The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
W. Ubachs - One of the best experts on this subject based on the ideXlab platform.
-
relativistic and qed effects in the Fundamental Vibration of t2
Physical Review Letters, 2018Co-Authors: Madhu T Trivikram, W. Ubachs, M Schlosser, E. J. SalumbidesAbstract:The hydrogen molecule has become a test ground for quantum electrodynamical calculations in molecules. Expanding beyond studies on stable hydrogenic species to the heavier radioactive tritium-bearing molecules, we report on a measurement of the Fundamental T2 Vibrational splitting (v=0→1) for J=0-5 rotational levels. Precision frequency metrology is performed with high-resolution coherent anti-Stokes Raman spectroscopy at an experimental uncertainty of 10-12 MHz, where sub-Doppler saturation features are exploited for the strongest transition. The achieved accuracy corresponds to a 50-fold improvement over a previous measurement, and it allows for the extraction of relativistic and QED contributions to T2 transition energies.
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:Quantum electrodynamics (QED), the fully quantizedand relativistic version of electromagnetism, solvesthe problem of infinities associated with chargedpointlike particles and includes the effects of spontaneousparticle-antiparticle generation from the vacuum. QED istested to extreme precision by comparing values for theelectromagnetic coupling constant obtained from mea-surements of the g factor of the electron [1] and frominterferometric atomic recoil measurements [2]. Theseexperiments and the Lamb shift measurements in atomichydrogen [3,4] have made QED the most accurately testedtheory in physics. Concerning molecules, significantprogress has been made recently in theoretical [5] andexperimental [6,7] investigations of QED phenomena inthe HD
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, M. L. Niu, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:The Fundamental ground tone Vibration of H(2), HD, and D(2) is determined to an accuracy of 2×10(-4) cm(-1) from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless Vibrational splitting is derived from the combination difference between electronic excitation from the X(1)Σ(g)(+), v=0, and v=1 levels to a common EF(1)Σ(g)(+), v=0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system.
H Uitenbroek - One of the best experts on this subject based on the ideXlab platform.
-
the co Fundamental Vibration rotation lines in the solar spectrum ii non lte transfer modeling in static and dynamic atmospheres
The Astrophysical Journal, 2000Co-Authors: H UitenbroekAbstract:We present a numerical method for solving radiative transfer in molecular Vibration-rotation bands that allows for departures from local thermodynamic equilibrium (LTE) while accurately including a large number of lines. The method is applied to the formation of the CO Fundamental Vibration-rotation bands in several plane-parallel hydrostatic models and in a sequence of 20 snapshots from a radiation-hydrodynamics simulation of chromospheric dynamics. Calculations for the hydrostatic models performed with different values of the collisional coupling between different Vibrational states confirm earlier results in the literature showing that the CO lines have LTE source functions in the solar atmosphere, so emergent CO intensities reflect actual temperatures therein. Only if the canonical collisional strengths are too large by more than 2 orders of magnitude would it be possible to explain the low temperatures derived from CO line core intensities at the solar limb by scattering in an atmosphere with much higher temperatures, consistent with the values derived from UV line and continuum and Ca II resonance line diagnostics. An interesting feature in the wavelength structure of the CO Vibration-rotation bands is pointed out, in which pairs of lines can be found in different bands but of similar strength and wavelength. In principle such pairs provide a diagnostic for departures from LTE in the CO lines. CO line core intensity variations computed from the sequence of dynamical snapshots, which represent a typical episode in the chromospheric dynamics simulation, have an amplitude that is 2.5 times higher than observed. It is shown that this large amplitude is due in part to the up and down shift of the CO line formation region during the evolution of the atmosphere and is related to the assumption of instantaneous chemical equilibrium that was assumed to calculate CO concentrations. This suggests that the CO concentration is not in equilibrium, may be lower than would be expected on the basis of chemical equilibrium at the time-averaged mean temperature of the atmosphere, and may have reduced variations compared to instantaneous chemical equilibrium values at the local temperatures.
-
the co Fundamental Vibration rotation lines in the solar spectrum i imaging spectroscopy and multidimensional lte modeling
The Astrophysical Journal, 2000Co-Authors: H UitenbroekAbstract:Spectroscopic imaging observations of the CO Fundamental Vibration-rotation transitions at 4.6 μm, obtained at the Kitt Peak McMath-Pierce facility, show that the dynamics of both the solar granulation and, to a lesser extent, the 5 minute oscillations play an important role in CO line formation. Spectroheliograms made in the cores of strong CO lines display an inverted granular contrast with dark areas corresponding to granule centers and a bright network corresponding to the intergranular lanes. This observation is confirmed by multidimensional radiative transfer modeling of CO line formation in a solar convection-simulation snapshot. Unfortunately, current granulation simulations do not extend to high enough layers in the atmosphere to model formation of CO lines into the chromosphere and close to the solar limb where they exhibit their anomalous temperature behavior. The presented transfer calculations facilitate the interpretation of the observed pattern, predicting that the darkest CO line cores at disk center are associated with the strong adiabatic expansion and cooling that occurs over granule centers when warm upflowing material runs into the steep density gradient of the stable layer above the photosphere. The calculated granulation intensity contrast in the CO line cores is considerably higher than observed, and the calculated spatially averaged line profiles at disk center are deeper than the observed ones. It is speculated that both discrepancies result from the assumption of instantaneous chemical equilibrium which may not be valid in the convective flows. If the CO concentration in the hot convective upflow cannot increase fast enough to adjust to the lower temperatures in the radiatively cooled layer above the photosphere, CO lines would form deeper in the atmosphere, have higher core intensities, and show less contrast, more in agreement with observations.
