scholarly journals Low Pressure Gas Electron Diffraction: an Experimental Setup and Case Studies

2020 ◽  
Author(s):  
Yury Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter
Keyword(s):  
Electron Diffraction ◽  
Benzoic Acid ◽  
Low Pressure ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Experimental Setup ◽  
Critical Comparison ◽  
Diffraction Patterns ◽  
Predicted Values ◽  
Semi Empirical

<div>Principles of low pressure gas electron diffraction(LPGED) are introduced. An experimental setup has</div><div>been constructed for measuring electron diffraction patterns of gaseous samples at pressures below 10−3</div><div>mbar. Test measurements have been performed for benzoic acid at T = 287 K corresponding to a vapor </div><div>pressure of the substance P = 2 × 10−4 mbar, for iodoform CHI3 at T = 288 K (P = 4 × 10−4 mbar) and for carbon tetraiodide CI4 at T = 290K (P = 1 × 10−4 mbar). Due to the low experimental temperature thermal decomposition of CI4 has been prevented, which was unavoidable in previous classical measurements at higher temperatures.</div><div>From the obtained data the molecular structures have been successfully refined. The most important</div><div>semi-empirical equilibrium molecular parameters are re(Car–Car)av = 1.387(5) Å in benzoic acid, re(C–I)</div><div>= 2.123(3) Å in iodoform and re(C–I) = 2.133(7) Å in carbon tetraiodide. The determined parameters</div><div>showed consistency with theoretically predicted values. A critical comparison with results of the earlier</div><div>investigations has also been done.</div>

scholarly journals Low Pressure Gas Electron Diffraction: an Experimental Setup and Case Studies

2020 ◽  
Author(s):  
Yury Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter
Keyword(s):  
Electron Diffraction ◽  
Benzoic Acid ◽  
Low Pressure ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Experimental Setup ◽  
Critical Comparison ◽  
Diffraction Patterns ◽  
Predicted Values ◽  
Semi Empirical

<div>Principles of low pressure gas electron diffraction(LPGED) are introduced. An experimental setup has</div><div>been constructed for measuring electron diffraction patterns of gaseous samples at pressures below 10−3</div><div>mbar. Test measurements have been performed for benzoic acid at T = 287 K corresponding to a vapor </div><div>pressure of the substance P = 2 × 10−4 mbar, for iodoform CHI3 at T = 288 K (P = 4 × 10−4 mbar) and for carbon tetraiodide CI4 at T = 290K (P = 1 × 10−4 mbar). Due to the low experimental temperature thermal decomposition of CI4 has been prevented, which was unavoidable in previous classical measurements at higher temperatures.</div><div>From the obtained data the molecular structures have been successfully refined. The most important</div><div>semi-empirical equilibrium molecular parameters are re(Car–Car)av = 1.387(5) Å in benzoic acid, re(C–I)</div><div>= 2.123(3) Å in iodoform and re(C–I) = 2.133(7) Å in carbon tetraiodide. The determined parameters</div><div>showed consistency with theoretically predicted values. A critical comparison with results of the earlier</div><div>investigations has also been done.</div>

scholarly journals Combined Gas Electron Diffraction and Mass Spectrometric Experimental Setup at Bielefeld University

2020 ◽  
Author(s):  
Yury Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter ◽  
Oleg A. Pimenov ◽  
Sergey A. Shlykov
Keyword(s):  
Acetic Acid ◽  
Electron Diffraction ◽  
Mass Spectra ◽  
Data Interpretation ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Electron Diffraction Data ◽  
Experimental Setup ◽  
Experimental Conditions ◽  
Diffraction Patterns

We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 and 457 K, respectively. Electron diffraction data have been analysed taking into account mass spectra measured in the same experiments. From the diffraction intensities molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The determined in this work length of the hydrogen bond in the acetic acid dimer, re(O<sup>...</sup>H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend to measure diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction point.<br>

scholarly journals Combined Gas Electron Diffraction and Mass Spectrometric Experimental Setup at Bielefeld University

2020 ◽  
Author(s):  
Yury Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter ◽  
Oleg A. Pimenov ◽  
Sergey A. Shlykov
Keyword(s):  
Acetic Acid ◽  
Electron Diffraction ◽  
Mass Spectra ◽  
Data Interpretation ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Electron Diffraction Data ◽  
Experimental Setup ◽  
Experimental Conditions ◽  
Diffraction Patterns

We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 and 457 K, respectively. Electron diffraction data have been analysed taking into account mass spectra measured in the same experiments. From the diffraction intensities molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The determined in this work length of the hydrogen bond in the acetic acid dimer, re(O<sup>...</sup>H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend to measure diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction point.<br>

scholarly journals Low pressure gas electron diffraction: An experimental setup and case studies

