scholarly journals Computational Studies of Coinage Metal Anion M− + CH3X (X = F, Cl, Br, I) Reactions in Gas Phase

Molecules ◽  
2022 ◽  
Vol 27 (1) ◽  
pp. 307
Author(s):  
Fan Wang ◽  
Xiaoyan Ji ◽  
Fei Ying ◽  
Jiatao Zhang ◽  
Chongyang Zhao ◽  
...  
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Halogen Bond ◽  
Stationary Points ◽  
Back Side ◽  
Front Side ◽  
Coinage Metal ◽  
D10 Metal ◽  
High Transition ◽  
Sn2 Pathway

We characterized the stationary points along the nucleophilic substitution (SN2), oxidative insertion (OI), halogen abstraction (XA), and proton transfer (PT) product channels of M− + CH3X (M = Cu, Ag, Au; X = F, Cl, Br, I) reactions using the CCSD(T)/aug-cc-pVTZ level of theory. In general, the reaction energies follow the order of PT > XA > SN2 > OI. The OI channel that results in oxidative insertion complex [CH3–M–X]− is most exothermic, and can be formed through a front-side attack of M on the C-X bond via a high transition state OxTS or through a SN2-mediated halogen rearrangement path via a much lower transition state invTS. The order of OxTS > invTS is inverted when changing M− to Pd, a d10 metal, because the symmetry of their HOMO orbital is different. The back-side attack SN2 pathway proceeds via typical Walden-inversion transition state that connects to pre- and post-reaction complexes. For X = Cl/Br/I, the invSN2-TS’s are, in general, submerged. The shape of this M− + CH3X SN2 PES is flatter as compared to that of a main-group base like F− + CH3X, whose PES has a double-well shape. When X = Br/I, a linear halogen-bonded complex [CH3−X∙··M]− can be formed as an intermediate upon the front-side attachment of M on the halogen atom X, and it either dissociates to CH3 + MX− through halogen abstraction or bends the C-X-M angle to continue the back-side SN2 path. Natural bond orbital analysis shows a polar covalent M−X bond is formed within oxidative insertion complex [CH3–M–X]−, whereas a noncovalent M–X halogen-bond interaction exists for the [CH3–X∙··M]− complex. This work explores competing channels of the M− + CH3X reaction in the gas phase and the potential energy surface is useful in understanding the dynamic behavior of the title and analogous reactions.

scholarly journals Standard Molar Enthalpies of Formation of Halomethanes Based on Quantum Chemical Computations

2020 ◽  
Author(s):  
Konstantinos Kalamatianos
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Halogen Bond ◽  
Chemical Processes ◽  
Enthalpies Of Formation ◽  
Isodesmic Reaction ◽  
Gold Standard Method ◽  
Ozone Destruction ◽  
Quantum Chemical Computations ◽  
Reaction Schemes

Accurate calculations of standard molar enthalpies of formation (ΔΗf°)m(g) and carbon-halogen bond dissociation enthalpies, BDE, of a variety of halomethanes with relevance on several atmospheric chemical processes and particularly to ozone destruction, were performed in the gas phase at 298.15 K. The (ΔΗf°)m(g) of the radicals formed through bond dissociations have also been computed. Ab initio computational methods and isodesmic reaction schemes were used. It is found that for the large majority of these species, the gold standard method of quantum chemistry (CCSD(T)) and even MP2 are capable to predict enthalpy values nearing chemical accuracy provided that isodesmic reaction schemes are used. New estimates for standard molar enthalpies of formation and BDE are suggested including for species that to our knowledge there are no experimental (ΔΗf°)m(g) (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) or BDE values (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) available in the literature. The method and calculational procedures presented may profitably be used to obtain accurate (ΔΗf°)m(g) and BDE values for these species.

The Mechanism of J-V “Roll-Over” in CdS/CdTe Devices

2007 ◽  
Vol 1012 ◽  
Author(s):  
Jie Zhou ◽  
Xuanzhi Wu ◽  
Yanfa Yan ◽  
Sally Asher ◽  
Juarez Da Silva ◽  
...  
Keyword(s):  
Back Side ◽  
Back Contact ◽  
Front Side ◽  
Current Voltage

AbstractThe “roll-over” phenomenon in current-voltage (J-V) curves of CdS/CdTe devices is recognized as a result of the formation of a higher back barrier. When Cu has not been intentionally added to the back contact, roll-over is understandable. However, the mechanism was unclear for forming J-V roll-over in a CdTe cell with a back contact containing Cu. We did extensive characterizations, including XRD, XPS, SIMS, TEM, and EDS, and “recontact” experiments to understand this phenomenon. The results show that the roll-over comes from the formation of Cu-related oxides at the back side of the device during processing, rather than the diffusion of Cu to the front side of the device. Discussions related to the J-V roll-over mechanisms will also be presented.

A Novel Silicon Base Piezoresistive Pressure Sensor Using Front Side Etching Process

2003 ◽  
Author(s):  
Chih-Tang Peng ◽  
Ji-Cheng Lin ◽  
Chun-Te Lin ◽  
Kuo-Ning Chiang ◽  
Jin-Shown Shie
Keyword(s):  
Pressure Sensor ◽  
Thermal Loading ◽  
Fabrication Process ◽  
Back Side ◽  
The Novel ◽  
Front Side ◽  
Sensor Performance ◽  
Novel Structure ◽  
Piezoresistive Pressure Sensor ◽  
Packaging Structure

By applying the etching via technology, this study proposes a novel front-side etching fabrication process for a silicon based piezoresistive pressure sensor to replace the conventional backside bulk micro-machining. The distinguishing features of this novel structure are chip size reduction and fabrication costs degradation. In order to investigate the sensor performance and the sensor packaging effect of the structure proposed in this research, the finite element method was adopted for analyzing the sensor sensitivity and stability. The sensitivity and the stability of the novel sensor after packaging were studied by applying mechanical as well as thermal loading to the sensor. Furthermore, the fabrication process and the sensor performance of the novel pressure sensor were compared with the conventional back-side etching type pressure sensor for the feasibility validation of the novel sensor. The results showed that the novel pressure sensor provides better sensitivity than the conventional one, and the sensor output signal stability can be enhanced by better packaging structure designs proposed in this study. Based on the above findings, this novel structure pressure sensor shows a high potential for membrane type micro-sensor application.

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