Molecules In Thermal Equilibrium Research Articles

Unraveling a Cavity-Induced Molecular Polarization Mechanism from Collective Vibrational Strong Coupling.

We demonstrate that collective vibrational strong coupling of molecules in thermal equilibrium can give rise to significant local electronic polarizations in the thermodynamic limit. We do so by first showing that the full nonrelativistic Pauli-Fierz problem of an ensemble of strongly coupled molecules in the dilute-gas limit reduces in the cavity Born-Oppenheimer approximation to a cavity-Hartree equation for the electronic structure. Consequently, each individual molecule experiences a self-consistent coupling to the dipoles of all other molecules, which amount to non-negligible values in the thermodynamic limit (large ensembles). Thus, collective vibrational strong coupling can alter individual molecules strongly for localized "hotspots" within the ensemble. Moreover, the discovered cavity-induced polarization pattern possesses a zero net polarization, which resembles a continuous form of a spin glass (or better polarization glass). Our findings suggest that the thorough understanding of polaritonic chemistry, requires a self-consistent treatment of dressed electronic structure, which can give rise to numerous, so far overlooked, physical mechanisms.

Optical processes for middle atmospheric Doppler lidars: Cabannes scattering and laser-induced resonance fluorescence

The problem of light scattering from a monochromatic laser beam by an ensemble of atmospheric atoms or molecules in thermal equilibrium under ambient wind and temperature is revisited with two emphases. First, the essence of and difference between laser Cabannes scattering (CS) and laser-induced resonance fluorescence (LIF), which permit atmospheric temperature and wind measurements, are simply presented. A classical model is shown to yield the same angular distribution in scattered power for both, a factor of two larger Doppler shift for the former (CS), in the backward direction with the same line-of-sight (LOS) wind, and a dramatic 17 order larger backscattering cross section for the latter (LIF). Second, the LIF process is developed from first principles, and we present the relations between absorption cross section, differential scattering cross sections, and LIF emission spectrum for atoms with hyperfine structure. By doing this, we (1) equate the decoherence rate among the mixed excited substates to half of the Einstein coefficient to comply with energy conservation, and (2) present a clear physical insight into the origin of the Hanle effect, whose quantitative evaluation for these atoms requires quantum mechanical treatment. We then derive LIF emission rates for each of the eight and 10 pathways associated with the D1 and D2 transitions, and deduce the temperature and LOS wind dependence in differential backscattering cross sections of atmospheric sodium and potassium atoms. Using these cross sections allows retrieval of atmospheric parameters in the mesopause region (80–110 km in altitude) by a metal resonance lidar.

Sublimation of the endohedral fullerene Er3N@C80

The heat of sublimation of the endohedral metallofullerene Er3N@C80 was measured via Knudsen effusion mass spectrometry. The large molecule consists of a C80 fullerene cage which is stabilized by comprising a complex of three erbium atoms bounded to a nitrogen atom and has a mass of 1475 amu. The mass spectrum at a temperature of 1045 K and the relative intensities of the thermal fractions of Er3N@C80 are provided. We also discuss possible thermal decomposition processes for these particles. By measuring the quantity of evaporated molecules in thermal equilibrium through a quadrupole mass spectrometer in a temperature range between 782 K and 1128 K, a value for the sublimation enthalpy of Hsub = 237 +-7 kJ/mol is obtained from the second law method.

An approximate likelihood of right censoring from Maxwell-Boltzmanndistribution

The Maxwell-Boltzmann distribution is a premier to identify the distribution of speeds of molecules in thermal equilibrium. The shape of this distribution gets wider for higher temperatures and also the peak decreases. Besides, the mean speed is always higher than the most probable speed due to the skewness of the distribution. The most fabulous property is non-analytic cumulative density function. Consequently, censoring based inferences are function of cumulative density function. The aim in this study is to derive the estimating equation of parameters under type-I and type-II censoring of speed of ideal gas molecules. Using the error function approximation procedure the survival function has been approximated and the procedures of estimating parameters and their standard errors under type-I and type-II censoring have been derived. Besides, the simulation studies have been conducted and the validity of the approximation has been provided.

