Binding Energy Of Molecule Research Articles

Ultracold ground-state molecule production in sodium

We have observed the formation of ground-state ${\mathrm{Na}}_{2}$ molecules via the spontaneous decay of excited molecules created by the photoassociation of ultracold atoms. We measure the binding energies of molecules created in three hyperfine components of the lowest singlet and triplet potentials of ${\mathrm{Na}}_{2}$ by two different methods. Two of the features are purely triplet a ${}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ $(v=15)$ (quasibound) states that have not been previously observed, while the third is a mixed X ${}^{1}{\ensuremath{\Sigma}}_{g}^{+}--a$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state. The molecules are detected with high-resolution cw laser ionization techniques and binding energies are measured to within 10 MHz.

Spectral theory of the chemical bond

New theoretical methods are reported for obtaining the binding energies of molecules and other atomic aggregates employing the spectral eigenstates and related properties of the constituent atoms in the absence of prior wave function antisymmetry. Calculations of the lowest-lying attractive and repulsive states of the electron pair bond as functions of atomic separation from chemical (exchange) to physical (van der Waals) binding regions illustrate the nature of the formalism and its convergence to values in accord with results obtained employing conventional methods.

Influence of substitution of P by As on exciton and biexciton states in Zn(P 1− xAs x) 2 crystals

Low-temperature (1.8 K) excitonic absorption, reflection and photoluminescence spectra of mixed Zn(P 1− x As x ) 2 crystals have been studied at x=0.01, 0.02, 0.03 and 0.05. Energy gap and rydbergs of excitonic B, C and A-series decrease monotonically with the increase of x. Spectral half-widths of absorption n=1 lines of B and A-series increase monotonically with the increase of x due to fluctuations of crystal potential. Emission lines of excitonic molecules have been observed in photoluminescence spectra of Zn(P 1− x As x ) 2 crystals. Binding energy of molecule increases with the increase of x due to the decrease of the electron-hole mass ratio.

A Road Map for the Calculation of Molecular Binding Energies

During the past decade dramatic progress has been made in calculating the binding energies of molecules. This is the result of two advances reported in 1989: an accurate method for solving the electronic Schrodinger equation that is applicable to a broad range of moleculesthe CCSD(T) methodand families of basis sets that systematically converge to the complete basis set limitthe correlation consistent basis sets. The former provides unprecedented accuracy for the prediction of a broad range of molecular properties, including molecular binding energies. The latter provides a means to systematically approach the complete basis set limit, i.e., the exact solutions of approximations to the Schrodinger equation. These two advances combined with a thorough analysis of the errors involved in electronic structure calculations lead to clear guidelines for ab initio calculations of binding energies, ranging from the strong bonds derived from chemical interactions to the extremely weak binding due to dispersion int...

IMPLICATE FINAL CAUSES IN DEVELOPING MATERIAL SYSTEMS

Causality in changing natural systems can be seen to involve all four Aristotelian causal categories—material, efficient, formal and final. Final causality of materialistic origin can be found in the need to maintain energy flow continuity within dissipative systems. Each interacting dissipative system acts finalistically so as to attract needed energy. In so acting, it continually disturbs its neighborhood by generating potential energy flow disruptions as results of its activities. Final causality based, in this way, on the energy requirements of dissipative systems will generate formal causes as well. In contrast, the emergence of formal causes in mechanistic systems driven solely by efficient causes is extremely unlikely. We suggest viewing the subordination of phenotypic dissipative systems by genotypic counterparts as an historical example of the emergence of formal causes out of the material necessity of maintaining flow continuity. Functional separation between genotypic and phenotypic dissipative systems can occur if the energies to be dissipated are localized, as is the chemical binding energy of molecules with respect to biological functions at a higher scalar level.

