Production of charge-induced X-rays during PIXE studies using light and heavy ion-beams

A recently discovered phenomenon of excessively high X-ray production is discussed. The high yield is attributed to the build-up of potential on non-conducting targets irradiated with accelerated ion beams, and the subsequent discharge. Ion-beams of¹H⁺,¹H₂ ⁺,²H⁺,²H₂ ⁺,³He⁺,³He²⁺,⁴He⁺,¹⁴N⁺,¹⁴N²⁺,¹⁶O⁺ and²⁰Ne⁺ were used. A new mechanism of X-ray excitation is proposed. The increased X-ray fluxes produced by this process are suitable for analytical applications of high specificity. The mechanism of excitation associated with the process, factors affecting the high X-ray yields, applications and a general overview of the studies undertaken with the various ion beams are given.     

In situ XPS and SIMS analysis of O2+ beam‐induced silicon oxidation

The chemical composition variation of silicon under 4 keV O₂⁺ ion beam bombardment at different incident angles was studied by in situ small‐area XPS. The changes in secondary ion profile (³⁰Si⁺, ⁴⁴SiO⁺, ⁵⁶Si₂⁺, ⁶⁰SiO₂⁺) during oxygen ion beam bombardment also have been monitored. We present a direct correlation of the changes in secondary ion depth profile with surface composition during sputtering. Evolution of the secondary ion profile obtained from SIMS shows similar trends with variation of oxygen concentration in the crater surface measured by XPS. It is shown that when the oxygen ion beam incidence angle is < 40° silicon dioxide is the dominant species on the crater surface and the matrix ion species ratio (MISR) value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is higher than for ³⁰Si⁺/⁵⁶Si₂⁺. For incidence angles of >40°, the formation of sub‐oxide is favoured and thus the MISR value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is lower than for ³⁰Si⁺/⁵⁶Si₂. At 40° bombardment there are similar amounts of SiO₂ and sub‐oxides present on the crater surface and the MISR values for ⁴⁴SiO⁺/⁵⁶Si₂⁺ and ³⁰Si⁺/⁵⁶Si₂⁺ are also similar. Copyright © 2004 John Wiley & Sons, Ltd.     

CI study of rovibrational dependence of nuclear quadrupole coupling constants of all isotopic variants of OH+ in the X3Σ− state

The ¹⁷O and ²H quadrupole coupling constants of rovibrational levels of ¹⁷O¹H⁺, ¹⁷O²H⁺, and ¹⁶O²H⁺ in their X³Σ⁻ state have been calculated from molecular wave functions that explicitly describe nuclear motion. The ¹⁷O quadrupole coupling is predicted to be strong and its vibrational dependence differs from that known for other nuclei A in the first-row hydrides AH or AH⁺. The deuterium coupling in ¹⁷O²H⁺ and ¹⁶O²H⁺ is found to be weak and its behavior is similar to that of other first-row hydrides. The change with rotational excitation is unimportant. The quadrupole hyperfine patterns of ¹⁷O²H⁺ in its ground state are dominated by the strong oxygen coupling. © 1996 John Wiley & Sons, Inc.     

Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

High-resolution UV photoelectron spectroscopy of diatomic halogens

Diatomic halogens are studied with UV photoelectron spectroscopy using new techniques to preserve high resolution even for reactive species. For the first time vibrational structure is observed on the ²Π_u,i (i = ^1/2,^3/2) states (F₂⁺, Cl₂⁺), the ²Σ_g⁺ states (F₂⁺, Cl₂⁺) and the Br₂⁺ (²Π_{u,$\text{3}\text{2}$}) state. On the ²Π_u,i states (F₂⁺, Cl₂⁺, Br₂⁺) spin-orbit splitting is resolved. Indications for a small potential barrier on the F₂⁺ (²Π_u,i) state for large internuclear distances are found. A new value for the spin-orbit splitting of the Cl₂⁺(²Π_g) state is presented (= ?725 cm^?1). The complementary nature of optical emission and photoelectron spectroscopy for small ions is demonstrated leading to a more complete picture of the F₂⁺ (²Π_u,i) and Cl₂⁺ (²Π_u,i) ionic states.     