Ab initio statistical mechanics of surface adsorption and desorption. I. H2O on MgO (001) at low coverage

We present a general computational scheme based on molecular dynamics (MD) simulation for calculating the chemical potential of adsorbed molecules in thermal equilibrium on the surface of a material. The scheme is based on the calculation of the mean force in MD simulations in which the height of a chosen molecule above the surface is constrained and subsequent integration of the mean force to obtain the potential of mean force and hence the chemical potential. The scheme is valid at any coverage and temperature, so that in principle it allows the calculation of the chemical potential as a function of coverage and temperature. It avoids all statistical mechanical approximations, except for the use of classical statistical mechanics for the nuclei, and assumes nothing in advance about the adsorption sites. From the chemical potential, the absolute desorption rate of the molecules can be computed, provided that the equilibration rate on the surface is faster than the desorption rate. We apply the theory by ab initio MD simulation to the case of H2O on MgO (001) in the low-coverage limit, using the Perdew-Burke-Ernzerhof (PBE) form of exchange correlation. The calculations yield an ab initio value of the Polanyi-Wigner frequency prefactor, which is more than two orders of magnitude greater than the value of 10(13) s(-1) often assumed in the past. Provisional comparison with experiment suggests that the PBE adsorption energy may be too low, but the extension of the calculations to higher coverages is needed before firm conclusions can be drawn. The possibility of including quantum nuclear effects by using path-integral simulations is noted.

Sensitivity Enhancement in Fluorescence Correlation Spectroscopy of Multiple Species Using Time-Gated Detection

Fluorescence correlation spectroscopy (FCS) is a powerful technique to measure chemical reaction rates and diffusion coefficients of molecules in thermal equilibrium. The capabilities of FCS can be enhanced by measuring the energy, polarization, or delay time between absorption and emission of the collected fluorescence photons in addition to their arrival times. This information can be used to change the relative intensities of multiple fluorescent species in FCS measurements and, thus, the amplitude of the intensity autocorrelation function. Here we demonstrate this strategy using lifetime gating in FCS experiments. Using pulsed laser excitation and laser-synchronized gating in the detection channel, we suppress photons emitted within a certain time interval after excitation. Three applications of the gating technique are presented: suppression of background fluorescence, simplification of FCS reaction studies, and investigation of lifetime heterogeneity of fluorescently labeled biomolecules. The usefulness of this technique for measuring forward and backward rates of protein fluctuations in equilibrium and for distinguishing between static and dynamic heterogeneity makes it a promising tool in the investigation of chemical reactions and conformational fluctuations in biomolecules.

CIDEP of 2-Chloroxanthone in 2-Propanol: Excitation Wavelength Dependence and Effect of Cross Relaxation

The pattern of a chemically induced dynamic electron spin polarization (CIDEP) spectrum of 2-chloroxanthone (2-ClXn) in 2-propanol depends on the excitation wavelength. To clarify the cause of this intriguing phenomenon, we have investigated the details of the CIDEP and the transient visible absorption of 2-ClXn in 2-propanol produced by excitation at 355 or 308 nm. The CIDEP spectrum is strongly temperature dependent, which is mainly due to the temperature dependence of the net polarization. The net polarization consists of a fast rising emissive polarization and a slow rising absorptive polarization, both at 308 and 355 nm. However, the relative contributions of the two polarizations are different depending on the excitation wavelength, with more emissive polarization at 308 nm. From the analyses of the time profiles of the CIDEP signals and the results of quenching experiments with 2,6-di-tert-butylphenol, it is concluded that the emissive polarization arises from the triplet mechanism (TM) due to the reaction of highly excited 2-ClXn and the absorptive polarization arises from a slow reaction of the triplet molecules in thermal equilibrium. When excited at 355 nm the phase of the CIDEP spectrum of the 2-hydroxy-2-propyl radical due to the singlet−triplet mixing radical pair mechanism (ST0M−RPM) is inverted at later times. It is shown by simulation that large inverted signals can be produced by the electron−nuclear cross relaxation mechanism under proper conditions.

Anharmonicity and cross section for absorption of radiation by water dimer

We calculate the absorption cross section of water dimer molecules in thermal equilibrium at temperatures typical of the lower atmosphere using quantum mechanical coupled nonlinear equations of motion. Empirical Morse-oscillator potentials are used to describe the local modes of water monomer, and the RWK2 potential is employed for the interaction between atoms of different water monomers. The strong anharmonicity is taken into account by an extension to molecular dimers of methods originally developed for the lattice dynamics of solid helium. Approximations based on exploiting the hierarchy of energy scales in the dynamics of the weakly hydrogen-bonded water dimer allow the determination of the absorption spectrum over the range of significant solar radiation, up to 20 000 cm−1, including the important contributions of overtone and combination transitions. This approach can tackle the complicated task of mixing of vibrational fundamentals and overtones. We have found that the absorption by these vibrational overtones, within the solar energy range, is quite significant due to the anharmonicity of Morse-oscillator potentials and the large vibrational amplitude of hydrogen atoms. These overtones may play a role in the solar energy absorption of the atmosphere.