Binding Energies of Protonated Betaine Complexes: A Probe of Zwitterion Structure in the Gas Phase

The dissociation kinetics of proton-bound dimers of betaine with molecules of comparable gas-phase basicity were investigated using blackbody infrared radiative dissociation (BIRD). Threshold dissociation energies were obtained from these data using master equation modeling. For bases that have comparable or higher gas-phase basicity, the binding energy of the protonated base.betaine complex is approximately 1.4 eV. For molecules that are approximately 2 kcal/mol or more less basic, the dissociation energy of the complexes is approximately 1.2 eV. The higher binding energy of the former is attributed to an ion-zwitterion structure which has a much larger ion-dipole interaction. The lower binding energy for molecules that are approximately 2 kcal/mol or more less basic indicates that an ion-molecule structure is more favored. Semiempirical calculations at both the AM1 and PM3 levels indicate the most stable ion-molecule structure is one in which the base interacts with the charged quaternary ammonium end of betaine. These results indicate that the measurement of binding energies of neutral molecules to biological ions could provide a useful probe for the presence of zwitterions and salt bridges in the gas phase. From the BIRD data, the gas-phase basicity of betaine obtained from the kinetic method is found to be 239.2 +/- 1.0 kcal/mol. This value is in excellent agreement with the value of 239.3 kcal/mol (298 K) from ab initio calculations at the MP2/6-31+g** level. The measured value is slightly higher than those reported previously. This difference is attributed to entropy effects. The lower ion internal energy and longer time frame of BIRD experiments should provide values closer to those at standard temperature.

Binding energy and oscillator strength of excitonic molecules in type-II quantum wells

The binding energy and oscillator strength of excitonic molecules in type-II quantum wells are theoretically investigated by a variational method with the effective-mass approximation. We have studied two cases for an arrangement of electrons and holes in an excitonic molecule: One is that two holes in the molecule are confined within the same well, adjoined to the well for two electrons; the other is that each hole is confined within different wells, which sandwich the well for two electrons. We found that (i) the binding energy of the molecule depends on the electron-hole mass ratio and well widths, (ii) the bound state of the molecules exists for the limiting range of the well width, and (iii) in the case where each hole in the molecule is confined within a different well the binding energy of the molecule for the heavy-hole limit amounts to 10--30 % of the exciton binding energy for the well width comparable to the exciton Bohr radius. From consideration of the oscillator strength, it is found that, with appropriate parameters, the processes due to both the optical conversion of an exciton into an excitonic molecule and the molecule formation by a two-photon absorption have a similar order of magnitude for an absorption coefficient to that in the single exciton formation. A comparison with the experiment is also briefly discussed.

A DFT-based procedure for predicting core-electron binding energies of chemisorbed molecules using small cluster models: first tests on CO on Ni(100), Pd(100) and Pd(110)

A new method is proposed for the accurate prediction of core-electron binding energies of molecules chemisorbed on metallic clusters as models for metallic surfaces. It involves a formal two-step path in which only the excitation energy from the desired core-level to the conduction band of the cluster is calculated via DFT, the remainder being replaced by the experimental work function of the crystallographic face. Using CO adsorbed on small ( n = 1–4) Ni n and Pd n clusters as examples, the computed C1s and O1s energies show an average absolute deviation of only 0.55 eV, i.e. about three times lower that with direct ΔSCF calculations which actually involve a core-ionized species.

Molecular adsorption to metal particles by applying the image charge method to CO, NH 3 and pyridine

The image charge method is generalized to include the interactions of any given multipole expanded charge distribution with an ideally conducting sphere. Multipole expanded molecular charge distributions obtained at the Hartree-Fock level of theory are employed to address the changes in bindings of CO and NH 3 with radius of the sphere. Results imply the binding energies of molecules to neutral metal clusters to be significantly smaller than to metal surfaces, and a non-monotonic radius dependency is observed for interactions with charged spheres. Analogies in the bindings of NH 3 and pyridine to infinite surfaces are also discussed.

