Inverse Temperature Dependence Research Articles

Temperature dependence of near resonant vibration → vibration energy transfer in HCl–D2 mixtures

Laser-excited vibrational fluorescence measurements have given rates for nearly resonant vibrational energy exchange between HCl and D2 molecules over the temperature range of 196–343°K. The energy transfer cross section σν ν shows an inverse temperature dependence; namely, decreases as temperature increases. The magnitude and temperature dependence of these cross sections could be fit by first order calculations based on quadrupole-quadrupole, and dipole-quadrupole interactions. The rates of vibrational deactivation of HCl by He were found to increase with temperature. However, the results on HCl self-relaxation also show an inverse temperature dependence over this temperature range studied. This enhancement observed at lower temperature is probably caused by the attractive chemical forces exerted between HCl molecules.

Vibration-to-vibration energy transfer via short range forces

The contribution of an exponential and a gaussian short range force to vibration-to-vibration energy exchange is calculated in the impact parameter approximation. For near-resonant conditions, an inverse temperature dependence of the exchange probability is predicted. Estimates of selected exchange probabilities predicted by this theory are made for CoCo, HClHCl and HBrHBr. These results are in all cases greater than the predictions of SSH theory and are close to the experimental values for HCl-HCl and HBr-HBr.

Vinyl acetate emulsion polymerization. I. Effect of ionic strength and temperature on monomer solubility in the ionically stabilized polymer particle

AbstractSolubility of monomer in the polymer was strongly affected by ionic strength; with increasing ionic strength, solubility was found to increase. At constant temperature, this was entirely due to the decrease in interfacial tension, as the condensation of surfactant proceeded at the interface. The temperature affected both the polymer–solvent interaction parameter as well as the interfacial tension. These are the two parameters on which solubility depends. The variations of interfacial tension with temperature was found to be complex, but entirely dependent on the entropic consideration of adsorption. The polymer–solvent interaction parameter–inverse temperature dependence was found to be linear, as expected.

Sensitized fluorescence of diatomic free radicals by Hg(6 3P 0) metastables

Mercury 6 3P 0 metastables were shown to sensitize the emission of a number of diatomic free radicals (HgH, HgCl, CN, OH, and NH) of photochemical interest. Evidence is presented that the energy transfer process is a non-Franck-Condon one at least for HgCl and CN. An inverse rotational temperature dependence on nitrogen pressure was observed for the HgH( 2Π 1 2 ) u′ = 0 state and attributed to near resonant rotational-rotational relaxation processes involving the zeroth and first vibrational levels.

Vibrational relaxation in the HF–HCl,HF–HBr,HF–HI, and HF–DF systems

The laser-excited fluorescence method has been employed to determine rate constants for vibrational energy transfer (V → V, R) and deactivation (V → R, T) processes in the HF–HCl,HF–HBr,HF-HI, and HF–DF systems at temperatures of 300 and 350°K. The rates exhibit a marked inverse temperature dependence indicative of strong attractive (hydrogen-bonding) intermolecular forces. Energy transfer from HF to HI appears to occur by a double vibrational quantum transition in HI.

Magnetic nonequivalences in 2,2,4‐trimethylpentane‐1,3‐diol diisobutyrate and diacetate

Abstract2,2,4‐Trimethylpentane‐1,3‐diol diisobutyrate (1) and diacetate (2) exhibit magnetic nonequivalence for both sets of geminal‐dimethyl groups adjacent to the asymmetric center, and nonequivalence of the methylene protons three bonds removed. Solvent and temperature studies indicate that one geminal‐dimethyl moiety is affected only by intramolecular influences, while the other is also subject to solvent effects. The behavior is rationalized in terms of a preferred conformation in which steric effects prevent the interaction of one moiety with solvent. An inverse temperature dependence for methyl nonequivalence is observed for 2 and an absence of a temperature dependence is noted for 1. The unusually large methylene nonequivalences, 23 Hz in 1 and 34 Hz in 2, are attributed to the proximity of an ester carboxylate.

