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Jens-Uwe Grabow

Bio: Jens-Uwe Grabow is an academic researcher from Leibniz University of Hanover. The author has contributed to research in topics: Rotational spectroscopy & Hyperfine structure. The author has an hindex of 31, co-authored 202 publications receiving 3801 citations. Previous affiliations of Jens-Uwe Grabow include University of Valladolid & University of Kiel.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the design, performance, and operation of a broadband (3-26.5 GHz) high-resolution microwave spectrometer is described, where a coaxially oriented beam resonator arrangement (COBRA) is formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas.
Abstract: The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier‐transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase‐inversion scheme and the low‐noise receiving system employing image‐rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in h...

505 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented a miniaturized version of the Fourier transform microwave (FTMW) spectrometer for analytical chemists, which was mounted on a mobile cart.
Abstract: M. D. Harmony, K. A. Beran, D. M. Angst, and K. L. Ratzlaff [Rev. Sci. Instrum. 66, 5196 (1995)] recently published some design specifications for a smaller version of a Fourier transform microwave (FTMW) spectrometer. In that work they used a nozzle arrangement which pulsed the molecular beam perpendicular to the axis of the Fabry–Perot cavity. They found that even though the size of the vacuum chamber and Fabry–Perot cavity mirrors had been reduced, the overall sensitivity of the instrument was nearly the same as one with a conventional sized resonator. In an effort to establish FTMW spectroscopy as a viable new technique for analytical chemists, we have constructed a miniaturized version of our laboratory instrument for use as an analytical instrument. The vacuum chamber of the instrument is based on a commercially available, multiport 30 cm (12 in.) sphere. An integral end-flange mirror permits a coaxial nozzle injection of the molecular beam which greatly improves the sensitivity of the instrument. The movable cavity mirror rides on a fast motorized stage which allows tuning to any frequency within the range of the spectrometer in 1–2 s. The entire spectrometer is mounted on a mobile cart, allowing it to be easily transported to other laboratories or remote locations. The per-pulse sensitivity of this smaller instrument is slightly less than the larger laboratory instruments, however the smaller vacuum chamber allows the nozzle to be pulsed much faster without overloading the vacuum pumps. The new miniaturized FTMW spectrometer is only a factor of 2 less sensitive than the larger laboratory instrument. This instrument provides analytical chemists with a new tool that can unambiguously identify trace amounts of large organic compounds in gas streams. The instrument also permits real-time analysis which should be useful for monitoring and optimization of process gas streams. Lower detection limits are typically in the nanomol/mol regime.

157 citations

Journal ArticleDOI
TL;DR: The high-resolution rotational spectrum of corannulene has been obtained by Fourier transform microwave spectroscopy, and the dipole moment of this exceptionally polar PAH has been measured by exploiting the Stark effect.
Abstract: Polycyclic aromatic hydrocarbons (PAHs) have long been postulated as constituents of the interstellar gas and circumstellar disks. Observational infrared emission spectra have been plausibly interpreted in support of this hypothesis, but the small (or zero) dipole moments of planar, unsubstituted PAHs preclude their definitive radio astronomical identification. Polar PAHs, such as corannulene, thus represent important targets for radio astronomy because they offer the possibilities of confirming the existence of PAHs in space and revealing new insight into the chemistry of the interstellar medium. Toward this objective, the high-resolution rotational spectrum of corannulene has been obtained by Fourier transform microwave spectroscopy, and the dipole moment (2.07 D) of this exceptionally polar PAH has been measured by exploiting the Stark effect.

146 citations

Journal ArticleDOI
TL;DR: In this article, the authors present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB•MWFT) spectrometer used in the Kiel microwave group.
Abstract: We present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB‐MWFT) spectrometer used in the Kiel microwave group. We emphasize an automatic scanning facility which greatly increases the efficiency of MB‐MWFT spectroscopy for the measurement of unassigned spectra.

137 citations

Journal ArticleDOI
TL;DR: In this article, a number of low-J rotational transitions have been measured for two conformations of the simplest amino acid, glycine, providing precise hyperfine transition frequencies and electric dipole moments for radioastronomy searches for glycine in interstellar clouds.
Abstract: A number of low-J rotational transitions have been measured for two conformations of the simplest amino acid, glycine, providing precise hyperfine transition frequencies and electric dipole moments for radioastronomy searches for glycine in interstellar clouds. Measurements were made between 12 and 25 GHz with a pulsed-nozzle, Fabry-Perot-cavity, Fourier transform microwave spectrometer equipped with either a heated nozzle or laser ablation-nozzle for vaporization of solid phase glycine. Nuclear quadrupole coupling constants were determined for both conformers from measurements of the hyperfine-split rotational transitions. The quadrupole coupling constants for conformer I are eQqaa = -1.208(9) MHz and eQqbb = -0.343(8) MHz and for conformer II are eQqaa = 1.773(2) MHz and eQqbb = -3.194(4) MHz. The dipole moment components of both conformers were determined to higher precision. We obtain μa = 3.039(10) × 10-30 C m [0.911(3)D] and μb = 2.025(17) × 10-30 C m [0.607(5) D] for conformer I, and μa = 17.92(11) × 10-30 C m [5.372(34)D] and μb = 3.10(3) × 10-30 C m [0.93(1)D] for conformer II, where the uncertainties shown are 1 standard deviation.

116 citations


Cited by
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Journal ArticleDOI
TL;DR: The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.
Abstract: The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

2,582 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
TL;DR: The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorptionCross-sections, and associated database management software.
Abstract: This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments. (C) 2003 Elsevier Ltd. All rights reserved.

1,231 citations

01 Jan 1958
TL;DR: In this article, it was shown that the effects of zero point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0.
Abstract: Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

839 citations