The atomic structure of transition metal clusters

Chemical reactions are used to probe the atomic (geometrical) structure of isolated clusters of transition metal atoms. The number of adsorbate molecules that saturate a cluster, and/or the binding energy of molecules to cluster surfaces, are determined as a function of cluster size. Systematics in these properties often make it possible to propose geometrical structures consistent with the experimental observations. We will describe how studies of the reactions of cobalt and nickel clusters with ammonia, water, and nitrogen provide important and otherwise unavailable structural information. Specifically, small (less than 20 atoms) clusters of cobalt and nickel atoms often adopt entirely different structures, the former having packing characteristic of the bulk and the latter having pentagonal symmetry. These observations provide important input for model potentials that attempt to describe the local properties of transition metals. In particular, they point out the importance of a proper treatment of d-orbital binding in these systems, since cobalt and nickel differ so little in their d-orbital occupancy.

Thin film growth and the scattering of atoms from surface island defects

We investigate the potential energy surface and dynamics of atoms impinging upon pyramidal defects on fcc (100) and (111) surfaces. Illustrative molecular dynamics trajectory results are used to highlight the subtleties of the growth processes. Homoatomic systems of both Cu and Pd are considered in order to determine the influence of extreme differences in bonding coordination variation, i.e. the binding energy per atom decreases by a factor of 3.3 from Cu(bulk) to Cu 2 but more dramatically by a factor of 7.5 for Pd(bulk) to Pd 2. We find that stable adsorption sites on pyramidal facets only exist for three layer high (and higher) facets, but even these sites are not as energetically favorable as those at the pyramid's base. This single energetic effect can promote a Stranski-Krastanov type growth pattern, with a critical roughness of no less than three layers being required before a 3D growth mechanism can propagate in a surface temperature regime where post impact diffusion is small compared to the deposition rate. The transition to 3D growth at the minimum possible roughness would be found for Pd on the (100) face where sticking to the sides of even the three layer pyramid is a high probability event, at a low enough temperature to make post-impact diffusion negligible. However, for the Cu system, we find that the “downward funneling” mechanism smoothed the growth for the three layer pyramid and is still important for the five layer pyramid, indicating that Cu will exhibit layer-by-layer like growth even past three layers. A comparison of scattering simulations from defects show that the growth mode is diffusion limited on the fcc (100) crystal face, but becomes dominated by impact induced disruption of the original structure for a (111) surface. This implies that the (111) surface will grow more smoothly as a new atom displaces pre-adsorbed atoms more easily, an effect that is not included in the “downward funneling” model. The ratio of the diatomic molecule's binding energy to the bulk cohesive energy is shown to provide good insight into the preferred growth mechanism. As the ratio increases, at least in the range spanned by typical metals, the film grows more layer-by-layer like on the (100) surface and less layer-by-layer like on the (111) surface. On the (100) surface, stronger low coordination bonding makes the defect structures less able to adsorb the impacting atom on the sloped faces, increasing the effectiveness of “downward funneling.” On the (111) surface, stronger low coordination bonding inhibits impact disruption of the defects, decreasing this important smoothing mechanism.

Clusters with close packing

An analysis is given of the properties of a cluster cut from a face-centered and a body-centered cubic lattice and also from a hexagonal crystalline lattice about a certain center. The clusters have a shell structure and contain tens and hundreds of molecules. The binding energies of molecules and the surface energy of the cluster are shown for different occupation numbers and for three types of structure of the cluster, and also for different temperatures. It is shown that the concept of surface tension is valid for clusters containing tens of molecules, but from the point of view of the binding energy of the surface molecules a cluster consisting of hundreds of molecules is not a macroscopic particle even at relatively high temperatures. An expression is obtained for the surface energy of a cluster.

