Lyman-α excitation spectra in the photodissociation of the doubly excited states of H2

A Lyman-α excitation spectrum has been observed using synchrotron radiation in the energy region corresponding to the double electron excitation of H₂. There exist in the spectrum three thresholds at 26.6±0.5 eV, 29.2±0.7 eV and 30.9±0.6 eV, and a dip at 34.1±0.5 eV. A Lyman-α excitation spectrum in the energy region corresponding to the single electron excitation has been also observed using a detection system which works as a band pass filter for detecting of Lyman-α fluorescence. The cross section of Lyman-α fluorescence in the photodissociation of the doubly excited states is very small, e.g., in the order of 10^?20 cm² at 30 eV, in comparison with that from the single electron excitation.     

Dissociative Excitation of Nickel Quintet States upon Electron Collisions with NiCl2Molecules

Dissociative excitation of nickel atom quintet states upon electron collisions with nickel dichloride molecules was studied by means of the extended crossed beams technique combined with optical spectroscopy. Forty excitation cross sections were measured at an electron energy of 100 eV. Two optical excitation functions were detected in the electron energy range 0–100 eV. Possible reaction channels at low electron energies were analyzed. Cross sections for dissociative excitation were compared to those for direct excitation upon electron collisions with nickel atoms.     

Elucidating the initial dynamics of electron photodetachment from atoms in liquids using variably-time-delayed resonant multiphoton ionization

We study the photodetachment of electrons from sodium anions in room temperature liquid tetrahydrofuran (THF) using a new type of three-pulse pump-probe spectroscopy. Our experiments use two variably-time-delayed pulses for excitation in what is essentially a resonant 1+1 two-photon ionization: By varying the arrival time of the second excitation pulse, we can directly observe how solvent motions stabilize and trap the excited electron prior to electron detachment. Moreover, by varying the arrival times of the ionization (excitation) and probe pulses, we also can determine the fate of the photoionized electrons and the distance they are ejected from their parent Na atoms. We find that as solvent reorganization proceeds, the second excitation pulse becomes less effective at achieving photoionization, and that the solvent motions that stabilize the excited electron following the first excitation pulse occur over a time of approximately 450 fs. We also find that there is no spectroscopic evidence for significant solvent relaxation after detachment of the electron is complete. In combination with the results of previous experiments and molecular dynamics simulations, the data provide new insight into the role of the solvent in solution-phase electron detachment and charge-transfer-to-solvent reactions.     

A possible contribution to the population of triplet states in electron impact measurements of total cross sections for triplet state excitation

It is proposed that low energy secondary electrons produced in medium energy electron impact experiments may play an important role in the excitation of triplet states even at low sample gas densities. A model calculation is carried out which shows that the population of the 4³S, S³P and 4³D triplet states in He from secondary electron excitation can be comparable to the population of these states by direct excitation at an incident electron energy of 1000 eV and sample gas pressures as low as 10^?3 torr. The model calculations show that the secondary electron mechanism becomes more important as the incident energy increases and that the produced populations are of a similar magnitude for the 3³P and 4³D states which in turn are about a factor of 4 larger than the population found for the 4³S state. The results indicate that the effect of secondary electron excitation in careful experimental measurements of electron impact total triplet state cross sections may have to be considered when incident electron excitation energies in the range of 1 keV or higher are used.     

Dissociative excitation of the singly charged lead ion in electron collisions with PbCl2 molecules

Inelastic collisions of slow electrons with lead dichloride molecules yielding excited lead ions in a single encounter event were studied by the extended crossed-beam technique. At an incident electron energy of 100 eV, 67 cross sections for dissociative excitation of PbII spectral lines were measured. Three optical excitation functions were determined in the electron energy range 0–100 eV. The obtained results are compared with data on excitation cross sections of PbII in electron-atom collisions.     

Monte Carlo simulation of full energy spectrum of electrons emitted from silicon in Auger electron spectroscopy

A Monte Carlo simulation including surface excitation, Auger electron‐ and secondary electron production has been performed to calculate the energy spectrum of electrons emitted from silicon in Auger electron spectroscopy (AES), covering the full energy range from the elastic peak down to the true‐secondary‐electron peak. The work aims to provide a more comprehensive understanding of the experimental AES spectrum by integrating the up‐to‐date knowledge of electron scattering and electronic excitation near the solid surface region. The Monte Carlo simulation model of beam–sample interaction includes the atomic ionization and relaxation for Auger electron production with Casnati's ionization cross section, surface plasmon excitation and bulk plasmon excitation as well as other bulk electronic excitation for inelastic scattering of electrons (including primary electrons, Auger electrons and secondary electrons) through a dielectric functional approach, cascade secondary electron production in electron inelastic scattering events, and electron elastic scattering with use of Mott's cross section. The simulated energy spectrum for Si sample describes very well the experimental AES EN(E) spectrum measured with a cylindrical mirror analyzer for primary energies ranging from 500 eV to 3000 eV. Surface excitation is found to affect strongly the loss peak shape and the intensities of the elastic peak and Auger peak, and weakly the low energy backscattering background, but it has less effect to high energy backscattering background and the Auger electron peak shape. Copyright © 2014 John Wiley & Sons, Ltd.     