Multiple magnetic resonance studies of some para-substituted derivatives of triphenyl phosphine

¹⁹F and ³¹P decoupling experiments are used to simplify the proton spectra of para-substituted derivatives of triphenyl phosphine, prior to ¹H-{¹H} tickling experiments. ³J(³¹P…?H) and ⁴J(³¹P…?H) are positive, and ⁵J(³¹P…?¹⁹F) is negative in the trivalent phosphorus derivatives, and all become more positive as the valency of the phosphorus atom is increased. A triple resonance experiment is used to show that ⁷J(³¹P…?H) in [p-CH₃C₆H₄CH₂P^⊕(C₆H₅)₃] is negative. The double resonance technique is used to relate the ³¹P chemical shifts to the tetramethylsilane resonant frequency.     

Cubic phases of binary systems of 4′-n-tetradecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-14)-n-alkane

The phase behaviour of the binary systems 4′- ⁿ -tetradecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-14)- ⁿ -alkane ( ⁿ -tetradecane or ⁿ -hexadecane) was investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The phase behaviour was a function of temperature ( ^T ) and the effective carbon number of the system ( ^n*), where ^n* involves carbon atoms both from the alkoxy group of ANBC-14 and from the ⁿ -alkane added. ANBC-14 shows no cubic phase, but the addition of ⁿ -alkane induced cubic phases when ^n*≧c. 15. An interesting point is that the type of cubic phase is ^Ia 3 ^d for 15^≦n*≦17, while an ^Im 3 ^m type is formed for 18^≦n*≦20. Furthermore, for ^n* = 22, two types of cubic phase, one with ^Im 3 ^m symmetry in the low temperature region and the other with ^Ia 3 ^d in the high temperature region, were observed both on heating and cooling. The phase diagram with respect to ^T and ^n* is very similar to that of pure one-component ANBC- ⁿ , which is a function of ^T and the number of carbon atoms in the alkoxy group ⁿ .     

Heterodyne measurements of hot bands and isotopic transitions of N2O near 7.8 µm

Heterodyne frequency measurements are reported for absorption transitions of N₂O in the frequency range from 1257 to 1335 cm^?1. The measurements use a CO laser as a transfer oscillator whose frequency is measured directly against combinations of frequencies of two stabilized CO₂ lasers whose frequencies are well known. A tunable diode laser is locked to the N₂O absorption feature and the frequency difference is measured between the diode laser and the CO laser. Thev ₃ fundamental bands of the¹⁵N¹⁴N¹⁶O and¹⁴N¹⁵N¹⁶O isotopes are reported. Measurements are also given for the 00⁰2–00⁰1, 02⁰1–02⁰0, and 02²1–02²0 vibrational transitions of N₂O. A table of frequencies is given for the 00⁰2–00⁰0 band near 2560 cm^?1 based on these and earlier measurements.     

ANTENNA EFFECT IN LUMINESCENT LANTHANIDE CRYPTATES: A PHOTOPHYSICAL STUDY

Excited state emission and absorption decay measurements have been made on the cage-type cryptate complexes [M bpy.bpy.bpy]ⁿ⁺, where Mⁿ⁺= Na⁺, La³⁺, Eu³⁺, Gd³⁺ or Tb³⁺ and [bpy.bpy.bpy] is a tris-bipyridine macrobicyclic cryptand. Excitation has been performed in the high intensity ¹π-π* cryptand band with maximum at about 300 nm. Experiments have been carried out in H₂O or D₂O solutions and at 300 and 77 K to evaluate the rate constants of radiative and nonradiative decay processes. For Mⁿ⁺= Na⁺, La³⁺ and Gd³⁺ the lowest excited state of the cryptate is a ³ππ* level of the cryptand which decays in the microsecond time scale at room temperature in H₂O solution and in the second-millisecond time scale at 77 K in MeOH-EtOH. For Mⁿ⁺= Eu³⁺, the lowest excited state is the luminescent ⁵D₀ Eu³⁺ level which in H₂O solution is populated with 10% efficiency and decays to the ground state with rate constants 2.9 × 10³ s^_1 at room temperature and 1.2 × 10³ s^?′ at 77 K. The relatively low efficiency of ⁵D₀ population upon ¹ππ* excitation is attributed to the presence of a ligand-to-metal charge transfer level through which ¹ππ* decays directly to the ground state. For Mⁿ⁺= Tb³⁺ the lowest excited state is the luminescent ⁵D₄ Tb³⁺ level. The process of ⁵D₄ population upon ¹ππ* excitation is ?100% efficient, but at room temperature it is followed by a high-efficiency, activated back energy transfer from the ⁵D₄ Tb³⁺ level to the ³ππ* ligand level because of the relatively small energy gap between the two levels (1200 cm^_1) and the intrinsically long lifetime of ⁵D₄. At 77 K back energy transfer cannot take place and the ⁵D₄ Tb^3* level deactivates to the ground state with rate constant 5.9 × 10² s^-′ (H₂O solution). The relevance of these results toward the optimization of Eu³⁺ and Tb³⁺ cryptates as luminescent probes is discussed.     

