Geminate-ion kinetics with competing ion fragmentation in nonpolar liquids with halocarbons

1990 ◽  
Vol 68 (9) ◽  
pp. 918-924 ◽  
Author(s):  
Rolf E. Bühler
Keyword(s):  
Low Temperatures ◽  
Pulse Radiolysis ◽  
Room Temperature ◽  
Ion Concentration ◽  
Geminate Recombination ◽  
Rate Law ◽  
Ion Fragmentation ◽  
Nonpolar Liquids ◽  
Ion Recombination ◽  
Semi Empirical

The semi-empirical rate law for geminate-ion recombination by van den Ende, Warman, and Hummel, which predicts a linear dependence of the ion concentration with t−0.6, is modified to include simultaneous ion fragmentation. The theory is applied to the kinetics, as observed by pulse radiolysis of liquid methylcyclohexane (MCH) solutions of N2O, CHCl3, or tert-butylchloride (t-BuCl) at low temperatures. In MCH saturated with N2O (−130 °C), the solvent cation (MCH+, λmax = 550 nm) moves about 400 times faster than prediced by diffusion. With the known conductivity data at room temperature, an activation energy of about 2.7 kJ/mol can be derived. The solvent cation MCH+ does not appear to fragment. With t-BuCl added to MCH (−134 °C), MCH+ (λmax = 550 nm) and t-BuCl− (λmax = 450 nm) are observed simultaneously. The initial kinetics corresponds to the parent ion (MCH+) recombination with t-BuCl−. Then the MCH+ fragmentation with k1(−134 °C) = 3 × 105 s−1 is observed, followed by the geminate recombination of some fragment cation with t-BuCl−. The fragment cation recombines 300 times slower than the parent cation. With CHCl3 added to MCH (−130 °C), the MCH+ absorption is hidden within the [Formula: see text] band (λmax = 470 nm); however, the fragmentation is detected from kinetic analysis to occur in about 2 × 106 s−1. The modified t−0.6 rate law appears to be a very useful tool to study simultaneous ion recombination and ion fragmentation.

Dimethylhalonium-Ionen in Aluminiumhalogenid/Methylhalogenid-Lösungen / Dimethylhalonium-Ions in Aluminium Halide/Methyl Halide Solutions

1979 ◽  
Vol 34 (7) ◽  
pp. 896-899 ◽  
Author(s):  
Peter Brüggeller ◽  
Erwin Mayer
Keyword(s):  
Time Scale ◽  
Low Temperatures ◽  
Room Temperature ◽  
Chemical Shifts ◽  
Ion Concentration ◽  
Molar Ratio ◽  
Lower Field ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Methyl Halide

Abstract Evidence for the formation of (CH3)2Br+ and (CH3)2I+ in CH3Br and CH3I solutions saturated with AlBr3 comes from the appearance of a second singlet in the 1H NMR spectrum. The (CH3)2Br+ ion is formed at -40 °C to about 5 mol%, the (CH3)2I+ ion at -12 °C with 50 mol% yield. At higher temperatures the concentration of the halonium ions decreases rapidly. The (CH3)2Br+ ion is not detectable at room temperature, the concentration of (CH3)2I+ decreases to about 30 mol%. Dilution of the saturated solutions with methyl halide also reduces the halonium ion concentration. An AlBr3/CH3Br solution with a molar ratio of 1:3 at -40 °C shows no sign of (CH3)2Br+ formation in the XH NMR spectrum. Both effects are best explained by formation of dimethylhalonium ions from the adduct CH3X-AIX3 and by dependence of adduct concentration on temperature and dilution. Exchange of (CH3)2Br+ and (CH3)2I+ with methyl halide is slow on the NMR time scale at low temperatures similar to the results in SbF5/SO2. The 1H NMR singlets of (CH3)2Br+ and (CH3)2I+ are shifted to lower field by 1.32 and 1.68 ppm in comparison with the chemical shifts in SbF5/SO2 solution

Ion recombination processes in rigid solutions

1977 ◽  
Vol 55 (11) ◽  
pp. 1867-1875 ◽  
Author(s):  
John R. Miller
Keyword(s):  
Aromatic Hydrocarbon ◽  
Charge Separation ◽  
Pulse Radiolysis ◽  
Room Temperature ◽  
Triplet States ◽  
Trapped Electrons ◽  
Recombination Processes ◽  
Free Ion ◽  
The Matrix ◽  
Ion Recombination