On the redistribution of electrons for chemical reaction systems

A regional density-functional theory is formulated and applied to the study of ground-state electron redistributions during the course of a chemical reaction. If for a given increment of the reaction process, accumulation of electrons occurs in a certain region of space, then it is called the dynamic acceptor region, denoted by P. The complement is called the dynamic donor region, denoted by Q. The regional energy itself is determined as a unique functional of the electron density of the total system. The regional transfer potentials are defined in such a way that they add to give the total chemical potential, and their values along the reaction coordinate are found to be different between P and Q. The difference between the regional transfer potentials is shown to provide the driving force for electron transfer from Q to P. A characteristic coordinate for following electron transfer and an associated excitation potential are introduced. The excitation potential is a measure of regional virtual excitation due to regional interactions. The regional transfer potential gives the local character of electron transferability, while the excitation potential gives the global character. The theory encompasses the concepts of regional hardness and softness and sheds light on the HSAB principle.     

An atomic emission spectrometric method using the excitation of atoms by the electron flux

An atomic emission spectrometric method using the excitation of the atoms by the electron flux (AES-EAEF) is described. The atomic vapour, obtained by the electrothermal atomization of the analysed sample, is excited by the electron flux emitted from the same cathode-atomizer. Varying the voltage between the cathode and the anode, one may control the electron energy. Using helium as shielding gas with an ionization potential of 24.6 eV, an electron energy sufficient for the excitation of the analysed elements (the excitation potential for most elements is 2–10 eV), but not high enough for the ionization of helium, can be selected. Under these conditions, the self-maintaining plasma discharge is not formed, thereby minimizing the continuum background and maximizing the signal-to-noise ratio, the noise being due to the fluctuations of the background. The scheme of the unit for the AES-EAEF method is presented, and the effect of the different parameters on intensity of the signal and background have been studied. The absolute detection limits achieved with this method are comparable to those obtained using the technique of atomic absorption spectrometry with graphite furnace atomization.     

Formation of excited tin ion in collisions of slow electrons with SnCl2 molecules

Formation of excited tin ions in collisions of slow electrons with tin dichloride molecules was studied experimentally. Fifty excitation cross sections for SnII at an electron energy 100 eV were measured. Six optical functions for dissociative excitation were detected in the electron energy range 0–100 eV. Cross sections for direct and dissociative excitation of several lines were compared. Dissociative excitation in the spectral bands of two transitions in SnCl was also studied.     

Spectroscopic Diagnostics of Enhanced Magnetron and Mesh Separation Effects in Cyclonic Atmospheric Pressure Plasma Surface Modification of Polyethylene Terephthalate

The correlation of plasma surface modification consequence and the electron characteristics in plasma state with the enhanced magnetron source and metal mesh screen are studied by cyclonic-atmospheric-pressure plasma on polyethylene terephthalate (PET) surface. The contact angle measurement is employed to examine the plasma modified PET surface hydrophilicity. Optical emission spectroscopy is used to detect the electronic excitation temperature and electron density in cyclonic atmospheric pressure plasma. The electronic excitation temperature and the electron density are measured as the operational conditions of adding magnetron source and metal mesh separation. Boltzmann plot method is employed to estimate the electronic excitation temperature whereas electron density measurement by the Voigt profile. The results show that both electronic excitation temperature and electron density have similar trend i.e., both increasing with the enhanced magnetron source while decreasing trend is observed with passing through the metal mesh.     

Photodissociation of molecules of benzene and some of its derivatives in the liquid phase

The effect of intramolecular interactions on photodissociation has been studied. The quantum yields have been determined for the primary free radicals of benzene, its polymethyl-substituted derivatives Ph-(CH₃), and its monosubstituted Ph-(CH₂)-X derivatives, where X is a substituent containing a heteroatom. The conclusion made previously on the importance of singlet-singlet deactivation in nonradiative transitions of an excited molecule has been confirmed. The compounds Ph-(CH₂)-X have different photolytic stability on excitation by different normal vibrations within the limits of a single electron absorption band, A comparison of the spectral data with the photodissociation data for Ph-(CH₂)n-X enable us to propose that, depending on the nature of the intramolecular interactions, a transfer of both electron and vibrational excitation energy may take place from the ring to the substituent. This process is exceeded in the latter case by the conversion of electron excitation to vibrational excitation.We thank Professor Kh. S. Bagdasar'yan for his interest in the investigation and for discussion of the results.     

Dissociative Excitation Processes upon Collisions of Slow Electrons with MgBr2 Molecules

Dissociative excitation of MgI, MgII, and MgBr upon e–MgBr₂ collisions was experimentally studied. The excitation cross sections of the spectral lines of MgI and MgII, as well as two sets of bands of the MgBr molecule were measured at an incident electron energy of 100 eV. In the electron energy range from the excitation threshold to 100 eV, ten optical excitation functions with a complex structure were recorded. The principal pathways of dissociative excitation of MgI, MgII, and MgBr by slow electrons are discussed.     

