Ethyl cation transfer from diethylchloronium to alkyl aromatics studied by high pressure mass spectrometry

1988 ◽  
Vol 66 (5) ◽  
pp. 1239-1248
Author(s):  
Peggy Jane Mathews ◽  
John A. Stone
Keyword(s):  
High Pressure ◽  
Temperature Coefficient ◽  
Rate Constants ◽  
Negative Temperature ◽  
Ion Source ◽  
Positive Temperature ◽  
Reaction Rate Constants ◽  
Benzene Toluene ◽  
Double Well Potential ◽  
Ethyl Cation

Diethylchloronium (C2H5)2Cl+) has been formed in a high pressure (2–4 Torr) ion source using a C2H5Cl/CH4 mixture. (C2H5)2Cl+ reacts with C2H5Cl (Ea = 22 ± 2 kcal mol−1) at temperatures above 500 K to give [Formula: see text]. The reaction of (C2H5)2Cl+ with B (B = benzene, toluene, isopropylbenzene, mesitylene) yields mainly C2H5B+ at temperatures below 500 K but BH+ is also formed at higher temperatures. The further reactions of C2H5B+ include proton transfer to B yielding BH+ (mesitylene), hydride transfer from B (isopropylbenzene), and reaction with C2H5Cl+ (C2H5)2B+ (toluene and benzene) and (C2H5)3B+ (benzene). The rate constants for the reaction (C2H5)2Cl+ + B → C2H5B+ + C2H5B+ + C2H5Cl increase in the order of increasing reaction exothermicity (mesitylene > isopropylbenzene > toluene > benzene). Mesitylene has a negative temperature coefficient, isopropylbenzene has no temperature coefficient, and toluene and benzene show positive temperature coefficients of reaction rate constants consistent with the double well potential theory for gas phase SN2 reactions.

The gas phase ion chemistry and proton affinity of hexamethyldisiloxane studied by high pressure mass spectrometry

1987 ◽  
Vol 65 (10) ◽  
pp. 2454-2460 ◽  
Author(s):  
Xiaoping Li ◽  
John Alfred Stone
Keyword(s):  
Proton Transfer ◽  
Proton Affinity ◽  
Rate Constants ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Ion Source ◽  
Positive Temperature ◽  
Ion Chemistry ◽  
Gas Phase Ion Chemistry ◽  
Proton Transfer Reactions

The ion chemistry of hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, HMDS) has been studied under chemical ionization conditions at ion source temperatures of 300–600 K and pressures of 2–4 Torr. Highly exothermic proton transfer to HMDS from CH5+ and C2H5+ leads mainly to loss of CH3 but with decreasing exothermicity the yield of HMDSH+ increases such that transfer from t-C4H9+ (ΔH0 = −7.5 kcal mol−1) yields almost exclusively HMDSH+. Although HMDSH+ transfers (CH3)3Si+ rather than a proton to most reference bases, the proton affinity of HMDS has been determined from van't Hoff plots using the equilibrium method with methylaromatics as reference bases. PA(HMDS) = 203.4 kcal mol−1 is in excellent accord with an earlier estimate of 203 kcal mol−1 obtained by the bracketing method. The rate constants for these proton transfer reactions show very large negative temperature coefficients in the exothermic directions which are consistent with the reactions of charge delocalized ions and/or reactions in which considerable loss of rotational freedom occurs along the reaction coordinate. The rate constants in the reverse directions have a positive temperature coefficient only when the endothermicity is significant (>2.5 kcal mol−1).