It is known that the free ion yield is small in irradiated aromatic hydrocarbon liquids. This study uses pulse radiolysis to observe anions of aromatic solutes in matrices at 77 K. In aliphatic matrices, trapped electrons tunnel to aromatic solutes and the anion yield is observed to grow with time. If the concentration of aromatic solute is large (0.1 M) or if the matrix is aromatic, ion recombination via tunneling dominates the anion kinetics, and long lived triplet states are observed to grow in. These results and the effects of other charge scavengers indicate that just a few percent of added aromatic material can dramatically increase the probability of charge recombination in aliphatic media, and that this effect involves decreased charge separation distances. The same effect apparently also occurs in alkane liquids at room temperature.

scholarly journals Review of Multi-Physics Modeling on the Active Magnetic Regenerative Refrigeration

2021 ◽  
Vol 26 (2) ◽  
pp. 47
Author(s):  
Julien Eustache ◽  
Antony Plait ◽  
Frédéric Dubas ◽  
Raynal Glises
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Room Temperature ◽  
State Of The Art ◽  
Vapor Compression ◽  
Crucial Step ◽  
Potential Alternative ◽  
Vapor Compression Refrigeration ◽  
Preliminary Study ◽  
Physics Modeling

Compared to conventional vapor-compression refrigeration systems, magnetic refrigeration is a promising and potential alternative technology. The magnetocaloric effect (MCE) is used to produce heat and cold sources through a magnetocaloric material (MCM). The material is submitted to a magnetic field with active magnetic regenerative refrigeration (AMRR) cycles. Initially, this effect was widely used for cryogenic applications to achieve very low temperatures. However, this technology must be improved to replace vapor-compression devices operating around room temperature. Therefore, over the last 30 years, a lot of studies have been done to obtain more efficient devices. Thus, the modeling is a crucial step to perform a preliminary study and optimization. In this paper, after a large introduction on MCE research, a state-of-the-art of multi-physics modeling on the AMRR cycle modeling is made. To end this paper, a suggestion of innovative and advanced modeling solutions to study magnetocaloric regenerator is described.

scholarly journals Temperature-Dependent Stimulated Emission Cross-Section in Nd3+:YLF Crystal

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 431
Author(s):  
Giorgio Turri ◽  
Scott Webster ◽  
Michael Bass ◽  
Alessandra Toncelli
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Room Temperature ◽  
Radiative Decay ◽  
Emission Cross Section ◽  
Spectroscopic Properties ◽  
Stimulated Emission ◽  
Different Temperatures ◽  
Stimulated Emission Cross Section ◽  
Semi Empirical

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd3+ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of the 4F3/2 multiplet was investigated by measuring the fluorescence lifetime as a function of the sample temperature, and the radiative decay time was derived by extrapolation to 0 K. The stimulated-emission cross-sections of the transitions from the 4F3/2 to the 4I9/2, 4I11/2, and 4I13/2 levels were obtained from the fluorescence spectrum measured at different temperatures, using the Aull–Jenssen technique. The results show consistency with most results previously published at room temperature, extending them over a broader range of temperatures. A semi-empirical formula for the magnitude of the stimulated-emission cross-section as a function of temperature in the 250 K to 350 K temperature range, is presented for the most intense transitions to the 4I11/2 and 4I13/2 levels.

scholarly journals On the measurement of the ratio of the specific heats using small volumes of gas.—The ratios of the specific heat of air and of hydrogen at atmospheric pressure and a temperatures between 20°C. and —183°C

1925 ◽  
Vol 107 (743) ◽  
pp. 510-543 ◽  
Keyword(s):  
Systematic Error ◽  
Low Temperatures ◽  
Room Temperature ◽  
Expansion Chamber ◽  
Small Vessels ◽  
Specific Heats ◽  
Large Expansion ◽  
Before And After ◽  
The One ◽  
Chamber Capacity

Introduction .—In nearly all the previous determinations of the ratio of the specific heats of gases, from measurements of the pressures and temperature before and after an adiabatic expansion, large expansion chambers of fror 50 to 130 litres capacity have been used. Professor Callendar first suggests the use of smaller vessels, and in 1914, Mercer (‘Proc. Phys. Soc.,’ vol. 26 p. 155) made some measurements with several gases, but at room temperature only, using volumes of about 300 and 2000 c. c. respectively. He obtained values which indicated that small vessels could be used, and that, with proper corrections, a considerable degree of accuracy might be obtained. The one other experimenter who has used a small expansion chamber, capacity about 1 litre, is M. C. Shields (‘Phys. Rev.,’ 1917), who measured this ratio for air and for hydrogen at room temperature, about 18° C., and its value for hydroger at — 190° C. The chief advantage gained by the use of large expansion chambers is that no correction, or at the most, a very small one, has to be made for any systematic error due to the size of the containing vessels, but it is clear that, in the determinations of the ratio of the specific heats of gases at low temperatures, the use of small vessels becomes a practical necessity in order that uniform and steady temperature conditions may be obtained. Owing, however, to the presence of a systematic error depending upon the dimensions of the expansion chamber, the magnitude of which had not been definitely settled by experiment, the following work was undertaken with the object of investigating the method more fully, especially with regard to it? applicability to the determination of this ratio at low temperatures.