State specific velocity distribution of hydrogen isotopes desorbing from Pd(100)

Velocity distributions of recombinatively desorbing hydrogen molecules and their isotopic variants HD and D 2 have been determined with internal state selection using resonantly enhanced (VUV + UV) two-photon ionization spectroscopy. In the experiments the surface temperature of the permeation source is kept constant at various temperatures between 440 and 770 K. The velocity distributions of molecules desorbed from a clean Pd(100) surface are found to be Maxwell-Boltzmann like, but an isotope effect of the average kinetic energy is observed. The kinetic energy of hydrogen molecules agrees with that expected for molecules in thermal equilibrium with the surface. For deuterium molecules the average kinetic energy 〈 E kin〉 is about 10–30 meV higher than expected for molecules in a thermal equilibrium at T s . Within the experimental error bars no significant dependence of the average kinetic energies on the rovibrational states is detected. Preadsorption of sulfur leads to a non-Maxwell-Boltzmann velocity distribution with a significantly enhanced average kinetic energy.

Vibrational activation in associative desorption of hydrogen from Pd(100)

Using resonantly enhanced two-photon ionization, vibrationally excited hydrogen molecules are observed with rotational state selection in associative desorption from a Pd(100) surface. The population in the excited vibrational states of all three stable isotopes is significantly higher than expected for molecules in thermal equilibrium with the surface. Upon changing the surface temperature T s from 325 to 740 K, achieved by employing a permeation source for the hydrogen supply, the vibrational population increases exponentially with T s. A quantum-mechanical approach based on the concept of a reaction-path calculation is applied to this problem. Implications of this model and distinctions from thermal models are discussed.

On the adsorption of polymer solutions on random surfaces: the annealed case

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOn the adsorption of polymer solutions on random surfaces: the annealed caseDavid Andelman and Jean Francois JoannyCite this: Macromolecules 1991, 24, 22, 6040–6042Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://doi.org/10.1021/ma00022a022RIGHTS & PERMISSIONSArticle Views65Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (288 KB) Get e-Alerts Get e-Alerts

Laser spectroscopy of hydrogen desorption from Pd(100)

The recombinative desorption flux of hydrogen molecules from a Pd{100} surface is investigated with rovibrational state selectivity by resonantly enhanced [vacuum ultraviolet (VUV)+ ultraviolet (UV)] two photon ionization. Using a permeation source for the hydrogen supply the surface temperature can be changed from 325 to 740 K. The population in the rotational states is significantly lower than expected for molecules in thermal equilibrium at the respective surface temperatures, whereas the vibrational population is much higher. This vibrational population increases exponentially with Ts. When interpreted as desorption rates into (v‘=1) and plotted versus T−1s, activation energies Ea for vibrational excitation can be derived. For the three isotopes D2, HD, and H2 values for Ea of 234, 282, and 428 meV, respectively, are obtained, being in all three cases lower than the corresponding gas phase energies. The rotational cooling and the vibrational excitation are discussed in the context of current theoretic...

State selective investigation of recombinative D 2 and HD desorption from Pd(100) and Au/Pd(100)

The recombinative desorption of D 2 and HD from a Pd(100) surface is studied with rotational state selectivity by resonantly enhanced (vuv + uv) two photon ionisation spectroscopy. For the rotational degree of freedom a strong cooling effect is observed. The first excited vibrational level ( v″ = 1) is much more populated than expected for molecules in thermal equilibrium with the surface. This population increases strongly with the surface temperature. The activation energy for ( v″ = 1) desorption deduced from a Boltzmann plot is less than the vibrational energy of free D 2 and HD molcules.

Vibrational activation in recombinative hydrogen desorption from Pd 100

In recombinative desorption of hydrogen from clean Pd100 vibrationally excited molecules are observed. The population in the excited states is higher than corresponding to molecules in thermal equilibrium with the surface. This population also increases nearly exponentially with the surface temperature, T S. If the population is converted to desorption rates, an activation energy for vibrational excitation can be derived. These activation energies of 234 meV, 282 meV, and 428 meV for D 2, HD, and H 2, respectively, are in all three cases lower than the corresponding gas phase energies.

