The Experts below are selected from a list of 32022 Experts worldwide ranked by ideXlab platform
David A. Ritchie - One of the best experts on this subject based on the ideXlab platform.
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high resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser
Applied Physics Letters, 2006Co-Authors: Heinz-wilhelm Hübers, Alexey Semenov, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, Heiko Richter, S G Pavlov, David A. RitchieAbstract:The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.
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high resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser
Applied Physics Letters, 2006Co-Authors: Heinz-wilhelm Hübers, Alexey Semenov, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, Heiko Richter, S G Pavlov, David A. RitchieAbstract:The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.
E A Bergin - One of the best experts on this subject based on the ideXlab platform.
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Herschel observations of extra-ordinary sources: Detection of Hydrogen Fluoride in absorption towards Orion KL
2020Co-Authors: ⋆ T G Phillips, M Emprechtinger, D C Lis, E A Bergin, T A Bell, D A Neufeld, S Wang, N R Crockett, G A Blake, E CauxAbstract:ABSTRACT We report a detection of the fundamental Rotational Transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules ("weeds"), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 × 10 13 cm −2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H 2 column density within the low-velocity molecular outflow, we obtain a lower limit of ∼ 1.6 × 10 −10 for the HF abundance relative to hydrogen nuclei, corresponding to ∼ 0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J=2-1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 × 10 −9 derived by Neufeld et al
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variable h 13 co emission in the im lup disk x ray driven time dependent chemistry
The Astrophysical Journal, 2017Co-Authors: Ilsedore L Cleeves, E A Bergin, Karin I Oberg, Sean M Andrews, David J Wilner, Ryan A LoomisAbstract:We report the first detection of a substantial brightening event in an isotopologue of a key molecular ion, HCO+, within a protoplanetary disk of a T Tauri star. The H13CO+ Rotational Transition was observed three times toward IM Lup between 2014 July and 2015 May with the Atacama Large Millimeter/submillimeter Array. The first two observations show similar spectrally integrated line and continuum fluxes, while the third observation shows a doubling in the disk-integrated line flux compared to the continuum, which does not change between the three epochs. We explore models of an X-ray active star irradiating the disk via stellar flares, and find that the optically thin H13CO+ emission variation can potentially be explained via X-ray-driven chemistry temporarily enhancing the HCO+ abundance in the upper layers of the disk atmosphere during large or prolonged flaring events. If the HCO+ enhancement is indeed caused by an X-ray flare, future observations should be able to spatially resolve these events and potentially enable us to watch the chemical aftermath of the high-energy stellar radiation propagating across the face of protoplanetary disks, providing a new pathway to explore ionization physics and chemistry, including electron density, in disks.
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variable h13co emission in the im lup disk x ray driven time dependent chemistry
The Astrophysical Journal, 2017Co-Authors: Ilsedore L Cleeves, E A Bergin, Karin I Oberg, Sean M Andrews, David J Wilner, Ryan A LoomisAbstract:We report the first detection of a substantial brightening event in an isotopologue of a key molecular ion, HCO+, within a protoplanetary disk of a T Tauri star. The H13CO+ Rotational Transition was observed three times toward IM Lup between 2014 July and 2015 May with the Atacama Large Millimeter/submillimeter Array. The first two observations show similar spectrally integrated line and continuum fluxes, while the third observation shows a doubling in the disk-integrated line flux compared to the continuum, which does not change between the three epochs. We explore models of an X-ray active star irradiating the disk via stellar flares, and find that the optically thin H13CO+ emission variation can potentially be explained via X-ray-driven chemistry temporarily enhancing the HCO+ abundance in the upper layers of the disk atmosphere during large or prolonged flaring events. If the HCO+ enhancement is indeed caused by an X-ray flare, future observations should be able to spatially resolve these events and potentially enable us to watch the chemical aftermath of the high-energy stellar radiation propagating across the face of protoplanetary disks, providing a new pathway to explore ionization physics and chemistry, including electron density, in disks.
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variable h 13 co emission in the im lup disk x ray driven time dependent chemistry
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Ilsedore L Cleeves, E A Bergin, Karin I Oberg, Sean M Andrews, David J Wilner, Ryan A LoomisAbstract:We report the first detection of a substantial brightening event in an isotopologue of a key molecular ion, HCO$^+$, within a protoplanetary disk of a T Tauri star. The H$^{13}$CO$^+$ $J=3-2$ Rotational Transition was observed three times toward IM Lup between July 2014 and May 2015 with the Atacama Large Millimeter Array. The first two observations show similar spectrally integrated line and continuum fluxes, while the third observation shows a doubling in the disk integrated $J=3-2$ line flux compared to the continuum, which does not change between the three epochs. We explore models of an X-ray active star irradiating the disk via stellar flares, and find that the optically thin H$^{13}$CO$^+$ emission variation can potentially be explained via X-ray driven chemistry temporarily enhancing the HCO$^+$ abundance in the upper layers of the disk atmosphere during large or prolonged flaring events. If the HCO$^+$ enhancement is indeed caused by a X-ray flare, future observations should be able to spatially resolve these events and potentially enable us to watch the chemical aftermath of the high-energy stellar radiation propagating across the face of protoplanetary disks, providing a new pathway to explore ionization physics and chemistry, including electron density, in disks.