scholarly journals The behaviour of visual purple at low temperature

1941 ◽  
Vol 179 (977) ◽  
pp. 151-159 ◽  
Keyword(s):  
Aqueous Solution ◽  
Low Temperature ◽  
Low Temperatures ◽  
Room Temperature ◽  
Absorption Curve ◽  
Quantum Yields

Visual purple is soluble and stable in a mixture of glycerol and water (3:1). At room temperature the spectrum of such a solution is identical with that of the aqueous solution. At — 73° C the peak of the absorption curve is higher and narrower than at room temperature, and it is shifted towards longer waves. The product of photodecomposition at — 73° C has a spectrum in ­ dependent of pH and is at low temperatures thermostable and photostable, but at room temperature it decomposes therm ally to indicator yellow. The primary product appears to be identical with transient orange. The quantum yields of the photoreaction at low and at room temperature are of the same order.

Magnetic Properties of Sputtered Fe-O and Co-O Thin Films

1995 ◽  
Vol 403 ◽  
Author(s):  
D. V. Dimitrov ◽  
A. S. Murthy ◽  
G. C. Hadjipanayis ◽  
C. P. SWANN
Keyword(s):  
Grain Size ◽  
Low Temperatures ◽  
Room Temperature ◽  
Oxide Films ◽  
X Ray Diffraction ◽  
Dc Magnetron Sputtering ◽  
Large Shift ◽  
X Ray ◽  
Grain Size And Shape ◽  
Spherical Grains

AbstractFe-O and Co-O films were prepared by DC magnetron sputtering in a mixture of Ar and O2 gases. By varying the oxygen to argon ratio, oxide films with stoichiometry FeO, Fe3O4, α-Fe2O3, CoO and Co3O4 were produced. TEM studies showed that the Fe – oxide films were polycrystalline consisting of small almost spherical grains, about 10 nm in size. Co-O films had different microstructure with grain size and shape dependent on the amount of oxygen. X-ray diffraction studies showed that the grains in Fe-O films were randomly oriented in contrast to Co-O films in which a <111> texture was observed. Pure FeO and α-Fe2O3 films were found to be superparamagnetic at room temperature but strongly ferromagnetic at low temperatures in contrast to the antiferromagnetic nature of bulk samples. A very large shift in the hysteresis loop, about 3800 Oe, was observed in field cooled Co-CoO films indicating the presence of a large unidirectional exchange anisotropy.

scholarly journals Comparison of preservation methods of Atta spp. (Hymenoptera: Formicidae) for RAPD analysis

2000 ◽  
Vol 29 (3) ◽  
pp. 489-496 ◽  
Author(s):  
Alfredo O. R. Carvalho ◽  
Luiz G. E. Vieira
Keyword(s):  
Silica Gel ◽  
Low Temperatures ◽  
Room Temperature ◽  
Rapd Analysis ◽  
Limiting Factors ◽  
Dna Yield ◽  
Remote Locations ◽  
Leaf Cutting ◽  
Storage Methods ◽  
Plot Design

High quality DNA for molecular studies can be easily extracted from fresh specimens. However, live samples are difficult to keep for long periods thus making their preservation a serious problem, specially when they are collected and transported from remote locations. In order to establish an efficient method to preserve Atta spp. (leaf-cutting ants) for RAPD analysis, six different storage methods were examined: 1) -70°C; 2) 95% ethanol at -20°C; 3) 95% ethanol at 4°C; 4) 95% ethanol at room temperature; 5) silica gel at room temperature; and 6) buffer (0.25 M EDTA, 2.5% SDS, 0.5 M Tris-HCl, pH 9.2) at room temperature. DNA was extracted (Cheung et al., 1993 - modified) and examined after 90, 210 and 360 days of storage. Freshly killed specimens were used as control. DNA yield was measured with a minifluorometer. DNA quality was determined by scanning photographs with a densitometer and the integral of the scan was calculated for DNA of size > 9.4 kb. Data were analyzed using a completely randomized split-plot design with four replicates. All methods were efficient to preserve Atta spp. DNA up to 210 days. At 360 days, DNA was degraded only in 95% ethanol at room temperature, which resulted in RAPD profiles with missing bands. Although preservation at low temperatures is recommended for long periods, methods using silica gel and buffer can be considered satisfactory alternatives when refrigeration and transportation are limiting factors.

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