THE PHENOMENOLOGICAL ANALYSIS OF HADRONIC MULTIPLICITY DISTRIBUTIONS

The aims of the present paper are limited to a description of theoretical and phenomenological techniques which are, as far as possible, model independent, or at least valid for a class of models. It is the authors' experience that most of the gross measures of particle reaction data (e.g. total cross sections, inclusive distributions, KNO ''plots,'' etc.) do not discriminate among models unless supplemented with more fine grained information, especially correlations of various kinds. In the absence of a quantitative theory for the exclusive matrix elements, from which all else follows, it seems more constructive to work from the outside to the inside. (An especially powerful tool for this is intensity interferometry, much used in the statistical theory of optics but as yet rather undeveloped for the analysis of elementary particle data.) Whenever possible we emphasize the statistical essence of an observable, which can be rather independent of the particular dynamical process. A familiar example is the Maxwellian energy distribution of gas molecules in thermal equilibrium, whose form (as does the validity of hydrodynamic equations for the system) is independent of the detailed force law. This example illustrates both the strength and weakness of the approach.

Laser diagnostic in molecular beams

The output from a stabilized, tunable single-mode laser is split into two beams which cross the molecular beam perpendicularly and at an angle of β to the beam axis. Tuning the laser frequency across the unshifted and Doppler-shifted absorption profile of the molecular transition yileds the velocity distribution of the molecules in the beam for individual quantum states. The internal state distribution among vibrational and rotational levels in the beam can be determined by comparing the fluorescence simultaneously induced in the beam and in a cell with molecules in thermal equilibrium.

A theoretical investigation of radiation mechanisms of insect chemoreception

A theoretical investigation is performed of the hypothesis that certain insect sensory receptors operate by modal radiation mechanisms, i. e. as dielectric waveguide or resonator aerials, at infrared wavelengths, in the process of chemoreception and temperature measure­ment. The basic physical principles, requirements, and limitations of such mechanisms are discussed. The criterion chosen for the detectability of radiation emitted (absorbed) by stimulus molecules is that the increment (decrement) in signal power be greater than that from fluctua­tions in the background power from sky and ground. Thermal equilibrium processes . Mechanisms involving the emission of characteristic wave­lengths of radiation by vibrationally or rotationally excited odorant molecules in thermal equilibrium with their surroundings, or involving the absorption of characteristic wavelengths of background radiation by odorant molecules in the ground state, are analysed. For both emission and absorption mechanisms, required concentrations of odorant molecules are much greater than observed sensitivity thresholds for pheromones and most scents. There are also severe limitations on the discriminatory ability of any singly innervated sensillum. Non-equilibrium processes . Detection of stimulated or spontaneous emission of infrared radiation from low concentrations of odorant molecules released in excited states by a living organism is extremely difficult. Even for wavelengths in the 3 to 4μm atmospheric window the advantages of non-equilibrium processes are cancelled by the effects of collisions and other factors. However, radiation from fires is readily detectable, by day or night, in the 3 to 4μm window. Triggering of acceptors by non-radiative processes, in which specificity is determined principally by infrared spectrum, is theoretically possible and merits further investigation. Thus radiation mechanisms cannot provide a general mechanism of chemoreception, and in particular cannot account for pheromone detection, but might only operate in rare special cases, for which critical experiments are proposed. A theoretical model of operation of the honeybee pit-organs as dielectric resonators has been constructed as an illustrative example for the analysis.

X1. Zwischenmolekularer Übergang von Elektronenanregungsenergie

AbstractThe studies of sensitized fluorescence in gases and liquids arc discussed, and the possibility of detecting an nontrivial transfer of electronic energy considered. The elementary process of excitation transfer between molecules in thermal equilibrium with their environment is quantitatively treated for pure dipole‐dipole coupling and discussed qualitatively for other cases. The theorie of the elementary process is applied to solutions with statistical distributions of molecules. The transfer between like molecules can occur in several steps. Recent research at very low temperatures can be taken as evidence that such processes are important for the fluorescence of foreign molecules in molecular cristals.

Kinetic theory of the mechanism of muscular contraction

Muscle belongs to a class of highly elastic gels typified by rubber. Results of studies of certain properties of gels seem applicable. 1. The change of fluidity with temperature is logarithmic: log φ=A−Q/TT is absolute temperature. The change of the constants with concentration and mastication suggests that rubber contains long filamentous molecules. 2. The change of viscosity with stirring (thixotropy) suggests an equilibrium between chaotic forces of thermal agitation, and local orientating forces in the neighborhood of molecules or particles. Long molecules in thermal equilibrium are never straight. (Principles of maximum mechanical chaos.) 3. Frictional forces at interfaces are greatly influenced by polar molecules.