Energy transfer between Bi3+ and Nd3+ in germanate glass

Energy transfer from Bi³⁺ to Nd³⁺ is reported in germanate glass. It was found that the excitation range and intensities of the ⁴F_{$\text{3}\text{2}$} → ⁴I_{$\text{9}\text{2}$}, ⁴I_{$\text{11}\text{2}$} emissions are increased several fold when excited through ¹S₀ → ³P₁ absorption of Bi³⁺. It is shown that the energy transfer is nonradiative. The energy transfer probability and efficiency were calculated from the Bi³⁺ fluorescence decay rates and intensities. The Bi³⁺ → Nd³⁺ energy transfer may be utilized in Nd³⁺ glass laser.     

CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

The predissociations of water ions

Experimental relative abundances of D₂O⁺, OD⁺ and D⁺ ions are given as functions of the initial energy of D₂O⁺ ions in the B?²B₂ state. The D⁺ ions are more abundant than expected on the basis of a recent theoretical model. Less kinetic energy is released in D⁺ formation than in OD⁺ formation, for the same excess energy available. It is suggested that OD⁺ formation should be modelled as a statistical reaction, whereas D⁺ formation is more specific. No detailed model can be suggested on present evidence, but it is pointed out that H₂O⁺ (B?²B₂) can be predissociated to OH⁺ by the X? state to H⁺ by the à state, as well as by repulsive states.     

The Reaction of Ozone with the Hydroxide Ion: Mechanistic Considerations Based on Thermokinetic and Quantum Chemical Calculations and the Role of HO4− in Superoxide Dismutation

The reaction of OH^? with O₃ eventually leads to the formation of ^.OH radicals. In the original mechanistic concept (J. Staehelin, J. Hoigné, Environ. Sci. Technol. 1982 , 16, 676–681), it was suggested that the first step occurred by O transfer: OH^?+O₃→HO₂^?+O₂ and that ^.OH was generated in the subsequent reaction(s) of HO₂^? with O₃ (the peroxone process). This mechanistic concept has now been revised on the basis of thermokinetic and quantum chemical calculations. A one‐step O transfer such as that mentioned above would require the release of O₂ in its excited singlet state (¹O₂, O₂(¹Δ_g)); this state lies 95.5 kJ mol^?1 above the triplet ground state (³O₂, O₂(³Σ_g^?)). The low experimental rate constant of 70 M ^?1 s^?1 is not incompatible with such a reaction. However, according to our calculations, the reaction of OH^? with O₃ to form an adduct (OH^?+O₃→HO₄^?; ΔG=3.5 kJ mol^?1) is a much better candidate for the rate‐determining step as compared with the significantly more endergonic O transfer (ΔG=26.7 kJ mol^?1). Hence, we favor this reaction; all the more so as numerous precedents of similar ozone adduct formation are known in the literature. Three potential decay routes of the adduct HO₄^? have been probed: HO₄^?→HO₂^?+¹O₂ is spin allowed, but markedly endergonic (ΔG=23.2 kJ mol^?1). HO₄^?→HO₂^?+³O₂ is spin forbidden (ΔG=?73.3 kJ mol^?1). The decay into radicals, HO₄^?→HO₂^.+O₂^.?, is spin allowed and less endergonic (ΔG=14.8 kJ mol^?1) than HO₄^?→HO₂^?+¹O₂. It is thus HO₄^?→HO₂^.+O₂^.? by which HO₄^? decays. It is noted that a large contribution of the reverse of this reaction, HO₂^.+O₂^.?→HO₄^?, followed by HO₄^?→HO₂^?+³O₂, now explains why the measured rate of the bimolecular decay of HO₂^. and O₂^.? into HO₂^?+O₂ (k=1×10⁸ M ^?1 s^?1) is below diffusion controlled. Because k for the process HO₄^?→HO₂^.+O₂^.? is much larger than k for the reverse of OH^?+O₃→HO₄^?, the forward reaction OH^?+O₃→HO₄^? is practically irreversible.     