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H(2)O and D(2)O from 8.3 to 12.4 eV

Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3 to 12.4 eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9 nm at 8.3 eV to nearly 4 nm at 12.4 eV, with the increase taking place most rapidly above 9.5 eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D(2)O, but is consistently shorter than in H(2)O by about 0.3 nm across the wide range of excitation energies studied.     

The fate of the dry electron—A preliminary investigation

A set of electron impact cross sections for vibrational excitation of water in the gaseous phase are first presented. The associated loss function is used in conjunction with a rotational loss function to generate efficiencies for the conversion of low-energy electron energy to rotational and vibrational excitation. An analogous calculation is carried out for intramolecular and intermolecular modes in the liquid phase leading to similar results. We also examine a simple model for the time dependence of the electron hydration process based on a square well with a time-dependent radius and well depth. We can fit the time and wavelength dependence of the experimental absorption coefficients if we introduce another time-dependent parameter that might be encompassed by a diffuse potential well model.     

Dissociative Excitation of Odd Triplet Levels of the Nickel Atom upon Electron Collisions with Nickel Dichloride Molecules

Dissociative excitation of odd triplet states of the nickel atom in collisions with slow monoenergetic electrons with nickel dichloride molecules was experimentally studied. The cross section values obtained are compared with the excitation cross sections in electron–atom collisions. Possible reaction channels at low electron energies are discussed. The results agree with previous data on the dissociative excitation of quintet states of the nickel atom.     

Estimation of the degree of ionization and the proportion of excited atoms in flame atomic spectrometry: a steady state approach

Summary A model is presented for the ionization of elements during flame atomic spectrometry, based on successive excitation of the electron to higher energy levels and finally the ionized state. The model is discussed in terms of a steady state involving thermal excitation, ionization, collisional excitation and collisional charge transfer interactions within the flame. Expressions are derived for the fraction ionized, and the fraction excited in terms of the rate constants for thermal excitation and radiative relaxation of the excited state. Data are presented showing good agreement between calculated and literature values for the fraction ionized for representative Group I and Group II elements.     

Experimental study of electron impact excitation of multiply charged ions

We report on measurements of angular differential cross sections for the excitation of multiply charged ions by electron impact. An ion beam is crossed by an electron beam; electrons which are inelastically scattered at different angles are identified by their energy loss due to the excitation process. Absolute excitation cross sections are obtained by comparing the signals of the elastic and the inelastic electron-ion scattering. Results obtained for the 3s→3p excitation of Ar⁷⁺ are discussed.     

Appreciation of a collisional-radiative model for the description of an inductively coupled argon plasma

The collisional-radiative model has been applied to the argon ICP discharge in order to elucidate the excitation mechanism in the plasma. The population density distributions of 25 argon energy levels were calculated under a steady-state approximation by using the literature values of electron number density, 5 × 10 ¹⁴cm^?3 and electron temperature, 9000 K. In the case of an optically thin plasma, in which the induced absorption can be neglected, the calculated population densities showed an overpopulation for low lying states, and were very close to LTE values for the upper levels. These results suggest the following excitation mechanisms in the argon ICP; corona model for lower levels and ladder-like excitation and ionization by electron impact for upper levels. According to the present calculation, the non-overpopulation of argon metastable can be interpreted by the interconversion between metastable and radiative states. It has been found that the induced absorption of resonance lines in an optically thick plasma and the motion of species in an inhomogeneous plasma have significant effects on the population densities. The non-linear processes by collision between heavy particles were not predominant compared to electron impact processes.     

Importance of the interference effect in atomic excitation and ionization accompanying inner-shell vacancy creation

A theoretical model for electron excitation and ionization of atoms following inner-shell ionization is presented. Both the sudden creation of an inner-shell vacancy and the Coulomb interaction between the ionized electron and atomic electrons are taken into account. The transition amplitude is written as the sum of the conventional shake process and the multipole transition due to the Coulomb interaction between electrons. The valence-shell excitation and ionization probabilities accompanying K-shell photoionization of Ne are calculated. It is found that the interference between the shake process and the Coulomb interaction enhances the probabilities at low energies.     

Spectroscopy on Rydberg states of sodium atoms on the surface of helium nanodroplets

One- and two-photon excitation spectra of sodium atoms on the surface of helium droplets are reported. The spectra are recorded by monitoring the photoionization yield of desorbed atoms as function of excitation frequency. The excitation spectra involving states with principal quantum number up to n = 6 can be reproduced by a pseudodiatomic model where the helium droplet is treated as a single atom. For the lowest excited states of sodium, the effective interaction potentials for this system can be approximated by the sum of NaHe pair potentials. For the higher excited states, the interaction of the sodium valence electron with the helium induces significant configuration mixing, leading to a failure of this approach. For these states, effective interaction potentials based on a perturbative treatment of the interactions between the valence electron, the alkali positive core, and the helium, as described in detail in the accompanying publication, yield excellent agreement with experiment.