Doubly-charged Ions Research Articles

Direct observation of vibrational states of CO2+ and N22+ by threshold photoelectrons coincidence spectroscopy

Double ionization of CO and N2 induced by photons from a synchrotron radiation source has been studied in an electron-electron coincidence experiment. A new technique for this type of study has been developed wherein only electrons with near-zero energy are detected by the use of the penetrating field method. In this way high sensitivity and energy resolution have been attained and this has allowed vibrational structure to be observed for the doubly-charged ions of both these molecules and accurate energies for the states to be obtained.

Comparative Study of the Decay Mechanisms for 4d Resonances of lodine and 3p Resonances of Copper

This paper describes the approximations which allow to calculate the rates of the various decay processes for core resonances below inner-shell thresholds of open-shell atomic system (4d thresholds of iodine and 3p of copper). Moreover, it emphasizes the different mechanisms that predominantly produce either singly-charged ions when a valence state decay is considered, or doubly-charged ions in case of an excitation to a level of a Rydberg series. Despite different decay mechanisms, the main conclusions are similar to those obtained for closed-shell atoms. In particular, the rate of the double Auger with the Rydberg electron spectator or nearly spectator (shake-up process) in the first step is increasing as soon as the first resonances but this decay path is progressively replaced by shake-off (2 electrons ejected simultaneously) whose rate is increasing with the principal quantum number n of the Rydberg electron.

Molek�lgeometrie und angeregte Elektronenzust�nde. XXIV. Theoretischer Beitrag zur S0 und S1-Molek�lstruktur und zum elektronischen Sp? S0-Spektralverhalten des 1,4-Distyryl-benzols und seiner doppelt-geladenen Ionen

Molecular Geometry and Excited Electronic States. XXIV. Theoretical Contribution to the S0 and S1 Molecular Structure and to the Sp S0 Electronic Spectral Behaviour of 1,4-Distyryl Benzene an of its Doubly-Charged Ions For selected configurations of 1,4-distyryl benzene and its doubly-charged ions the completely-optimized molecular geometries of the S0 and S1 states are presented. The structural peculiarities and differences are discussed. The Sp S0 electronic spectral data calculated on this basis are given and compared with available experimental results.

Dissociative charge transfer of singly- and doubly-charged rare gas ions with W(CO) 6

Charge exchange of the thermometer compound, W(CO) 6, with singly-charged rare gas ions yields internally excited W(CO) + 6 molecular ions. The internal energy distribution, P(ε), of the nascent ions is estimated by an approximate thermochemical method which is based on dissociation by successive CO losses. The average internal energy agrees well with expectation based on the known values of the rare gas recombination energies. The distribution of internal energies have half widths of 1–3 eV and maxima which correspond to the calculated heats of reaction. Energy deposition is only a weak function of collision energy, increasing by a few tenths of an electronvolt in the range 2.5–10 eV, and then remaining constant to 30 eV. Singly-charged argon and neon ions, but not the other singly-charged rare gas ions, show production of doubly-charged metal carbonyls due to contributions from Ar + and Ne + in long-lived excited states. Charge exchange of W(CO) 6 with the doubly-charged rare gas ions shows three prominent processes: (i) single-electron transfer, which is accompanied by average internal energy depositions as high as 15 eV and gives products with wider and more asymmetric internal energy distributions than those which occur by charge exchange with the singly-charged rare gas ions; (ii) double-electron transfer to generate doubly- charged tungsten hexacarbonyl ions, W(CO) 2+ n and WC(CO) 2+ n ; and (iii) the formation of unexcited W(CO) + 6 ions resulting from charge exchange between the nascent doubly-charged ion and neutral W(CO) 6. The maxima of the P(ε) curves for both single and doubel electron transfer agree with thermo-chemical predictions except that there is a small, systematic, difference in energy deposition for the single-electron transfer process which is ascribed to mutual coulombic repulsion of the products. Doubly-charged neon yields both ground state and excited state Ne + . The average internal energies for both single- and double-electron transfer are almost independent of the laboratory collision energy, indicating that long-range electron transfer is involved.

Mechanism of production and the current density effects of doubly charged ion emission from Cd+-bombarded Nb and V targets

Abstract Secondary emission of doubly-charged postive ions from 3–15 keV Cd+ ion-bombarded polycrystalline Nb and V samples at target current densities (Jp ) in the range 0–1.4 mA cm−2 has been studied in detail. For each target the ratio of doubly-charged to singly-charged ion currents (Is ++ /Is ++)has been found to be 0.01 at low beam current densities and does not vary appreciably with increase in the primary ion current (Ip ), there is a rapid increase in the value of Is ++ as compared to I+ s such that at Jp ∼ 15μm UA cm−2, the ratio Is ++/Is + increase by 10 to 300 times depending upon the target and bombarding conditions. The value of Jp at which maximum enhancement of Is ++ is observed often corresponds to the saturation region in the current density variation curve, observed in case of singly-charged ion emission. This region possibly corresponds to the formation of an intermetallic compounds layer of a definite stochiometric composition due to the action of reactive Cd+ ions at the metallic tar...