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herschel observations of extra ordinary sources hexos detection of hydrogen fluoride in absorption towards orion kl
Astronomy and Astrophysics, 2010Co-Authors: T G Phillips, M Emprechtinger, D C Lis, E A Bergin, T A Bell, D A Neufeld, S Wang, N R Crockett, G A Blake, E CauxAbstract:We report a detection of the fundamental Rotational Transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules (“weeds”), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 × 10^(13) cm^(-2) for the HF column density responsible for the broad absorption component. Using our best estimate of the H_2 column density within the low-velocity molecular outflow, we obtain a lower limit of ~1.6 × 10^(-10) for the HF abundance relative to hydrogen nuclei, corresponding to ~0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J = 2–1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 × 10^(-9) derived by Neufeld et al. for cold, foreground clouds on the line of sight towards G10.6-0.4.
Rui Zheng - One of the best experts on this subject based on the ideXlab platform.
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investigating the influence of intramolecular bond lengths on the intermolecular interaction of h2 agcl complex binding energy intermolecular vibrations and isotope effects
Journal of Chemical Physics, 2019Co-Authors: Limin Zheng, Rui Zheng, Minghui YangAbstract:In this paper, we performed a theoretical study on the influence of intramolecular bond lengths on the intermolecular interactions between H2 and AgCl molecules. Using four sets of bond lengths for the monomers of H2 and AgCl, four-dimensional intermolecular potential energy surfaces (PESs) were constructed from ab initio data points at the level of single and double excitation coupled cluster method with noniterative perturbation treatment of triple excitations. A T-shaped global minimum was found on the PES. Interestingly, both the binding energies and Ag–H2 distances present a linear relationship with the intramolecular bond lengths of H2–AgCl. The accuracy of these PESs was validated by the available spectroscopic data via the bound state calculations, and the predicted Rotational Transition frequencies can reproduce the experimental observations with a root-mean-squared error of 0.0003 cm−1 based on the PES constructed with r(H–H) and r(Ag–Cl) fixed at 0.795 and 2.261 A, respectively. The intermolecular vibrational modes were assigned unambiguously with a simple pattern by analyzing the wave functions. Isotope effects were also investigated by the theoretical calculations, and the results are in excellent agreement with the available spectroscopic data. The Transition frequencies for the isotopolog D2–AgCl are predicted with the accuracy of 0.3 MHz.In this paper, we performed a theoretical study on the influence of intramolecular bond lengths on the intermolecular interactions between H2 and AgCl molecules. Using four sets of bond lengths for the monomers of H2 and AgCl, four-dimensional intermolecular potential energy surfaces (PESs) were constructed from ab initio data points at the level of single and double excitation coupled cluster method with noniterative perturbation treatment of triple excitations. A T-shaped global minimum was found on the PES. Interestingly, both the binding energies and Ag–H2 distances present a linear relationship with the intramolecular bond lengths of H2–AgCl. The accuracy of these PESs was validated by the available spectroscopic data via the bound state calculations, and the predicted Rotational Transition frequencies can reproduce the experimental observations with a root-mean-squared error of 0.0003 cm−1 based on the PES constructed with r(H–H) and r(Ag–Cl) fixed at 0.795 and 2.261 A, respectively. The intermolecu...
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theoretical studies of three dimensional potential energy surfaces using neural networks and Rotational spectra of the ar n 2 complex
Molecular Physics, 2016Co-Authors: Rui Zheng, Limin ZhengAbstract:A new three-dimensional potential energy surface (PES) of the Ar-N-2 van der Waals complex is constructed using the neural network method based on ab initio data points at the CCSD(T) level. The aug-cc-pVQZ basis set is employed for all atoms with midbond functions. The vibrationally averaged PES V-00 is characterised by a global T-shaped minimum which occurs at R= 3.715 angstrom, = 90.0 degrees with a well depth of 98.779 cm(-1). Based on our three-dimensional PES, bound-state calculations are performed for three isotopomers of Ar-N-14(2), Ar-N-15(2), and Ar-(NN)-N-14-N-15, and several intermolecular vibrational states are assigned by analysing the wavefunctions. Moreover, the averaged structural parameters are calculated and the pure Rotational Transition frequencies with J = 0--6 are predicted. The spectroscopic constants are determined by fitting the Rotational energy levels. The theoretical results are in good agreement with experimental data and this work gives more accurate results than those determined previously for the Ar-N-2 complex.
