Non-thermal Population Distribution Research Articles

Plasma-parameter dependence of ro-vibrational temperatures for H2 in LHD divertor

We analyzed a thousand visible spectra of Fulcher-α band measured for divertor plasmas in Large Helical Device. With a coronal model and Bayesian inference, the population distribution of hydrogen molecule in the electronic ground state was estimated. The non-thermal population distribution was recovered with a two-temperature model, which has two sets of rotational and vibrational temperatures, as well as their mixture coefficient. The lower rotational temperature significantly changes according to the plasma parameters. Its nearly linear dependence on the electron density was found, which is consistent with previous works. The lower vibrational temperature also shows a small density dependence, as reported by a previous work. On the other hand, the higher rotational and vibrational temperatures as well as the mixture coefficient only show slight changes over the broad range of plasma parameters. These population parameters show a significant correlation; with higher electron density, all the temperatures and the fraction of the higher-temperature component increase simultaneously. This suggests that the electron impact plays an important role to determine the population distribution.

Quantum coherence, many-body correlations, and non-thermal effects for autonomous thermal machines

One of the principal objectives of quantum thermodynamics is to explore quantum effects and their potential beneficial role in thermodynamic tasks like work extraction or refrigeration. So far, even though several papers have already shown that quantum effect could indeed bring quantum advantages, a global and deeper understanding is still lacking. Here, we extend previous models of autonomous machines to include quantum batteries made of arbitrary systems of discrete spectrum. We establish their actual efficiency, which allows us to derive an efficiency upper bound, called maximal achievable efficiency, shown to be always achievable, in contrast with previous upper bounds based only on the Second Law. Such maximal achievable efficiency can be expressed simply in term of the apparent temperature of the quantum battery. This important result appears to be a powerful tool to understand how quantum features like coherence but also many-body correlations and non-thermal population distribution can be harnessed to increase the efficiency of thermal machines.

Ratio of the surface-enhanced anti-Stokes scattering to the surface-enhanced Stokes-Raman scattering for molecules adsorbed on a silver electrode

Surface-enhanced Raman scattering (SERS) from oxazine 720 (oxa), rhodamine 6G (R6G), and pyridine (py) adsorbed on a rough silver surface was observed. The silver electrode was immersed in aqueous solutions permitting control of the potential bias applied to the surface. SERS spectra in the Stokes and anti-Stokes regions were obtained for several applied potentials and two laser excitation energies. Normalized ratios between the anti-Stokes and the Stokes intensities K were calculated from the SERS spectra. The K ratios differed from unity for all the systems investigated. A preferential enhancement of the (surface-enhanced) Stokes scattering was observed for oxa and py. In contrast, the K ratios were higher than unity for R6G, indicating an increase in the anti-Stokes signal. The K ratios measured in this work decreased with the excitation energy and showed a dependence on the energy of the vibrational modes. These results were satisfactorily explained using resonance models, based on the charge-transfer and electromagnetic theories for SERS. No evidence for a SERS-induced nonthermal population distribution among the vibrational states of the adsorbed molecules (vibrational optical pumping) was found. Therefore, we conclude that the main features of the preferential enhancement of the anti-Stokes scattering for an adsorbed molecule on rough silver can be fully understood in the context of current SERS theories.

Observations of Rotationally Resolved C3in Translucent Sight Lines

The rotationally resolved spectrum of the A1Πu ← X1Σ 000-000 transition of C3, centered at 4051.6 Å, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J ≤ 14) in C3 are best fitted by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C2. Just as in the case of C2, higher rotational levels (J > 14) of C3 show increased nonthermal population distributions in clouds that have been determined to have total gas densities below ~500 cm-3.

Ultrafast vibrational energy redistribution within C–H and O–H stretching modes of liquid methanol

An ultrafast IR–Raman technique is used to study fast redistribution of vibrational energy within CH and OH stretching vibrations of liquid methanol. The instantaneous population distribution throughout the entire CH and OH stretch region (2700–3700 cm −1) is probed simultaneously. The fast redistribution produces a nonthermal population distribution within CH and OH stretching excitations. The nonequilibrium CH stretch population occurs because different CH stretching modes have different lifetimes. The nonequilibrium OH stretch population occurs when OH stretching excitations that are pumped by the laser on the red edge of the band undergo spectral diffusion toward the band center.