The gas phase reactivity of chloronium ions by high pressure mass spectroscopy

1984 ◽  
Vol 62 (7) ◽  
pp. 1373-1379 ◽  
Author(s):  
John A. Stone ◽  
William M. Splinter ◽  
Dena E. Splinter
Keyword(s):  
High Pressure ◽  
Temperature Coefficient ◽  
Gas Phase ◽  
Mass Spectroscopy ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Ion Source ◽  
Coefficient Of Reactivity

The reactions of CH3ClCH3+ (I) and CH3ClCH2Cl+ (II) with a range of bases have been studied in a high pressure ion source. Reactant ion monitoring has been used to obtain the relative reactivities. Transfer of CH3+ from I and CH2Cl+ from II are the only reactions observed with N- and O-containing bases. Following addition of CH2Cl+ from II, the lower alkyl aromatics (ArH) yield either ArHCH2Cl+ or the benzyl ions ArCH2+ and ArCHCl+ while CH3+ transfer leads only to ArHCH3+. The reactivities of the alkyl aromatics increase with increasing exothermicity (benzene → mesitylene) and there is an increasingly negative temperature coefficient of reactivity in the same order.

Current-transport mechanism in Au/V-doped PVC+TCNQ/p-Si structures

2015 ◽  
Vol 29 (13) ◽  
pp. 1550076 ◽  
Author(s):  
H. Tecimer ◽  
Ö. Vural ◽  
A. Kaya ◽  
Ş. Altındal
Keyword(s):  
Temperature Coefficient ◽  
Transport Mechanism ◽  
Forward Bias ◽  
Thermionic Emission ◽  
Negative Temperature ◽  
Positive Temperature ◽  
Current Transport ◽  
Insulator Layer ◽  
Zero Bias ◽  
Current Transport Mechanism

The forward and reverse bias current–voltage (I–V) characteristics of Au/V-doped polyvinyl chloride+Tetracyanoquino dimethane/porous silicon (PVC+TCNQ/p-Si) structures have been investigated in the temperature range of 160–340 K. The zero bias or apparent barrier height (BH) (Φ ap = Φ Bo ) and ideality factor (n ap = n) were found strongly temperature dependent and the value of n ap decreases, while the Φ ap increases with the increasing temperature. Also, the Φ ap versus T plot shows almost a straight line which has positive temperature coefficient and it is not in agreement with the negative temperature coefficient of ideal diode or forbidden bandgap of Si (α Si = -4.73×10-4 eV/K ). The high value of n cannot be explained only with respect to interfacial insulator layer and interface traps. In order to explain such behavior of Φ ap and n ap with temperature, Φ ap Versus q/2kT plot was drawn and the mean value of (Φ Bo ) and standard deviation (σs) values found from the slope and intercept of this plot as 1.176 eV and 0.152 V, respectively. Thus, the modified ( ln (Io/T2)-(qσs)2/2(kT)2 versus (q/kT) plot gives the Φ Bo and effective Richardson constant A* as 1.115 eV and 31.94 A ⋅(cm⋅K)-2, respectively. This value of A*( = 31.94 A⋅( cm ⋅K)-2) is very close to the theoretical value of 32 A ⋅(cm⋅K)-2 for p-Si. Therefore, the forward bias I–V–T characteristics confirmed that the current-transport mechanism (CTM) in Au/V-doped PVC+TCNQ/p-Si structures can be successfully explained in terms of the thermionic emission (TE) mechanism with a Gaussian distribution (GD) of BHs at around mean BH.

Temperature Dependence of Impact Ionization Coefficients in 4H-SiC

2014 ◽  
Vol 778-780 ◽  
pp. 461-466 ◽  
Author(s):  
Hiroki Niwa ◽  
Jun Suda ◽  
Tsunenobu Kimoto
Keyword(s):  
Temperature Dependence ◽  
Temperature Coefficient ◽  
Breakdown Voltage ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Impact Ionization ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Ionization Coefficients

Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (Mp) and electrons (Mn), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

scholarly journals S-shooting: a Bennett–Chandler-like method for the computation of rate constants from committor trajectories

2016 ◽  
Vol 195 ◽  
pp. 345-364 ◽  
Author(s):  
Georg Menzl ◽  
Andreas Singraber ◽  
Christoph Dellago
Keyword(s):  
Rate Constants ◽  
Simulation Method ◽  
Free Energy Calculations ◽  
Stable States ◽  
One Dimensional ◽  
Random Walker ◽  
Reaction Rate Constants ◽  
Definition Of ◽  
Double Well Potential ◽  
Condensed Systems

Mechanisms of rare transitions between long-lived stable states are often analyzed in terms of commitment probabilities, determined from swarms of short molecular dynamics trajectories. Here, we present a computer simulation method to determine rate constants from such short trajectories combined with free energy calculations. The method, akin to the Bennett–Chandler approach for the calculation of reaction rate constants, requires the definition of a valid reaction coordinate and can be applied to both under- and overdamped dynamics. We verify the correctness of the algorithm using a one-dimensional random walker in a double-well potential and demonstrate its applicability to complex transitions in condensed systems by calculating cavitation rates for water at negative pressures.