A possible search for doubly-charged negative ions

An alternative approach to the search for doubly-charged negative ions is proposed. It involves the use of singly-charged negative ions of positron emitters for possible production of doubly-charged negative ions. Accelerators and ion traps are considered for use in the search.

Ionization energies of the cations of metallocene (M(C 5H 5) +2), their half-sandwich complexes MC 5H +5 and the bare transition-metal ions M + (M = Fe, Co, Ni)

Charge stripping experiments indicate that in the reaction M + → M 2 + e − the doublycharged transition-metal ions M 2+ (M = Fe, Co, Ni) are formed in excited states. Introduction of one or two C 5H 5 ligands drastically reduces the Q min values of the reaction M(C 5H 5) + x → M(C 5H 5) 2+) x + e − (x = 1, 2) by at least 3.5 eV. The experimental findings support existing molecular orbital concepts of metallocene compounds.

An estimating formula for ion–atom association rates in gases

We derive a simple estimating formula for rate coefficients of three-body ion atom association in gases and compare its predictions to experimental data on ion association and three-body radiative charge transfer reactions of singly- and doubly-charged rare-gas ions. The formula appears to reproduce most experimental data quite well. It may be useful for estimating the rates of reactions that have not been studied in the laboratory.

Evidence from SIMS of Doubly-Charged Boron Contamination During Singly Charged-Ion Implantation

When a dopant is introduced into a semiconductor material by ion implantation, it is sometimes desirable to accelerate and implant the ion in a multiply-charged state. This has the effect of increasing the energy and range of the ion without increasing the accelerating potential. Most modern ion implanters are of the pre-analysis type. In this design the ions are first accelerated through a modest extraction potential, e.g., 25 keV. This is followed by deflection for mass-to-charge selection in an analyzer magnet, after which the selected ions undergo final acceleration. Charge-exchange reactions between the doubly-charged ions and residual gas have been found to occur between the analyzing magnet and the final acceleration section. These reactions produce singly-charged ions that receive only half of the energy of the doubly-charged ions during final acceleration. For the case of B++ implantation the resulting implant profile shows a shallow-depth shoulder due to B+, the amplitude of which may be greater than 50% of the main peak.

Studies on ion formation in a glow discharge mass spectrometry ion source

The relative populations of singly- and mutiply-charged argon, matrix and argide ions in an Ar-glow discharge have been measured in different matrices using the VG-9000 glow discharge mass spectrometer. The measured relative densitites of multiply-charged argon ions (from +3 to +6) are in good agreement with the Lovett rate model for electron impact ionization/three-body recombination with an electron temperature of about 7 eV (R.J. Lovett, Spectrochim. Acta, 37B, 985 (1982)). An overpopulation of singly- and doubly-charged argon ions relative to this relationship has been observed in all cases. The overpopulation of singly-charged argon ions is caused by a process of quenching of metastables in a doubly excited system. So-called “secondary electrons” with an average energy about 7 eV produced in this reaction can be an agent creating multiply-charged argon ions. Sputtered sample/cathode atoms are ionized mainly by Penning ionization (PI). A dominance of PI has been found in the production of singly- and multiply-charged ionic species for which ionization energies are lower than the energy of argon metastable atoms. The remaining species appear to be ionized by the secondary electrons.

Photoelectron-photoelectron coincidence spectroscopy

Photoelectron-photoelectron coincidence spectra taken using a fixed-wavelength laboratory instrument show certain states of molecular doubly-charged ions. They are complicated, however, by a phenomenon of non-resonant autoionization, whose existence is now revealed.