Plastic Deformation of Al–Li Single Crystals Containing Al<SUB>3</SUB>Li Particles

The effect of the presence of the ordered particles, Al3Li, on plastic deformation was studied at room temperature and at −196°C by using Al–3%Li single crystals. The volume fraction and the size of Al3Li ranged between 0.6 and 22% and 35 and 850Å respectively. Stress-strain curves and slip morphology were investigated. Microstructures of the deformed specimens were also observed by means of transmission electron microscopy. Sharp serrated flow which accompanied the formation of distinct and inhomogeneous slip bands was observed. For all the volume fractions and the sizes of the precipitate particles investigated, the particles were found to be sheared with only a few percent of elongation. The inverse temperature dependence of flow stress which is observed for a single phase alloy with the Ll2 structure was also detected in the crystals with high volume fractions of Al3Li. From its orientation dependence this phenomenon was explained on the basis of the frequency of pinning of dislocations caused by cross slip of a pair of superlattice dislocations into a cube plane. It has been established that the precipitation hardening at sufficiently low temperatures at which the cross slip does not occur can be determined by the resistance induced when a pair of superlattice dislocations cuts through the ordered particles.

De-excitation of CO2(00°1) by Hydrogen Fluorides

Vibrational de-excitation of CO2(00°1) by HF and DF molecules is investigated on the basis of vibration-to-rotation energy transfer in the temperature range 300°–2000°K. The calculation shows that the vibrational relaxation is very fast in both CO2 (00°1) -HF and CO2(00°1)-DF collisions, and the results are in reasonable agreement with laser-excited fluorescence measurements around 350°K. For CO2 (0001) -HF, an inverse temperature dependence of the relaxation time is found between 300° and 400°K; the relaxation time at 360°K is about 30% longer than that at 300°K. For this system the relaxation times change from 0.023 μ sec·atm at 300°K to 0.0035 μsec· atm at 2000°K. No inverse temperature dependence is found for CO2 (0001) -DF. From a comparison with experimental data it is predicted that the deexcited-states of CO2 are (00°0) and (0110), respectively, for the CO2 (0001) -HF and CO2 (0001) -DF relaxation processes. The difference in the final states is explained in terms of the relative efficiency of HF and DF in de-exciting CO2(00°1). Throughout the calculation, the effects of translational motion and molecular attraction on relaxation processes are considered.

Temperature profile and thermal-spreading resistance for a semi-infinite type-IIa-diamond heat sink

The steady-state temperature profile and thermal-spreading resistance for a uniform heat source on a semi-infinite type IIa-diamond heat sink are calculated. The inverse temperature dependence of the diamond thermal conductivity is taken into account.

Distributions of Nighttime F‐Region Molecular Ion Concentrations and 6300‐Å Nightglow Morphology

A numerical technique is employed in solving the coupled, nonlinear system of equations for the O+, NO+, and O2+ number densities in the nighttime F region, including the effects of diffusion, E×B drift, and neutral air motions. The best fits to the ‘sunset’ [Johnson, 1967] and ‘midnight’ [Holmes et al., 1965] rocket observations of the ion profiles obtained at White Sands, New Mexico, are achieved by iteratively varying the neutral wind, the electrodynamic drift, the neutral atomic nitrogen and nitric oxide concentrations, and the ion‐atom interchange and dissociative recombination rate coefficients. The best fit results for both sets of profiles with a Jacchia model atmosphere are achieved with the rate coefficients (cm3 sec−1) at 300°K given by γN2 = 1.1×10−12, γO2 = 2.0×10−11, αNO+ = 3.5×10−7, and αO2+ = 3.1×10−7, each with an assumed inverse temperature dependence. In addition, the ‘sunset’ best fit solutions require that the chemical time constant τ for reaction of O2+ with N and NO be 500 seconds at 200 km and that the net vertical plasma transport velocity wz due to E×B drift and a neutral wind be downward with a speed of 14 m sec−1. The midnight best fit solutions are achieved with τ = 2.5×103 at 200 km and wz = 10 m sec−1 upward. The 6300‐Å nightglow morphology in the inter‐tropical region is computed directly from the ion concentrations calculated for assumed drift and neutral wind models representative of equinoctial, sunspot‐minimum conditions. Isophote contours of zenith intensity are presented to illustrate the nightglow morphology associated with the decay of the Appleton anomaly. Calculated results are compared with the observations of Barbier [1964] to demonstrate the influence of electrodynamic drift on the morphology of nightglow enhancements. The results show that the electrodynamic drifts required to produce the observed enhancements are consistent with the drifts observed at Jicamarca.

