共查询到20条相似文献,搜索用时 4 毫秒
1.
The spontaneous radiative dissociations of the discrete vibrational levels of the B1Σ+u electronic states of H2, HD and D2 of the C1Πu electronic state of H2 into the vibrational continuum of the ground X1Σ+g state are calculated as a function of the emission wavelength. The fluorescent spectra of HD in the Lyman system and of H2 in the Werner system resulting from an excitation source uniform in wavelength are predicted. The vibrational radiative lifetimes are tabulated as are the fractions of radiative decays that lead to dissociation. The effects of centrifugal distortion are discussed briefly. An appendix describes a sum rule used to check the numerical accuracy of the calculations. 相似文献
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P. Defrance T. Kereselidze J. Lecointre Z. S. Machavariani 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,64(2-3):303-310
A simple and straightforward calculating scheme is proposed for electron-impact single and multiple ionization of atoms. The method is based on the application of the Hulthén-Kohn dynamical variational principle. An effective charge seen by the scattered electron is determined for a certain type of trial wave functions mathematically in a rigorous way excluding any empirical assumptions. Validity of the elaborated approach is assessed by calculating triply differential cross section (TDCS) for electron-impact ionization of hydrogen. It is shown that, inclusion of the effective charge into the calculation reduces height of a “binary peak” in comparison with the first Born approximation result. The height of a “recoil peak” depends on the sign of the effective charge. The calculated TDCS are compared with the available experimental data and with the results of sophisticated theories and agreement is found. 相似文献
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L. Lammich S. Altevogt H. Buhr H. Kreckel S. Krohn M. Lange D. Strasser R. Repnow M. Grieser R. Schinke Z.-W. Qu H. Zhu D. Schwalm D. Zajfman A. Wolf 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):103-111
The fragmentation of LiH2
- anions after electron
impact was investigated at the heavy-ion storage ring TSR.
The main reaction channel was found to be electron detachment followed by a
breakup into LiH + H.
In the first ms after production of the molecular ions in a cesium
sputtering ion source, additional
contributions were observed in the Li + H2 and Li- + H2 channels,
hinting at an initial population of a short-lived state of the anion.
To gain a better understanding of the mechanisms underlying the observed
behavior of the system, ab initio calculations of relevant potential
energy surfaces were performed at selected geometries.
The experimental findings are discussed in the
light of these calculations. 相似文献
5.
The self-consistent fluid variational model (SFVM) has been used to describe the pressure dissociation of dense hydrogen at high temperatures. This paper focuses on a mixture of hydrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperatures. The equation of state and dissociation degree have been calculated from the free energy functions in the range of temperature 2000-10,000K and density 0.02-1.0g/cm^3, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in higher density range, while temperature dissociation is a more gradual effect. 相似文献
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Farouq Ahmed Ryuji Muira Hideyuki Tsuboi Akira Endou Momoji Kubo 《Applied Surface Science》2010,256(24):7643-10513
Ultra accelerated quantum chemical molecular dynamics method (UA-QCMD) was used to study the dynamics of the hydrogen spillover process on Pt/CeO2 catalyst surface for the first time. The direct observation of dissociative adsorption of hydrogen on Pt/CeO2 catalyst surface as well as the diffusion of dissociative hydrogen from the Pt/CeO2 catalyst surface was simulated. The diffusion of the hydrogen atom in the gas phase explains the high reactivity observed in the hydrogen spillover process. Chemical changes, change of adsorption states and structural changes were investigated. It was observed that parallel adsorption of hydrogen facilitates the dissociative adsorption leading to hydrogen desorption. Impact with perpendicular adsorption of hydrogen causes the molecular adsorption on the surface, which decelerates the hydrogen spillover. The present study also indicates that the CeO2 support has strong interaction with Pt catalyst, which may cause an increase in Pt activity as well as enhancement of the metal catalyst dispersions and hence increasing the rate of hydrogen spillover reaction. 相似文献
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We have obtained improved values for the dissociation energies of molecular hydrogen and its ion by using a high-resolution pulse-amplified laser to probe the second dissociation limit. The onset of the vibrational continuum is observed by state-selective detection of the atomic products of dissociation, and several auxiliary measurements link the results to the ground state. The dissociation energies are accurate to 0.010-0.026 cm(-1), improving previous measurements by a factor of 3-7. Agreement with ab initio calculations is good for H2, D2, and their ions, but not for HD and HD+. 相似文献
8.