The electronic structure of the elements from gas-phase X-ray photoelectron spectroscopy

Abstract This work deals with some recent developments in the study of atoms and molecules by X-ray photoelectron spectroscopy. The experimental techniques of high temperature measurement are discussed, followed by a treatment of core binding energies and the various contributions to their values, in particular relaxation, correlation and relativistic effects. Binding energies in both free atoms and free ions are discussed and compared with corresponding binding energies in molecules and solids. In addition to the ‘main’ peaks observed in photoelectron spectroscopy corresponding to ionization of electrons from various orbitals, weaker satellite structures are also observed, resulting from electron excitation accompanying core ionization. Comparison is made between the intensities of these satellites in various atomic core regions, as well as in molecules containing these atoms. Finally, the photoionization cross-section is shown to change dramatically with the change in the energy of the exciting photon; this appears to have diagnostic value in determining molecular orbital parentage. On the other hand, changes in the photoelectron intensity ratios of spin-orbit components with photon energy may be more subtle, but make possible a very rigorous test of theory.

An extension of the fenske-hall LCAO method for approximate calculations of inner-shell binding energies of molecules

The approximate LCAO MO method of Fenske and Hall has been extended to an all-election method allowing the calculation of inner-shell binding energies of molecules and their chemical shifts. Preliminary results are given.

Polariton Effects in the Optical Spectra of Excitonic Molecules

AbstractStarting from a model Hamiltonian which describes an excitonic molecule‐excitonphoton system at not too high electron‐hole pair densities, an excitonic molecule‐polariton interaction is derived. By means of this interaction the influence of polariton effects on the optical emission, absorption, and scattering processes involving excitonic molecules is studied theoretically. It is shown, that the transition probabilities of these processes are diminished due to polariton effects, especially in substances with small molecule binding energies. Furthermore, some characteristic modifications of the optical spectra (additional lines, changes in the line positions and shapes) are reported.

Exciton Interaction in Photoluminescence from ZnO

AbstractThe luminescence spectra of ZnO platelets at 1.9 K have been investigated under 3371 Å Insor excitation from 5 to 500 kW/cm2. New details in the P‐band luminescence (exciton‐exciton scattering) reveal the separation between A and B excitons in ZnO and the stimulated emission in this band is found to be strong for exciton scattering to higher excited states (n > 2). At the highest excitation powers a new emission line is observed which is associated with the decay of excitonic molecules. The molecule binding energy is estimated to be 15 to 20 meV.

Radiation from Free Excitonic Molecules in CdS Single Crystals

AbstractThe emission and transmission spectra of extremely thin high‐quality CdS single crystals are investigated from 1.8 to 77 °K. At low temperatures using stationary excitation by a high‐pressure mercury lamp an emission spectrum with a pronounced peak 3.2 meV below the energy of the A‐exciton is observed, which is characteristic of all thin crystals investigated. The experimental facts, including kinetic phenomena, suggest an explanation of the emission in terms of a system of interacting excitonic molecules. The molecule binding energy is found to be 3.2 meV.

Estimation of binding energies of molecules by a semiempirical molecular orbital electron correlation method with applications to saturated and unsaturated hydrocarbons, aromatics, and heterocyclics

Estimation of binding energies of molecules by a semiempirical molecular orbital electron correlation method with applications to saturated and unsaturated hydrocarbons, aromatics, and heterocyclics

Ab initio molecular orbital calculations of ESCA chemical shifts using the equivalent cores method

Shifts in molecular core binding energies for molecules containing carbon, nitrogen, oxygen and sulphur are calculated using the equivalent cores method, the heats of reaction being obtained from minimal Slater basis set calculations. The shifts obtained are compared with those obtained from orbital energy differences.

Absorptive Part of Charge Polarization Corrections for Electron Scattering in the Kiloelectron Volt Energy Range

The calculation of the effect of the absorptive part of charge polarization on elastic electron scattering is investigated in the second Born approximation using closure in an approximate manner. Errors in a previous study are corrected, and the angular dependence of the polarization correction is found to be strongly peaked in the forward direction with a long tail at large s values which makes a significant contribution to the scattering. The effects of the polarization correction on the scattered intensity and on the phase of the scattered amplitude are discussed in view of experimental observations. Results for the case of elastic electron scattering from Xe are found to be in good agreement with experiment. Corrections to the diffraction measurement of chemical binding energies of molecules containing first-row elements appear to be negligible.