Temperature Dependence of the Three-Body Recombination Coefficient in a Highly Ionized Potassium Plasma

Measurements of the volume recombination coefficient of a highly ionized potassium plasma demonstrate the strong inverse temperature dependence predicted theoretically, and provide further confirmation of the three-body nature of the recombination process.

Al-Mg合金における降伏応力の逆温度依存性

Al-Mg合金における降伏応力の逆温度依存性

Radiolysis of binary mixtures. Part II. The effect of irradiation temperature on the radiolysis yields of methanol in benzene

The effect of irradiation temperature on the yields of radiolysis and scavenging products from methanol and methanol–benzene solutions has been examined over the temperature range + 110° to –196°. The temperature-dependence of the yield of the radiolysis products is generally small. The results have been examined in terms of current theories of radiation chemistry including the hot-species model and the thermal-spike concept. The yields of the scavenging products cyclohexa-1,4-diene, anisole, and phenylcyclohexadiene display an inverse temperature-dependence, while the yield of cyclohexadienylmethanol displays a complex temperature-dependence. The results, particularly for the hydrogen and cyclohexa-1,4-diene yields, appear to demonstrate a direct relationship between the decrease in hydrogen yield and yield of cyclohexa-1,4-diene from methanol containing any initial benzene concentration.

Resonance Absorption of p-Benzosemiquinone in the Zeeman Region

The resonance absorption of p-benzosemiquinone in sodium ethylate—ethanol solution has been determined from t=−50°C to room temperature in the Zeeman region at frequencies of the order of the zero field splitting produced by the isotropic hyperfine coupling. At t=−50°C, the resonance absorption indicated free-radical interactions with two sodium nuclei. The isotropic coupling constants measured for the free electron spin—1H and 23Na interactions were, respectively, | A | = 6.63±0.01 MHz and | A′| = 0.34±0.05 MHz. Due to the finite widths, resonance absorptions were observed near Hz = 0 for rf frequencies of ν/ | A | = 2.48±0.01 and 1.49±0.01. The observed linewidth inverse temperature dependence for −20°≤t≤0°C was explained on the basis of the over-all chemical exchange process[Complex chemical formula],whence the first-order rate of disappearance chemical exchange time τe,k=|A′|−1×exp[Ea(T−1−T0−1)/R] was obtained. The over-all energy of activation was determined to be Ea = 10±1 kcal mole−1 and T0 = 253°±5°K. Also, since the solvent—free-radical interactions occur at the end oxygen atoms, an estimate was made of the role played by the spin—orbit—lattice interactions introduced in the p-benzosemiquinone ion by the asymmetric vibration of the CO bonds. In the Zeeman region, the transition probability per unit time between a participating pair of levels induced by Van Vleck second-order Raman processes was estimated to be of the same order of magnitude, W∼104 sec−1, as other processes considered previously for p-benzosemiquinone in solution. This is however two orders of magnitude less than the experimental values.