R. D. Davies 《Contemporary Physics》2013,54(6):428-446
The emission line for neutral hydrogen at 1420 Mc/s is the only line so far discovered in radioastronomy. Since its mechanism of origin is completely understood, observations of this line provide direct information about conditions in interstellar space such as temperatures, densities and velocities. Extensive investigations of our own Milky Way system have shown clearly that it is a spiral galaxy similar to, but rather smaller than, the great spiral nebula in Andromeda. Our knowledge of the spiral structure of galaxies is far from complete; hydrogen-line measures of high-speed expansions in the centre of the Milky Way system may provide a clue to the understanding of this problem. In addition, determinations of the hydrogen content of different types of galaxy reinforce current theories which suggest that irregular galaxies evolve through the spiral form to elliptical galaxies. 相似文献
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The problem of neutral hydrogen outside a perfectly conducting plane surface is re-examined in an approximation in which the interaction potentials, derived from quantum electrodynamics, take a pure image form and the distance R of the proton from the surface is treated as a parameter rather than a dynamical variable. The numerically evaluated eigenfunctions and eigenvalues vary from the normal hydrogenic form for R → ∞ to a form in which the electron is considerably delocalised with a smaller binding energy. The results are expected to hold only for R > Rc ~ 3 Bohr radii, but the deviations from the hydrogen results are much greater than could be found by perturbation theory. 相似文献
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K. A. Moshkunov V. A. Kurnaev 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(5):625-629
The effect of broadening of the energy spectra of fragments of different hydrogen molecular ions scattered from a tungsten surface has been investigated experimentally and by computer simulation. The experimental results are approximated within the explosive model. The contributions of different mechanisms to the broadening of the energy spectra of scattered fragments are discussed. 相似文献
12.
We explore the possibility to observe hard exclusive three-jet production in early LHC runs, corresponding to diffractive dissociation of the incident proton into three jets with large but compensating transverse momenta. This process is sensitive to the proton unintegrated gluon distribution at small x and to the distribution of the three valence quarks in the proton at small transverse distances. The corresponding cross section is calculated using an approach based on kt factorization. According to our estimates, observation of hard diffractive three-jet production at LHC is feasible for jet transverse momenta q⊥∼5 GeV. 相似文献
13.
In order to produce a supercooled liquid phase of molecular hydrogen that may possibly change at a sufficiently low temperature to a superfluid state, it is suggested to reduce the temperature of its equilibrium coexistence with the solid phase by means of developing different pressures in these phases through the use of linear mechanical pressure on the solid phase or of external electric field. The thermodynamic functions of hydrogen are calculated in both the stable and metastable regions; its phase diagram and the region of possible transition to a superfluid state are also found. The values of excess pressure on the solid phase and of external electric field intensity are estimated, which are necessary for the stabilization of this state. 相似文献
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Brena B Nordlund D Odelius M Ogasawara H Nilsson A Pettersson LG 《Physical review letters》2004,93(14):148302
Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path. 相似文献
16.
The near-threshold highly bound states of all three stable isotopic
variants of molecular hydrogen have been studied. Numerous
perturbations and unexpected transitions are observed as far as
1cm\sj{-1} just below the second dissociation threshold. This
complex structure may arise from a combination of nonadiabatic
coupling between B, B', C electronic states, perturbations due to
fine and hyperfine interactions, and strong shape resonances. The
perturbed near-threshold states and vibrational continuum exhibit
finegrained structure, differing greatly between isotopes because of
varying nonadiabatic coupling. 相似文献
17.
Wolfgang Lotz 《Zeitschrift für Physik A Hadrons and Nuclei》1968,216(3):241-247
Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for all ionization stages from hydrogen to calcium (Z=20). Ionization rate coefficients are given for these species on the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account. 相似文献
18.
A study is presented of adiabatic and non-adiabatic corrections to the dissociation energies and bond lengths of H+ 2, D+ 2 and HD+ in vibration-rotation levels of their ground electronic states, with particular attention to isotopic scaling. In previous work (MOSS, R. E., 1999, Molec. Phys., 97, 1) on rotationless levels, an anomalous non-adiabatic correction to the bond length was found for v = 20, N = 0 of HD+. Other levels close to dissociation are identified that display anomalous non-adiabatic corrections to the dissociation energies and to the bond lengths. The source of these anomalies is discussed. 相似文献
19.
We present a microscopic quantum theoretical analysis of the nanoscale superfluid properties of solvating clusters of para-H2 around the linear OCS molecule. Path-integral calculations with N=17 para-H2 molecules, constituting a full solvation shell, show the appearance of a significant superfluid response to rotation around the molecular axis at T=0.15 K. This low-temperature superfluid response is highly anisotropic and drops sharply as the temperature increases to T approximately 0.3 K. These calculations provide definitive theoretical evidence that an anisotropic superfluid state exists for molecular hydrogen in this microscopic solvation layer. 相似文献
20.
We perform first-principles quantum simulations of dissociation of trapped, spatially inhomogeneous Bose-Einstein condensates of molecular dimers. Specifically, we study spatial pair correlations of atoms produced in dissociation after time of flight. We find that the observable correlations may significantly degrade in systems with spatial inhomogeneity compared to the predictions of idealized uniform models. We show how binning of the signal can enhance the detectable correlations and lead to the violation of the classical Cauchy-Schwartz inequality and relative number squeezing. 相似文献