Showing papers on "Excited state published in 1974"
732 citations
TL;DR: In this article, a general theory of the fine structure observed on the high energy side of the $K$-absorption edge (EXAFS) is presented, which is useful when the excited atom is not too highly ionized and the potential is approximately spherically symmetric.
Abstract: A general theory of the fine structure observed on the high-energy side of the $K$-absorption edge (EXAFS) is presented. The form of the theory presented is useful when the excited atom is not too highly ionized and the potential is approximately spherically symmetric. A critical analysis is made of long-range-order theories of EXAFS and it is shown that the coherent effects of the periodic potential are not the dominant mechanism as assumed previously. The dominant mechanism is the scattering in the vicinity of the absorbing atom, and can most naturally be calculated by considering only the immediate environment surrounding the absorbing atom. Fourier-transforming EXAFS data determines the spatial dependence of a scattering matrix. This scattering matrix is expected to peak at the location of surrounding atoms, locating them, and can give information on the type of surrounding atoms and possibly the surrounding valence electron density. Because the $K$ edges of different atoms are separated, such information can be obtained around each atom type separately, making EXAFS a potentially powerful tool for determining the microscopic structure of condensed matter.
621 citations
01 Jun 1974
TL;DR: In this paper, a technique is described that allows the measurement of integral cross sections for ion-molecule reactions and electron transfer processes in the energy range from typically 0.1 to 20 eV.
Abstract: A technique is described, that allows the measurement of integral cross sections for ion-molecule reactions and electron-transfer processes in the energy range from typically 0.1 to 20 eV (lab). Basically similar to the tandem mass spectrometer method, it uses inhomogeneous oscillatory electric fields for the storage and guidance of the primary ions and for the collection of the secondary ions. By these means a reduction of the number of excited ions in the primary beam and a good definition of the kinetic energy are obtained, together with a collection and detection probability for the secondary ions, that approaches unity for all scattering angles in a broad energy band. Tire ion beam intensity (10 5 to 10 7 ions per second) is only weakly dependent on the kinetic energy down to typically 0.15 eV (lab). The distribution of the collision energies is mainly determined by the thermal motion of the reactant gas in the scattering chamber (T ≈ 300 K). Measurements are reported for the reactions Ar + + D 2 → ArD + + D and Ne + + CO → C + Ne+O.
406 citations
TL;DR: In this article, a semi-empirical potential model of Baylis has been used with some modifications in the calculation of the molecular terms; in particular, a large number of atomic states are included in their calculation, which ensure the stability of the calculated molecular terms.
Abstract: Numerous excited molecular terms for the various alkali‐rare gas atom pairs have been determined. The semiempirical potential model of Baylis has been used with some modifications in the calculation of the molecular terms; in particular, a large number of atomic states are included in our calculation, which ensure the stability of the calculated molecular terms. Our results show that coupling among molecular terms is very important and gives rise to structure in the excited potential energy curves. Comparisons between our results and other theoretical and experimental data are made.
368 citations
TL;DR: In this article, a semi-empirical model based on the observed atomic splittings is given for treatment of spin-orbit coupling effects, and the adiabatic potential curves resulting from diagonalization of the spinorbit interaction were found essential to the understanding of spectroscopic observations.
Abstract: Ab initio configuration‐interaction calculations on ground‐state Ne2, the excited 1,3Σu,g+ and 1,3Πu,g states of Ne2 formed from Ne(3s; 1,3P) and Ne(1S), and the 2Σu,g+ and 2Πu,g states of Ne2+ have been carried out. The dissociation energies of the 1,3Σu+ excited states of Ne2 were found to be considerably smaller than that of the corresponding molecular ion. Potential maxima were found in the attractive interactions of the excited Ne2 molecule. A semiempirical model, based on the observed atomic splittings, is given for treatment of spin‐orbit coupling effects. The adiabatic potential curves resulting from diagonalization of the spin‐orbit interaction were found essential to the understanding of spectroscopic observations. Estimates of the long‐range dispersion interactions are also presented.
343 citations
TL;DR: In this paper, a molecular beam photodissociation study has been made of a number of simple aryl iodides and bromides and the angular distribution of photofragments is characterized by an anisotropy parameter β which was measured for each molecule.