Influence of CF on PTC Properties of LDPE/Carbon Fiber Composites

2014 ◽  
Vol 1056 ◽  
pp. 20-24 ◽  
Author(s):  
Wen Long Zhang ◽  
Yu Ping Wan ◽  
Ya Jie Dai ◽  
Yan Gao ◽  
Chen Wang ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Temperature Coefficient ◽  
Low Cost ◽  
Negative Temperature ◽  
Treatment Method ◽  
Positive Temperature Coefficient ◽  
Carbon Fiber Composites ◽  
Positive Temperature ◽  
Short Lifespan ◽  
Cost Characteristics

PO/CB (Polyolefin/Carbon Black) PTC (Positive Temperature Coefficient) composite with easy processing, low cost characteristics has been applied widely. But it suffered from a relatively short lifespan because of its NTC (Negative Temperature Coefficient) effect and low PTC intensity. In order to overcome this shortcoming, the CF was calcination-treated to prepare LDPE/CF (Low Density Polyethylene/Carbon Fiber) PTC composite. Influence of length, content and treatment method of CF on PTC properties of composites was investigated. Results showed that 0.5mm length CF in composites had higher PTC intensity than that of 2mm length CF. PTC intensity of the composites was enhanced more effectively by calcination treated CF compared to the untreated CF. The maximum PTC intensity was 8.1 when CF’s content was at 8wt%.

The Master Equation for the Dissociation of a Dilute Diatomic Gas. X. How Rotation Causes Low Arrhenius Temperature Coefficients

1973 ◽  
Vol 51 (18) ◽  
pp. 3152-3155 ◽  
Author(s):  
Huw O. Pritchard
Keyword(s):  
Low Temperature ◽  
Temperature Coefficient ◽  
Rate Constants ◽  
Recombination Rate ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Equilibrium Form ◽  
Temperature Coefficients ◽  
Recombination Rate Constant ◽  
Arrhenius Temperature

It is shown that previously calculated nonequilibrium rate constants for the dissociation of H2 and D2 appear to approach a rotationally averaged equilibrium expression at low temperature. This equilibrium form of the rate expression itself has an Arrhenius temperature coefficient for dissociation which is significantly less than the dissociation energy, and the corresponding recombination rate constant has a negative temperature coefficient. The reasons for this are explained.

scholarly journals Development of Auto Thermal Control Device For Space Air - Conditioning

2021 ◽  
pp. 193-204
Author(s):  
Akinde Olusola Kunle ◽  
Maduako Kingsley Obinna ◽  
Akande, Kunle Akinyinka ◽  
Adeaga Oyetunde Adeoye
Keyword(s):  
Temperature Coefficient ◽  
Room Temperature ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Thermal Control ◽  
Positive Temperature Coefficient ◽  
Control Device ◽  
Thermal Source ◽  
Positive Temperature ◽  
Ntc Thermistor

Auto Thermal Control device is an electronic based device which employs the application of temperature sensors to controlling household appliances without human interference directly. In this work, thermal source is used to regulate electrical fan and room heater depending on ambient temperature. The room heater, which is adjusted to a set temperature, switches ‘ON’ when the temperature of a room is low (cold). While the same is switches ‘OFF’ with increase in the room temperature. This triggers ‘ON’ an electric fan at different speeds, and thus cools the room. A temperature sensor, tthermistor, monitors change in room temperature. Two types of thermistor exists: Positive Temperature Coefficient, PTC. An increasee in the resistance of PTC results in increasee in temperature). In the Negative Temperature Coefficient, NTC; a decreasee in resistance yields to temperature increase. This article explored a NTC thermistor. The design could be a ready product in the market of the developing nation where environmental automation is yet fully deployed.

