic corrections
In this work we report variational calculations of the two lowest vibrational states of the HD molecule within
the framework that does not assume the Born-Oppenheimer BO approximation. The nonrelativistic energies
of the states were corrected for the relativistic effects of the order of 2 where = 1
c , calculated as expectation
values of the operators representing these effects with the nonrelativistic non-BO wave functions. The non-BO
wave functions were expanded in terms of the one-center explicitly correlated Gaussian functions multiplied by
even powers of the internuclear distance. The v=0→1 transition energy obtained in the calculations is compared
with the previous calculations, as well as with the transition frequency obtained from the experimental
spectra. The comparison shows the need to include corrections higher than second order in to further
improve the agreement between the theory and the experimen
Stimulated Raman emission and absorption
Since the first observations of stimulated Raman
scattering in 1962, the outstanding problems have been concerned with explanations of the observed gain, line width and directional properties of the emitted radiation. Significant discrepancies between experiment and theory have been found, including for example measurements of gain as high as 100 times that expected, line widths as large as 500 cm-1 and angles of emission 50 percent larger than predicted. Recently these difficulties have been somewhat clarified with the discovery of selffocusing of the laser beam during the generation of stimulated Raman radiation and with the identification of two independent classes of stimulated Raman radiation with different spectral and directional properties.The present paper is concerned with measurements of (1) the frequencies and line widths of pure liquids and mixtures, and (2) the directional characteristics of anti-Stokes and Stokes emission in liquids and solids.It is found that with л single-mode » excitation there are slight frequency shifts (~ 1 cm-1) and small broadening (~ 5 cm-1), and in some cases narrowing, of spectral lines with varying concentrations in mixtures. However, with « multiple-mode » excitation the measured shifts and broadening are one or two orders of magnitude larger. The direction of anti-Stokes emission in diamond has been measured and found to be in agreement with theory, just as in calcite, the only other solid whose directional dependence has been studied. Further measurements of the emission angles in benzene, toluene and nitrobenzene under various experimental conditions, however, do not agree with either the simple momentum conservation relation or with present theories which include the effects of the « active region »
Raman Spectra of Hydrogen, Deuterium, and Nitrogen Obtained with a 21 ft. grating
Author Institution: National Research Council (Canada)Presentations without an abstract printed in the proceedings do not have an abstract (image or text) in the Knowledge Bank record
Rotational Raman Spectrum of Benzene
Author Institution: National Research Council (Canada)Presentations without an abstract printed in the proceedings do not have an abstract (image or text) in the Knowledge Bank record
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