Abstract: A molecular beam photodissociation study has been made of a number of simple aryl iodides and bromides. The angular distribution of photofragments is characterized by an anisotropy parameter β which was measured for each molecule. The values of β depend on the lifetime of the excited state compared to the rotational correlation times of the molecule as well as on the orientation of the transition dipole with respect to the C–X bond. Knowing these orientations we can extract excited state liftimes as follows: methyl iodide, 0.07 picoseconds (psec); iodobenzene, 0.5 psec; α‐iodonaphthalene, 0.9 psec; and 4‐iodobiphenyl, 0.6 psec. It is concluded that methyl iodide directly dissociates but that the aryl compounds predissociate. The analogous aryl bromides have small anisotropy parameters and it is estimated that they live in the excited state perhaps two orders of magnitude longer than the aryl iodides. The data suggest a mechanism for predissociation in which S2 undergoes intersystem crossing to a triplet s...
278 citations
264 citations
TL;DR: In this paper, an analytical analysis of the photoelectron spectra of core electrons and numerical calculations of their overall line shapes are made with the model proposed in our previous paper.
Abstract: Analytic investigations of the photoelectron spectra of core electrons and numerical calculations of their overall line shapes are made with the model proposed in our previous paper. In the final state of the photoemission, an electronic level of the incomplete shell of the excited atom, initially located well above the Fermi energy e F , is assumed to be lowered down to e d due to the core hole left behind. When e d e F , a singular photoemission edge appears at \(\tilde{\varepsilon}_{\text{F}}\), with a weak spectral hump around \(\tilde{\varepsilon}_{d}\). The results are compared qualitatively with experimental data. Finally, some remarks are made on the relationship between the analytic features of the photoelectron and optical absorption spectra.
262 citations
TL;DR: In this article, the decay of a system resulting from the strong coupling (pv≫1) of a radiative state with a coarse manifold of nonradiative levels {l} excited by a coherent excitation was studied.
Abstract: We study the decay of a system resulting from the strong coupling (pv≫1) of a radiative state |s〉 with a coarse manifold of nonradiative levels {l} (``intermediate case'' molecule in the gas phase) excited by a δ‐pulse (coherent) excitation. By the ``effective Hamiltonian'' formalism we show that a necessary consequence of the coherent excitation is a short quasiexponential decay very similar to the decay obtained in the ``statistical limit.'' In the absence of efficient deactivation processes, this decay is followed by a longer one (the ``anomalously long fluorescence'') due to the incoherent decay of the mixed states which result from the s‐l coupling. The form of this longer decay‐ quasiexponential in some well‐defined cases‐is sensitive to the width of the zero order levels: Collision effects are accounted for by a linear dependence of these widths on the gas pressure. The statistical limit is achieved in the case of efficient deactivation processes. This model is compared to a kinetic scheme including a reversible intersystem crossing, and a good correspondence between the two models is obtained, except for some finer details that only appear in the quantum mechanical treatment. Pressure effects on the luminescence lifetimes and yields are discussed.
257 citations
TL;DR: In this paper, a simple improvement on the usual on-shell approximation (which in the single-atom case is part of the Weisskopf-Wigner approximation) yields new solutions for the various probability amplitudes in the form of infinite series involving all the retardation times.
Abstract: The problem considered is that of two identical two-level atoms a fixed distance $r$ apart, one of which is excited at $t=0$. A simple improvement on the usual on-shell approximation (which in the single-atom case is part of the Weisskopf-Wigner approximation) yields new solutions for the various probability amplitudes in the form of infinite series involving all the retardation times $\frac{\mathrm{nr}}{c}$. The truncated solutions involving only the single retardation time $\frac{r}{c}$ are compared with previously published results both when all photon modes are allowed and when only photons propagating along the interatomic axis are allowed. When the retardation times are neglected, the series are summed to give the well-known results of Stephen and others.
255 citations
TL;DR: In this paper, the molecular structure of formamide has been determined by observing the microwave spectra of the 13 C and 18 O species of NH 2 CHO and ND 2 CHO, assuming the planarity of the molecule.
TL;DR: A simple approximation based on asymptotic wavefunctions is used to calculate the splitting ΔV(R c) between the pair of adiabatic potential energy curves that arise from pseudo-crossing of ionic and covalent states of a diatomic molecule at a large internuclear distance R c as discussed by the authors.