2020 ◽  
Vol 91 (7) ◽  
pp. 074104
Author(s):  
Yury V. Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter
Keyword(s):  
Electron Diffraction ◽  
Case Studies ◽  
Low Pressure ◽  
Gas Electron Diffraction ◽  
Experimental Setup

Combined gas electron diffraction and mass spectrometric experimental setup at Bielefeld University

2020 ◽  
Vol 91 (7) ◽  
pp. 073103
Author(s):  
Yury V. Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter ◽  
Oleg A. Pimenov ◽  
Sergey A. Shlykov
Keyword(s):  
Electron Diffraction ◽  
Mass Spectrometric ◽  
Gas Electron Diffraction ◽  
Experimental Setup

scholarly journals Molecular Structure of Pyrazinamide: a Critical Assessment of Modern Gas Electron Diffraction Data from Three Laboratories

2020 ◽  
Author(s):  
Arseniy A. Otlyotov ◽  
Georgiy V. Girichev ◽  
Anatolii N. Rykov ◽  
Timo Glodde ◽  
Yury Vishnevskiy
Keyword(s):  
Molecular Structure ◽  
Electron Diffraction ◽  
Structure Refinement ◽  
Diffraction Method ◽  
Detailed Examination ◽  
Gas Electron Diffraction ◽  
Electron Diffraction Data ◽  
Data Sets ◽  
Background Elimination ◽  
Diffraction Patterns

<div><div>Accuracy and precision of molecular parameters determined by modern gas electron diffraction method</div><div>have been investigated. Diffraction patterns of gaseous pyrazinamide have been measured independently in three laboratories, in Bielefeld (Germany), Ivanovo (Russia) and Moscow (Russia). All data sets have been analysed in equal manner using highly controlled background elimination procedure and flexible restraints in molecular structure refinement. In detailed examination and comparison of the obtained results we have determined the average experimental precision of 0.004 Å for bond lengths and 0.2 degrees for angles. The corresponding average deviations of the refined parameters from the ae-CCSD(T)/ccpwCVTZ theoretical values were 0.003 Å and 0.2 degrees. The average precision for refined amplitudes of interatomic vibrations was determined to be 0.005 Å. It is recommended to take into account these values in calculations of total errors for refined parameters of other molecules with comparable complexity.</div></div><div><br></div>

scholarly journals The Molecular Structures of Trimethylarsenic, Trimethylantimony and Dimethyltellurium Determined by Gas Electron Diffraction.

1983 ◽  
Vol 37a ◽  
pp. 595-599 ◽  
Author(s):  
Richard Blom ◽  
Arne Haaland ◽  
Ragnhild Seip ◽  
Reijo Mäkelä ◽  
Ulla Kekäläinen
Keyword(s):  
Electron Diffraction ◽  
Molecular Structures ◽  
Gas Electron Diffraction

On Comparing Experimental and Calculated Structural Parameters

1998 ◽  
Author(s):  
Lothar Schäfer ◽  
John D. Ewbank
Keyword(s):  
Electron Diffraction ◽  
Potential Energy ◽  
Ab Initio ◽  
Structural Parameters ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Torsional Angle ◽  
Internuclear Distances ◽  
Molecular Potential Energy ◽  
The One

The tacit assumption underlying all science is that, of two competing theories, the one in closer agreement with experiment is the better one. In structural chemistry the same principle applies but, when calculated and experimental structures are compared, closer is not necessarily better. Structures from ab initio calculations, specifically, must not be the same as the experimental counterparts the way they are observed. This is so because ab initio geometries refer to nonexistent, vibrationless states at the minimum of potential energy, whereas structural observables represent specifically defined averages over distributions of vibrational states. In general, if one wants to make meaningful comparisons between calculated and experimental molecular structures, one must take recourse of statistical formalisms to describe the effects of vibration on the observed parameters. Among the parameters of interest to structural chemists, internuclear distances are especially important because other variables, such as bond angles, dihedral angles, and even crystal spacings, can be readily derived from them. However, how a rigid torsional angle derived from an ab initio calculation compares with the corresponding experimental value in a molecule subject to vibrational anharmonicity, is not so easy to determine. The same holds for the lattice parameters of a molecule in a dynamical crystal, and their temperature dependence as a function of the molecular potential energy surface. In contrast, vibrational effects are readily defined and best described for internuclear distances, bonded and non-bonded ones. In general, all observed internuclear distances are vibrationally averaged parameters. Due to anharmonicity, the average values will change from one vibrational state to the next and, in a molecular ensemble distributed over several states, they are temperature dependent. All these aspects dictate the need to make statistical definitions of various conceivable, different averages, or structure types. In addition, since the two main tools for quantitative structure determination in the vapor phase—gas electron diffraction and microwave spectroscopy—interact with molecular ensembles in different ways, certain operational definitions are also needed for a precise understanding of experimental structures. To illustrate how the operations of an experimental technique affect the nature of its observables, gas electron diffraction shall be used as an example.

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