E. J. Salumbides - One of the best experts on this subject based on the ideXlab platform.
-
relativistic and qed effects in the Fundamental Vibration of t2
Physical Review Letters, 2018Co-Authors: Madhu T Trivikram, W. Ubachs, M Schlosser, E. J. SalumbidesAbstract:The hydrogen molecule has become a test ground for quantum electrodynamical calculations in molecules. Expanding beyond studies on stable hydrogenic species to the heavier radioactive tritium-bearing molecules, we report on a measurement of the Fundamental T2 Vibrational splitting (v=0→1) for J=0-5 rotational levels. Precision frequency metrology is performed with high-resolution coherent anti-Stokes Raman spectroscopy at an experimental uncertainty of 10-12 MHz, where sub-Doppler saturation features are exploited for the strongest transition. The achieved accuracy corresponds to a 50-fold improvement over a previous measurement, and it allows for the extraction of relativistic and QED contributions to T2 transition energies.
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:Quantum electrodynamics (QED), the fully quantizedand relativistic version of electromagnetism, solvesthe problem of infinities associated with chargedpointlike particles and includes the effects of spontaneousparticle-antiparticle generation from the vacuum. QED istested to extreme precision by comparing values for theelectromagnetic coupling constant obtained from mea-surements of the g factor of the electron [1] and frominterferometric atomic recoil measurements [2]. Theseexperiments and the Lamb shift measurements in atomichydrogen [3,4] have made QED the most accurately testedtheory in physics. Concerning molecules, significantprogress has been made recently in theoretical [5] andexperimental [6,7] investigations of QED phenomena inthe HD
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, M. L. Niu, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:The Fundamental ground tone Vibration of H(2), HD, and D(2) is determined to an accuracy of 2×10(-4) cm(-1) from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless Vibrational splitting is derived from the combination difference between electronic excitation from the X(1)Σ(g)(+), v=0, and v=1 levels to a common EF(1)Σ(g)(+), v=0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system.
M. J. Burgdorf - One of the best experts on this subject based on the ideXlab platform.
-
Infrared Spectrograph (IRS) Mid‐Infrared Spectroscopy of IRAS F00183−7111
The Astrophysical Journal Supplement Series, 2004Co-Authors: Henrik Spoon, Lee Armus, V. Charmandaris, J. V. Keane, P. N. Appleton, Harry Teplitz, J. E. Chiar, Eric Peeters, Jordi Camí, Alexander G. G. M. Tielens, M. J. BurgdorfAbstract:We report the detection of strong absorption and weak emission features in the 4-27 μm Spitzer Infrared Spectrograph (IRS) spectrum of the distant ultraluminous infrared galaxy IRAS F00183-7111 ( z = 0.327). The absorption features of CO 2 and CO gas, water ice, hydrocarbons, and silicates are indicative of a strongly obscured ( A 9.6 ≥ 5.4; A V ≥ 90) and complex line of sight through both the hot diffuse interstellar medium and shielded cold molecular clouds toward the nuclear power source. From the profile of the 4.67 μm CO Fundamental Vibration mode, we deduce that the absorbing gas is dense ( n ~ 10 6 cm -3 ) and warm (720 K) and has a CO column density of ~10 19.5 cm -2 , equivalent to N H ~ 10 23.5 cm -2 . The high temperature and density, as well as the small inferred size (
G. D. Dickenson - One of the best experts on this subject based on the ideXlab platform.
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:Quantum electrodynamics (QED), the fully quantizedand relativistic version of electromagnetism, solvesthe problem of infinities associated with chargedpointlike particles and includes the effects of spontaneousparticle-antiparticle generation from the vacuum. QED istested to extreme precision by comparing values for theelectromagnetic coupling constant obtained from mea-surements of the g factor of the electron [1] and frominterferometric atomic recoil measurements [2]. Theseexperiments and the Lamb shift measurements in atomichydrogen [3,4] have made QED the most accurately testedtheory in physics. Concerning molecules, significantprogress has been made recently in theoretical [5] andexperimental [6,7] investigations of QED phenomena inthe HD
-
Fundamental Vibration of molecular hydrogen
Physical Review Letters, 2013Co-Authors: G. D. Dickenson, M. L. Niu, E. J. Salumbides, K. S. E. Eikema, Krzysztof Pachucki, Jacek Komasa, W. UbachsAbstract:The Fundamental ground tone Vibration of H(2), HD, and D(2) is determined to an accuracy of 2×10(-4) cm(-1) from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless Vibrational splitting is derived from the combination difference between electronic excitation from the X(1)Σ(g)(+), v=0, and v=1 levels to a common EF(1)Σ(g)(+), v=0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system.