scholarly journals Temperature Self-Compensated Strain Sensors based on MWCNT-Graphene Hybrid Nanocomposite

2019 ◽  
Vol 3 (4) ◽  
pp. 96 ◽  
Author(s):  
Rajarajan Ramalingame ◽  
Jose Roberto Bautista-Quijano ◽  
Danrlei de Farias Alves ◽  
Olfa Kanoun
Keyword(s):  
Temperature Coefficient ◽  
Carbon Nanomaterials ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Gauge Factor ◽  
Positive Temperature ◽  
Hybrid Nanocomposite ◽  
Resistance Change ◽  
Influence Of Temperature ◽  
Dispersion Quality

Sensors based on carbon nanomaterials are gaining importance due to their tunable properties and their potentially outstanding sensing performance. Despite their advantages, carbon-based nanomaterial sensors are prone to cross-sensitivities with environmental factors like temperature. Thus, to reduce the temperature influence on the sensing material, compensation and correction procedures are usually considered. These methods may require the use of additional sensors which can themselves be subject to residual errors. Hence, a more promising approach consists of synthesizing a material that is capable of self-compensating for the influence of temperature. In this study, a hybrid nanocomposite based on multi-walled carbon nanotubes (MWCNT) and graphene is proposed, which can compensate, by itself, for the influence of temperature on the material conductivity. The hybrid nanocomposite material uses the different temperature behavior of MWCNTs, which have a negative temperature coefficient, and graphene, which has a positive temperature coefficient. The influence of the material ratio and dispersion quality are investigated in this work. Material composition and dispersion quality are analyzed using Raman spectroscopy and scanning electron microscopy (SEM). A composition of 70% graphene and 30% MWCNT exhibits a nearly temperature-independent hybrid nanocomposite with a sensitivity of 0.022 Ω/°C, corresponding to a resistance change of ~1.2 Ω for a temperature range of 25 to 80 °C. Additionally, a simple investigation of the strain sensing behavior of the hybrid material is also presented. The hybrid nanocomposite-based, thin-film strain sensor exhibits good stability over 100 cycles and a significantly high gauge factor, i.e., 16.21.

Experimental Verification of a Self-Triggered Solid-State Circuit Breaker Based on a SiC BIFET

2017 ◽  
Vol 897 ◽  
pp. 665-668
Author(s):  
Matthaeus Albrecht ◽  
Andreas Huerner ◽  
Tobias Erlbacher ◽  
Anton J. Bauer ◽  
Lothar Frey
Keyword(s):  
Solid State ◽  
Temperature Coefficient ◽  
High Voltage ◽  
Circuit Breaker ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Solid State Circuit ◽  
Current Voltage ◽  
Solid State Circuit Breaker

In this work, the feasibility of the Bipolar-Injection Field Effect-Transistor (BIFET) [5] in two different Dual Thyristor type circuits [4] for an application as solid-state circuit breaker (SSCB) is experimentally verified. The Dual Thyristor type circuits are assembled from discrete silicon JFETs and a silicon carbide BIFET and are electrically characterized at various temperatures. The current-voltage characteristic shows the expected regenerative self-triggered turn-off capability under over-currents and the option to control the turn-off current by a passive resistor network. The issue with the adverse positive temperature coefficient of the trigger-current can be solved by putting the SiC BIFET in a cascode arrangement with a silicon Dual Thyristor. In this configuration the SiC BIFET provides the high voltage blocking capability and the silicon Dual Thyristor with its negative temperature coefficient controls the trigger-current. Transient analyses of both circuits indicate fast switching times of less than 50 μs seconds. It is demonstrated for the first time, that the SiC BIFET, due to its normally-on behaviour, used in a Dual Thyristor type circuit is a promising concept for self-triggered fuses in high current and high voltage applications.

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