Abstract: A simple approximation based on asymptotic wavefunctions is used to calculate the splitting ΔV(R c) between the pair of adiabatic potential energy curves that arise from pseudo-crossing of ionic and covalent states of a diatomic molecule at a large internuclear distance R c. In this approximation, ΔV(R c) is an exponentially decreasing function of R c and otherwise depends only on the ionization potential of the donor atom and the electron affinity and atomic radius of the acceptor atom. Results obtained for the H*(2s, 2p) + H(1s)→H+ + H- interaction are found to agree well with the ΔV(R c) derived from spectroscopic data for the B 1Σu + excited state of H2 and a variational calculation of Kolos and Wolniewicz. Results for the alkali hydride interactions, M + H→M+ + H-, agree well with estimates of ΔV(R c) derived from spectroscopic data for the A 1Σ+ excited states and a variational calculation of Brown and Shull. Results for the alkali halides agree well with photo-dissociation spectra and with collisio...
TL;DR: In this paper, a graphite crystal surface is resolved and shown to be a consequence of inelastic electron-electron scattering in which the dominant process is the population of final states above the vacuum level by electron-hole pair production via screened-Coulombic interaction between the incident primary electrons and the valence electrons in the solid.
Abstract: Fine structure in the energy distribution of secondary electrons "back-scattered" from a graphite crystal surface is resolved and shown to be consequence of inelastic electron-electron scattering in which the dominant process is the population of final states above the vacuum level by electron-hole pair production via screened-Coulombic interaction between the incident primary electrons and the valence electrons in the solid. The scattering theory of Kane is applicable and emphasizes that features due to one-electron density of final states should be resolvable in experimental secondary-electron-emission spectra of crystals. Experimental results are presented, which provide strong support for this view. Previous measurements on graphite have been extended and weak secondary-electron-emission structure, resolved in the second derivative of the energy-distribution spectrum, is reported for kinetic energies, $10\ensuremath{\lesssim}{E}_{\mathrm{kin}}\ensuremath{\lesssim}40$ eV. Maxima are observed at 16.2, 22.2, 29.2, 31.2, 36.2, and 40.7 \ifmmode\pm\else\textpm\fi{} 0.5 eV above the Fermi energy. Details are presented of a first-principles high-energy band-structure calculation of graphite extending over a 80-eV energy range. The observed spectral features correlate closely with final-density-of-states maxima as predicted by the theory.
TL;DR: In this article, the electron transfer reaction within a donor-acceptor, solvent separated ion pair (2A++2D·−) leading to excited singlet, excited triplet, and ground state products is studied within the framework of the theory of nonradiative transitions.
TL;DR: In this paper, the resonance Raman spectra of β-carotene in isopentane solution have been obtained at low temperature, using eight output lines of the argon-ion laser and a line of the heliumcadmium laser.
TL;DR: In this article, the authors measured correlations between like pions in the inclusive processes a + b → π ± + π + + X to study the space-time mechanism of multiple production.
TL;DR: The line profile of the narrow, symmetric 1s line from neon, recorded with the new ESCA instrument with X-ray monochromatization, is analyzed in this paper.
TL;DR: In this paper, a vibrational analysis of the fluorescence spectrum is given, in terms of the kinetic and quantum-mechanical models of radiationless transitions in intermediate-size molecules.
Abstract: Luminescence spectra, fluorescence, and phosphorescence yields were measured for pyrazine excited to six different vibronic levels of the S 1(n,π*) state in pure pyrazine vapor and in gaseous pyrazine‐SF6 mixtures. The vibrational analysis of the fluorescence spectrum is given. As the total gas pressure increases from 10−2 to several torr, the fluorescence yield decreases and reaches a constant pressure‐independent value almost identical with that observed in condensed phases. The amount of this effect depends on the energy of the excited vibronic level. The phosphorescence yield, equal to zero at the low‐pressure limit, increases with gas pressure. The deviation from the Stern‐Volmer law for the fluorescence quenching is explained by the nonexponential decay of the fluorescence, evidenced by direct measurements of the decay curves. The results are discussed in terms of the kinetic and quantum‐mechanical models of radiationless transitions in intermediate‐size molecules.
TL;DR: In this article, the role of spin-orbit and nonadiabatic effects in the reaction of F atoms with H2 is discussed, and the ground and excited FH2 potential energy surfaces and the required interactions between them are computed by the diatomics-in-molecules method.