Electronic transition moment and rotational transition probabilities in CH. II. B 2Σ−–X 2Π system

Vibrational transition probabilities of the B 2Σ−–X 2Π band system of the CH radical, for the bound levels v′=0 and 1, have been measured in an 8 Torr flame using laser-induced fluorescence. These new branching ratio measurements together with Rydberg–Klein–Rees wave functions furnish an empirical electronic transition moment for this system. A quadratic form compares very well with previous ab initio calculations. The model predicts significant variations in lifetime with rotational quantum number. As a consequence, the Einstein emission and absorption coefficients are strongly dependent on rotational quantum number, and are needed for quantitative temperature and nonthermal population distribution determinations.

Dimer vacancies and dimer-vacancy complexes on the Si(100) surface.

Ab initio total-energy calculations are performed using a conjugate-gradients minimization technique to calculate the properties of various dimer vacancies and dimer-vacancy complexes on the Si(100) surface. A dimer vacancy is found to be a much more probable intrinsic defect for this surface than the recently proposed dimer interstitial. Two mechanisms are identified that contribute to the low formation energy and stability of dimer vacancies on the surface: (i) the need to eliminate dangling bonds in the second layer and (ii) the need for atoms to readjust in order to relax the strain. The results of the calculations provide a good quantitative explanation of the major features of scanning-tunnel-microscopy images obtained from the Si(100) surface. These include the abundance of dimer vacancies, the tendency of dimer vacancies to cluster, and the details of the nonthermal population distribution of distinctive vacancy complexes.

Vibrational energy redistribution and relaxation in the photoisomerization of cis-stilbene

Trans-stilbene photoproduces appearing from the photoisomerization of cis-stilbene within 150 fs are observed to be vibrationally hot, but with a nonthermal population distribution. The product electronic spectrum depends on the incident photon energy. Clearly, intramolecular vibrational energy redistribution is not ultrafast.

Spectral hole burning in large molecules probed with 10 fs optical pulses

Optical pulses with a duration of 10 fs are used to investigate dynamic spectral hole burning and the equilibration of an optically induced non-thermal population distribution of large molecules in solution.

Electron-spin resonance of atomic hydrogen and deuterium at low temperatures.

The electron-spin resonance at 9 GHz of a gas of hydrogen and deuterium has been studied at low temperatures. At 4 K the observation of both H and D provides a rough estimate of the adsorption energy of D on solid ${\mathrm{D}}_{2}$ of 55 K. Below 1 K the ESR of H was used to study electronic spin relaxation, which was due primarily to impurities on the walls of the cavity. This impurity relaxation precluded the possibility of observing a nonthermal population distribution among the states of the atom calculated to occur in its absence. No ESR signal from D was detected below 1 K although a flux into the low-temperature cell was measured. If the recombination is assumed to occur on the surface to which D is bound by 2.6 K, the limit on the density implies that the cross-length for surface recombination is very large, on the order of 300 A\r{}. Such a large cross-length would suggest that a pair of D atoms may form a weakly bound two-dimensional dimer on the surface.

Line shape of the non-thermal 6300 Å O( 1D) emission

The line shape of the non-thermal O( 1D) 6300 Å emission is calculated using the two population model of Schmitt, Abreu and Hays ( Planet. Space Sci. 29, 1095, 1981). The calculated line shapes simulate observations made from a space platform at different zenith angles and altitudes. The non-thermal line shapes observed at zenith angles other than the local vertical have been obtained by using the Addition theorem for spherical harmonics of a Legendre polynomial expansion of the non-thermal population distribution function.

Configuration mixing effects on molecular dipole transition moments

The behavior of dipole transition matrix elements between adiabatic eigenstates of diatomic molecules is explored in the region of large configuration mixing. It is demonstrated that the matrix element has a lorentzian shape as a function of internuclear distance. The effect of this shape on the spectrum of LiH is investigated. The strong enhancement of the dipole transition moment in the interaction region is suggested as a source for nonthermal population distributions and laser radiation in alkali diatomics and hydrides.

Initial Distributions of Vibrational and Rotational Populations Predicted by Statistical Model for Two Diatomic Species Split from Four-Atomic Complex

Initial and nonthermal population distributions among the rotational and vibrational levels of the two diatomic species split from a four-atomic collision intermediate have been studied on the basis of the statistical model which ensures that the angular momentum of the whole system is conserved throughout the course of the splitting. A number of curves have been calculated with the aid of an electronic computer, for the initial rotational population distribution (i. r. p. d.) and the initial vibrational population distribution (i. v. p. d.). The i. r. p. d. computed varies considerably, according as the moments of inertia of the diatomic fragments are equal to or different from each other, and the excess energy E possessed by the intermediate is large or small compared with the vibrational quanta of the fragments. On the contrary, the i. v. p. d. computed remains unchanged in most cases, when the vibrational energy is expressed in the unit of E . Some of the population distributions predicted by the stat...