Nuclear Paramagnetism of Helium-3—Helium-4 Solutions above 0.9°K

The temperature dependence of the nuclear susceptibility of pure ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{3}$-${\mathrm{He}}^{4}$ mixtures of ${\mathrm{He}}^{3}$ concentrations 0.81, 0.70, 0.38, and 0.14 has been determined with an accuracy of \ifmmode\pm\else\textpm\fi{}1% for $0.92<T<2.9$\ifmmode^\circ\else\textdegree\fi{}K. This work is an extension of that of Fairbank, Ard, and Walters, and shows that within experimental error the temperature dependence for the solutions is the same as that of the pure liquid. The maximum deviation of the susceptibilities from an inverse temperature dependence is approximately 5%. These results indicate that the susceptibility is insensitive to the average separation of the ${\mathrm{He}}^{3}$ atoms, contrary to the behavior that might be expected from a Fermi system in which exchange is important. A perturbation calculation, however, suggests that such behavior can be understood as a near cancellation of terms arising from the exclusion principle and the exchange interaction.

LAG PERIOD CHARACTERIZING THE ENTRY OF TRANSFORMING DEOXYRIBONUCLEIC ACID INTO BACILLUS SUBTILIS.

Levine, James S. (Yale University, New Haven, Conn.), and Norman Strauss. Lag period characterizing the entry of transforming deoxyribonucleic acid into Bacillus subtilis. J. Bacteriol. 89:281-287. 1965.-The kinetics of appearance of transformants as a function of time of exposure to deoxyribonucleic acid (DNA) has been studied in Bacillus subtilis. A short lag period of approximately 1 min at 37 C is evident when the transformation is terminated with deoxyribonuclease. The length of this lag is independent of the genetic trait transferred. Moreover, the lag is unaffected by transforming DNA concentration, by the presence of homologous unmarked DNA, and by shearing and cross-linking of the transforming DNA. The lag shows a strong inverse temperature dependence. The energy of activation is 13.9 kcal. The lag is abolished when the transformation is terminated by washing instead of by addition of deoxyribonuclease. These results are taken to indicate an immediate adsorption of DNA to cells, followed by a deoxyribonuclease-sensitive period of 1 min, during which time the genetic trait is entering the cell. These results make feasible an investigation of the configuration assumed by the DNA molecule during entry into the cell.

Rare Earths in Covalent Semiconductors: the Thulium-Gallium Arsenide System

Solutions containing radioactive 170Tm were applied to the surface of GaAs wafers that were heated to 800°, 900°, or 1000°C for times up to 100 h. The solubilities and diffusion coefficients were obtained by fitting the experimental data with complementary error functions. The resulting surface concentration (cm−3) was taken as the equilibrium saturation solubility and is represented below the eutectic temperature of 1150°C by 6.7×1025 exp (−2.3 eV/kT), which gives Cmax=4×1017 cm−3. The atom size, defined as the single-bond radius, was found to be the dominant factor in limiting the solid-solution solubility of the rare earths in GaAs. Diffusion was faster at lower temperatures, and the diffusion coefficient D (cm2/sec) was 2.3×10−16 exp (1.0 eV/kT). This inverse temperature dependence of the diffusion coefficient may be explained by the effective D derived from the concept of simultaneous diffusion and chemical reaction. The resulting diffusion coefficient in intrinsic material is Dei=DiCii+/Cs0, where Di is the interstitial diffusion coefficient and Cii+/Cs0 is the ratio of singly ionized interstitial concentration to neutral substitutional concentration. The inverse temperature dependence of D may be ascribed to the more rapid increase of Cs0 with temperature than that of DiCii+.

Magnetization of Localized States in Metals

A study has been made of the magnetic properties of dilute solutions of iron in various nonmagnetic 4d series elements and alloys. In some cases the iron atoms possess a localized magnetic moment which manifests itself as an inverse temperature dependence in the susceptibility of the solution. The occurrence of the moment is determined by the valence electron concentration in the solute element (or alloy). As a function of this quantity one finds portions of the 4d series in which localized moments are strictly absent, interspersed by regions—one centered near Mo, the other in the vicinity of Rh and Pd—in which magnetization occurs and at whose edges the moments appear almost discontinuously. This behavior may be understood in terms of a theoretical model in which the magnetization is ascribed to a virtual level, of the type proposed by Friedel, of the iron atom. Polarization occurs when the virtual level lies near the Fermi level and is sufficiently sharp in energy. A self-consistent Hartree-Fock calculation indicates that under these circumstances the impurity atom develops an exchange potential which splits the level—causing it to have different energies for spin-up and spin-down electrons and thus giving rise to magnetization. The model gives a qualitative description of the experiments and, in particular, is able to account for the fact that the impurity atoms sometimes carry a moment that is a fraction of a Bohr magneton.