Abstract: The role of spin‐orbit and nonadiabatic effects in the reaction of F atoms with H2 is discussed, Ground and excited FH2 potential energy surfaces and the required interactions between them are computed by the diatomics‐in‐molecules method. Using an approximate semiclassical procedure, thermal rate constants for reaction and quenching of F(2P1/2) are estimated to be 1.2 and 8.4×10−12 cm3 mol−1 · sec−1, respectively. Since the former is about an order of magnitude smaller than previously reported calculations of the rate constant for reaction of F(2P3/2) with H2, these results predict a substantial difference in reactivity between the 2P3/2 and 2P1/2 fine structure states of atomic fluorine.
TL;DR: The energy dependence of the total ionization cross section, of its associative fraction, and of the electron energy distribution are compared for the two contrasting groups of repulsive and attractive Penning ionizing systems in the thermal collision energy range.
Abstract: A survey of experiments recently done in the field of Penning ionization by electronically excited metastable species is given, and the implication of their results for the basic physical quantities governing the Penning process is discussed. The energy dependence of the total ionization cross section, of its associative fraction, and of the electron energy distribution are compared for the two contrasting groups of repulsive and attractive Penning ionizing systems in the thermal collision energy range. The populations of different electronic, vibrational, and charge states in Penning ions are discussed and compared with populations resulting from photoionization.
TL;DR: In this article, the moments of excited states and transition probabilities between excited states are calculated within the extended theory of finite Fermi systems and the theoretical results are in fair agreement with the experimental values.
TL;DR: In this article, the average discrepancy between theoretical and experimental excitation energies is 0.1 eV and 1.38 eV, respectively, for the nsa1 Rydberg series.
IBM1
TL;DR: In this paper, the configuration-interaction method has been used to calculate the wave functions and energies for the ground state and some selected excited states of the atoms B to Ne, and the calculated total correlation energies range from 95 to 97% of the empirical correlation energy.
Abstract: The configuration-interaction method has been used to calculate the wave functions and energies for the ground state and some selected excited states of the atoms B to Ne. A systematic way of selecting atomic orbital basis and configurations has been developed and is reported in some detail. The calculated total correlation energies range from 95 to 97% of the empirical correlation energy. Calculated term energies of the carbon atom are within 2% of the spectroscopic values. The correlation energies were analyzed in terms of contributions from various classes of configurations, and these contributions were compared with results of previous work. The energy contributions from the class of configurations of triple and higher electron excitations are estimated to be of the order of (3-4)% of the total correlation energy, which is larger than previous estimates of (1-3)% for these atoms.
TL;DR: In this paper, the quenching of excited inert gas atoms by N 2 O, O 3, Cl 2 and CCl 4 was observed from the bound upper states of ArO, KrO and ArCl.
TL;DR: In this paper, effective potentials to replace the Ar core electrons of Fe and Ni were obtained from ab initio ground state wavefunctions of the two core electrons and tested by comparing with SCF calculations for excited states of Fe, Fe +, Fe 2+, Fe 3+, Ni, Ni +, Ni 2+ and Ni 2 +, and the FeH + molecule.
TL;DR: In this paper, thermal energy electron attachment rate constant for CH3CN is shown to be ≤ 1.24×10−14 cm3 sec−1.1. This is consistent with a three body attachment process, with the nature of the third body being important.
Abstract: Thermal electron attachment to nitromethane, methylcyanide, methyliodide, and methylbromide is compared with capture of electrons by these molecules from highly excited Rydberg states of atoms. Data on thermal electron attachment to CH3NO2 are consistent with a three‐body attachment process, with the nature of the third body being important. The thermal energy electron attachment rate constant for CH3CN is ≤1.24×10−14 cm3 sec−1. Some results on dissociative electron attachment and ion pairing processes in CH3NO2, CH3CN, CH3I, and CH3Br are also presented.
TL;DR: In this article, the potential energy surface for the interaction of two rigid HF molecules has been calculated within the ab initio self-consistent field framework, and some preliminary attempts to fit the surface to an analytic form are described.
Abstract: As a prelude to the study of energy transfer in the HF–HF system, the potential energy surface for the interaction of two rigid HF molecules has been calculated within the ab initio self‐consistent‐field framework. An H(4s 1p/2s 1p), F(9s 5p 1d/4s 2p 1d) basis set of contracted Gaussian function was employed. The number of unique points on the surface is greatly reduced by symmetry, and only 294 points were required to give a fairly complete description of the four‐dimensional surface. Parts of the surface are illustrated by a series of contour maps. Some preliminary attempts to fit the surface to an analytic form are described. The equilibrium geometry of (HF)2 is predicted.