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Rotational spectra of the ne n 2 complex based on a new three dimensional potential energy surface using neural networks
Journal of Molecular Spectroscopy, 2016Co-Authors: Rui Zheng, Limin ZhengAbstract:A new three-dimensional potential energy surface (PES) of the Ne-N-2 van der Waals complex was constructed using the neural networks method based on ab initio data points at the CCSD(T) level. The augcc-pVQZ basis set was employed for all atoms, supplemented by midbond functions. The vibrationally averaged PES V-00 is characterized by a global T-shaped minimum which occurs at R = 3.385 angstrom, 0 = 90.0 degrees with a well depth of -49.202 cm(-1). Based on our three-dimensional PES, bound state calculations were performed for four isotopologues, i.e. Ne-20-N-14(2), Ne-22-N-14(2), Ne-20-N-15(2), Ne-22-N-15(2), and several intermolecular vibrational states were assigned by analyzing the wavefunctions. Moreover, the averaged structural parameters were determined and the pure Rotational Transition frequencies with J = 0-5 are predicted. The spectroscopic constants were determined by fitting the Rotational energy levels. The theoretical results are in good agreement with experimental data and this work gives more accurate results than those determined previously for the Ne-N-2 complex. (C) 2015 Elsevier Inc. All rights reserved.
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theoretical studies for the n2 n2o van der waals complex the potential energy surface intermolecular vibrations and Rotational Transition frequencies
Journal of Chemical Physics, 2011Co-Authors: Limin Zheng, Rui Zheng, Minghui YangAbstract:Theoretical studies of the potential energy surface (PES) and bound states are performed for the N-2-N2O van der Waals (vdW) complex. A four-dimensional intermolecular PES is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. Two equivalent T-shaped global minima are located, in which the O atom of N2O monomer is near the N-2 monomer. The intermolecular fundamental vibrational states are assigned by inspecting the orientation of the nodal surface of the wavefunctions. The calculated frequency for intermolecular disrotation mode is 23.086 cm(-1), which is in good agreement with the available experimental data of 22.334 cm(-1). A negligible tunneling splitting with the value of 4.2 MHz is determined for the ground vibrational state and the tunneling splitting increases as the increment of the vibrational frequencies. Rotational levels and Transition frequencies are calculated for both isotopomers N-14(2)-N2O and 15N(2)-N2O. The accuracy of the PES is validated by the good agreement between theoretical and experimental results for the Transition frequencies and spectroscopic parameters. (C) 2015 AIP Publishing LLC.
Heinz-wilhelm Hübers - One of the best experts on this subject based on the ideXlab platform.
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high resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser
Applied Physics Letters, 2006Co-Authors: Heinz-wilhelm Hübers, Alexey Semenov, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, Heiko Richter, S G Pavlov, David A. RitchieAbstract:The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.
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high resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser
Applied Physics Letters, 2006Co-Authors: Heinz-wilhelm Hübers, Alexey Semenov, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, Heiko Richter, S G Pavlov, David A. RitchieAbstract:The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a Rotational Transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.
Stephan Schlemmer - One of the best experts on this subject based on the ideXlab platform.
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high resolution double resonance action spectroscopy in ion traps vibrational and Rotational fingerprints of ch2nh2
Physical Chemistry Chemical Physics, 2019Co-Authors: Charles R Markus, S Thorwirth, Oskar Asvany, Stephan SchlemmerAbstract:By applying various action spectroscopic techniques in a 4 K cryogenic ion trap instrument, protonated methanimine, CH2NH2+, has been investigated by high-resolution rovibrational and pure Rotational spectroscopy for the first time. In total, 39 rovibrational Transitions within the fundamental band of the ν2 symmetric C-H stretch were measured around 3026 cm-1, which were used to predict pure Rotational Transition frequencies of CH2NH2+ in the ground vibrational state. Based on these predictions, nine Rotational Transitions were observed between 109 and 283 GHz using a novel double resonance method, which significantly improved the sensitivity of the Rotational measurements. This double resonance method consists of Rotational excitation followed by vibrational excitation, which is finally detected as a dip in the number of CH2NH2+-He complexes formed in the 4 K He bath of the trap. The new measurements and the derived predictions of pure Rotational Transitions will enable the first radio-astronomical search for CH2NH2+.