Electron Paramagnetic Resonance ofFe3+in TiO2(Rutile)

Paramagnetic resonance has been observed from 2 kMc/sec to 110 kMc/sec in ${\mathrm{Fe}}^{3+}$-doped single crystals of rutile at 78\ifmmode^\circ\else\textdegree\fi{}K, 4.2\ifmmode^\circ\else\textdegree\fi{}K, and 1.4\ifmmode^\circ\else\textdegree\fi{}K. The rather large zero field splittings measured between the three doublets are 43.3\ifmmode\pm\else\textpm\fi{}0.1 kMc/sec and 81.3\ifmmode\pm\else\textpm\fi{}0.1 kMc/sec. The derived constants for the spin Hamiltonian ${\mathcal{H}=g\ensuremath{\beta}\mathrm{H}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{S}\ifmmode\times\else\texttimes\fi{}D({{S}_{z}}^{2}\ensuremath{-}\frac{35}{12})+E({{S}_{x}}^{2}\ensuremath{-}{{S}_{y}}^{2})+(\frac{a}{6})({{S}_{x}}^{4}+{{S}_{y}}^{4}+{{S}_{z}}^{4}\ensuremath{-},\frac{707}{16)}}{+(\frac{7}{36})F[{{S}_{z}}^{4}\ensuremath{-}(\frac{95}{14}){{S}_{z}}^{2}+\frac{81}{16}].}$ are $D=20.35\ifmmode\pm\else\textpm\fi{}0.1$ kMc/sec, $E=2.21\ifmmode\pm\else\textpm\fi{}0.07$ kMc/sec, $a=1.1\ifmmode\pm\else\textpm\fi{}0.2$ kMc/sec, $F=\ensuremath{-}0.5\ifmmode\pm\else\textpm\fi{}0.3$ kMc/sec, $D=20.35\ifmmode\pm\else\textpm\fi{}0.1$ kMc/sec, $E=2.21\ifmmode\pm\else\textpm\fi{}0.07$ kMc/sec, $a=1.1\ifmmode\pm\else\textpm\fi{}0.2$ kMc/sec, $F=\ensuremath{-}0.5\ifmmode\pm\else\textpm\fi{}0.3$ kMc/sec, $g=2.000\ifmmode\pm\else\textpm\fi{}0.005$. The average line width is 35 Mc/sec for 2\ifmmode\times\else\texttimes\fi{}${10}^{19}$ spins per ${\mathrm{cm}}^{3}$, and the average spin-lattice relaxation time ${T}_{1}$ at $T=1.4\ifmmode^\circ\else\textdegree\fi{}$K is 4 msec. ${T}_{1}$ still has a very slow inverse temperature dependence even at $T=78\ifmmode^\circ\else\textdegree\fi{}$K. An increase in sensitivity over metal walled cavity spectrometers was achieved by using the pieces of Fe-doped rutile as the microwave resonators.

Viscosity and Density of the Liquid System TNT-Picric Acid and Four Related Pure Materials

The viscosity and density of the system TNT-picric acid and four related substances have been investigated over a range of temperature which included both normal and supercooled liquids. The temperature-dependence of viscosity was found to be best represented by a continuous exponential function of the type η=A exp (B/T+C/T2), which yielded a good fit to the data even well into the supercooled region. Density in each case was found to vary linearly with temperature across the entire range. The results are interpreted as arising from an inverse temperature dependence of the flow activation energy, ΔEvis. It is suggested that ΔEvis may drop to zero at sufficiently high temperature and pressure.