Multiple photoionisation of Cs and Ba atoms due to creation of 4d hole states

Multiple photoionisation processes of Cs and Ba atoms due to creation of 4d hole states have been studied by measurement of photoion-yield spectra (energy dependence of photoion yield). Monochromatised synchrotron radiation was used to excite the 4d-shell electron, and measurements were made in the energy regions from the neighbourhood of the 4d-nl resonance excitation to the higher-energy tail of the big 4d- in f shape resonance. The main products in these regions are doubly-charged (Cs2+, Ba2+) and triply-charged (Cs3+, Ba3+) ions, and an appreciable number of Cs4+ and Ba4+ ions starts being produced around the lowest photoelectron shake-off (4d-1nl-1) and shake-up (4d-1nl-1n'l') states, respectively. Although the relaxation of the 4d hole states proceeds mainly through stepwise processes consisting of the normal Auger process and autoionisation, Auger shake-off processes are found to have considerable probabilities (typically 0.19-0.38 in the case of Cs) in the first stage of the relaxation. The shake-off probability associated with the 4d photoionisation in Cs estimated from the present data amounts to 0.33+or-0.05 in the region of the higher-energy tail of the shape resonance.

Semi-quantitative method for high molecular weight neuropeptides by high-performance liquid chromatography/thermospray mass spectrometry

High-performance liquid chromatography/thermospray mass spectrometry (HPLC/MS) was evaluated and optimized for the determination of beta- and gamma-endorphin. Thermospray spectra for the endorphins could be acquired under ion evaporation conditions, when a low vaporizor temperature (94 degrees C) and high source temperature are used. The spectra showed [M + H]+, [M + Hx-1 + Nax]+(x = 1-3) together with double charged ions. Positive ion detection exhibited higher ion currents than negative ion detection. Thermospray HPLC/MS was used to generate a linear calibration curve from 10 to 300 pmol. Thermospray displayed good run-to-run reproducibility (2-7%) and accurately measured spiked quantities of beta- and gamma-endorphin within 15% of the spiked values.

Hydrodynamics of double-charged ions in a plane low-pressure discharge

A model of a plane low-pressure discharge with double ionisation is studied. Effects of gas depletion and friction between both species of ions are also considered. The transverse electron density distribution is shown to have a maximum on the axis, whereas a dip appears in the centre of a single-charged ion profile. Estimates are presented for the argon-laser plasma, in which such a dip has been observed in recent measurements of the spontaneous emission radial distribution.

Observation of doubly-charged dimer ion emission in liquid-metal-ion sources

Liquid-metal-ion sources (LMIS's) emit atomic and cluster ions. In the mass analysis of LMIS's using Au-Sb and Pt-Sb alloys, the doubly-charged dimer ions Sb 2+ 2 are observed as well as the doubly-charged diatomic ions AuSb 2+ and PtSb 2+. The flux abundance of Sb 2+ 2 in Sb + +Sb 2+ 2 for a Au-Sb alloy is approximately 20%, which is larger by one order of magnitude than that for a Pt-Au alloy. It is predicted that the stability of cluster ions is strongly affected by the electrostatic field near the ion emitter. The formation mechanism of M 2+ 2 ions is discussed using mass spectra and energy distribution curves.

Observation of doubly-charged dimer ion emission in liquid-metal-ion sources

Observation of doubly-charged dimer ion emission in liquid-metal-ion sources

Observation of doubly-charged dimer ion emission in liquid-metal-ion sources

Observation of doubly-charged dimer ion emission in liquid-metal-ion sources

Doubly-charged positive ions following loss of oxygen dianion under conditions of field desorption mass spectrometry

A number of cyclic aromatic anhydrides have been found to exhibit doubly-charged positive ions in their field desorption mass spectrum which correspond to the formal loss of oxygen dianion followed by clustering with a neutral molecule. Admixtures of two anhydrides, which both exhibit this phenomenon, produce heterogeneous doubly-charged cluster ions. Admixture with anhydrides which do not show the effect, produces only homogeneous clusters at reduced intensity.

Singly and doubly charged ion collisions with neutrals into excited states

Recent experimental results on charge transfer into excited states in collisions between singly and doubly charged ions with He, Ne, Ar, H 2 and O 2 are presented, respectively. The energy range of the ion beams of He q+, Ar q+, Ne + ( q = 1,2) ions is (70–170)× q keV. The optical measurement was performed by an Optical Multichannel Analysis System (OMA). The wavelength range covered was 200–800 nm. Different processes of excitation have been observed in single and double charged ion collisions with neutrals. The dependence of emission cross sections on the potential energy defect is discussed.

Charge separation mass spectrometry 1. Doubly-ionized perfluoro compounds

Perfluoro compounds have been used as model compounds to investigate the charge separation mass spectra of polyatomic molecules using a triple coincidence photoionization technique. The two-dimensional m 1 − m 2 spectra contain detailed information on the doubly-charged ion breakdown pathways, and show the importance of both primary and secondary loss of neutral fragments. The major characteristics of the reactions are rationalized by a simple model, which can also be used to predict the characteristics of charge separation in other classes of compound and following triple or higher ionization.