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high resolution double resonance action spectroscopy in ion traps vibrational and Rotational fingerprints of ch 2 nh 2
Physical Chemistry Chemical Physics, 2019Co-Authors: Charles R Markus, S Thorwirth, Oskar Asvany, Stephan SchlemmerAbstract:By applying various action spectroscopic techniques in a 4 K cryogenic ion trap instrument, protonated methanimine, CH2NH2+, has been investigated by high-resolution rovibrational and pure Rotational spectroscopy for the first time. In total, 39 rovibrational Transitions within the fundamental band of the ν2 symmetric C-H stretch were measured around 3026 cm-1, which were used to predict pure Rotational Transition frequencies of CH2NH2+ in the ground vibrational state. Based on these predictions, nine Rotational Transitions were observed between 109 and 283 GHz using a novel double resonance method, which significantly improved the sensitivity of the Rotational measurements. This double resonance method consists of Rotational excitation followed by vibrational excitation, which is finally detected as a dip in the number of CH2NH2+-He complexes formed in the 4 K He bath of the trap. The new measurements and the derived predictions of pure Rotational Transitions will enable the first radio-astronomical search for CH2NH2+.
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Double resonance Rotational spectroscopy of He-HCO.
Physical chemistry chemical physics : PCCP, 2019Co-Authors: Thomas Salomon, Stephan Schlemmer, Matthias Töpfer, Philipp Schreier, Hiroshi Kohguchi, Leonid A Surin, Oskar AsvanyAbstract:The ground state of He–HCO+ is investigated using a recently developed double resonance technique, consisting of a Rotational Transition followed by a vibrational Transition into a dissociative state. In order to derive precise predictions for the Rotational states, the high resolution infrared predissociation spectroscopy of the v1 C–H stretching mode is revisited. Eleven pure Rotational Transitions are measured via the double resonance method. A least squares fit of these Transitions to a standard linear rotor Hamiltonian reveals that the semirigid rotor model cannot fully describe the loosely bound He–HCO+ complex. The novel double resonance technique is compared with other action spectroscopic schemes, and some potential future applications are presented.
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Rotational state-dependent attachment of He atoms to cold molecular ions: An action spectroscopic scheme for Rotational spectroscopy
Journal of Molecular Spectroscopy, 2017Co-Authors: Sandra Brünken, Lars Kluge, Alexander Stoffels, Jesús Pérez-ríos, Stephan SchlemmerAbstract:Abstract We present a kinetics model description of a newly developed action spectroscopic method for Rotational spectroscopy based on Rotational state-dependent three-body attachment of He atoms to cold molecular ions stored in a cryogenic 22-pole ion trap. The model results from numerical simulations and an approximate analytical expression are compared to measurements of the J = 1 – 0 Rotational Transition of CD + , for which we obtain a refined Transition frequency of 453.5218509(7) GHz. From the analysis of the spectroscopic data recorded at varying experimental conditions, e.g. over a wide range of He number densities and excitation powers, we deduce that the ternary rate coefficient in the first excited Rotational state of CD + is reduced to ( 55 ± 5 ) % of the Rotational ground state value. This decrease in the rate coefficient can be rationalized as an increase of the redissociation probability in the ternary collision process. A summary of Rotational spectroscopy measurements of other molecular ions using the new method will be given, and its general applicability is discussed.
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laboratory Rotational ground state Transitions of nh3d and cf
Astronomy and Astrophysics, 2016Co-Authors: Lars Kluge, Stephan Schlemmer, Alexander Stoffels, Sandra BrünkenAbstract:Aims. This paper reports accurate laboratory frequencies of the Rotational ground state Transitions of two astronomically relevant molecular ions, NH 3 D + and CF + . Methods. Spectra in the millimetre-wave band were recorded by the method of Rotational state-selective attachment of He atoms to the molecular ions stored and cooled in a cryogenic ion trap held at 4 K. The lowest Rotational Transition in the A state (ortho state) of NH 3 D + ( J K = 1 0 −0 0 ), and the two hyperfine components of the ground state Transition of CF + ( J = 1−0) were measured with a relative precision better than 10 -7 . Results. For both target ions, the experimental Transition frequencies agree with recent observations of the same lines in different astronomical environments. In the case of NH 3 D + the high-accuracy laboratory measurements lend support to its tentative identification in the interstellar medium. For CF + the experimentally determined hyperfine splitting confirms previous quantum-chemical calculations and the intrinsic spectroscopic nature of a double-peaked line profile observed in the J = 1−0 Transition towards the Horsehead photon-dominated region (PDR).