Trennungen von Kationen in Titanhexacyanoferrat(II)-S?ulen

Zusammenfassung Die Trennung der Ionenpaare Rb⁺/Cs⁺, K⁺/Rb⁺, K⁺/Cs⁺, Na⁺/K⁺, Li⁺/Na⁺ mit Salzsäure oder Ammoniumchloridlösung als Elutionsmittel gelingt quantitativ oder nahezu quantitativ mit Hilfe von Titanhexacyanoferrat(II)-säulen. Die Cäsiumionen können nicht eluiert werden. Ebenso gelingt die Trennung der lonenpaare Sr²⁺/Ba²⁺, Ca²⁺/Ba²⁺, Ba²⁺/Cs⁺ und Sr²⁺/Cs⁺ quantitativ oder nahezu quantitativ. Auch eine partielle Trennung der Seltenen Erden ist möglich; Yttrium ist leichter eluierbar als die Lanthanide.

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Summary The quantitative or nearly quantitative separation of the ion pairs Rb⁺/Cs⁺, K⁺/Rb⁺, k⁺/Cs⁺, Na⁺/K⁺ and Li⁺/Na⁺ can be achieved with hydrochloric acid or ammonium chloride solutions as eluents by means of columns of titanium hexacyanoferrate(II). The elution of the Cs⁺ ions is not possible. In the same way the quantitative or nearly quantitative separation of the ion pairs Sr²⁺/Ba²⁺, Ca²⁺/Ba²⁺, Ba²⁺/Cs⁺ and Sr²⁺/Cs⁺ can be achieved. Also a partial separation of the rare-earth elements is possible; yttrium is more easily eluted than the lanthanides.

     

Signs of proximate 31P, 19F and 19F, 19F spin–spin coupling constants in 2-trifluoromethylphenyldifluorophosphine

In 2-trifluoromethylphenyldifluorophosphine the proximate couplings ⁴J(¹⁹F³¹P) and ⁵J(¹⁹F¹⁹F) are + 68.3 and + 8.3 Hz, respectively. ¹J(¹³C³¹P) is ?57.0 Hz, ²J(¹³C-1, ¹⁰F) is + 9.9 Hz and ²J(¹³C-6, ¹³C-6, ³¹P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the ³¹P and ring ¹³C nuclei.     

Theoretical study of the π→π* excited states of linear polyenes: The energy gap between 11Bu+ and 21Ag− states and their character

Multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions is applied to the study of the valence π→π* excited states of 1,3-butadiene, 1,3,5-hexatriene, 1,3,5,7-octatetraene, and 1,3,5,7,9-decapentaene. Our focus was put on determining the nature of the two lowest-lying singlet excited states, 1¹B_u⁺ and 2¹A_g⁻, and their ordering. The 1¹B_u⁺ state is a singly excited state with an ionic nature originating from the HOMO→LUMO one-electron transition while the covalent 2¹A_g⁻ state is the doubly excited state which comes mainly from the (HOMO)²→(LUMO)² transition. The active-space and basis-set effects are taken into account to estimate the excitation energies of larger polyenes. For butadiene, the 1¹B_u⁺ state is calculated to be slightly lower by 0.1 eV than the doubly excited 2¹A_g⁻ state at the ground-state equilibrium geometry. For hexatriene, our calculations predict the two states to be virtually degenerate. Octatetraene is the first polyene for which we predict that the 2¹A_g⁻ state is the lowest excited singlet state at the ground-state geometry. The present theory also indicates that the 2¹A_g⁻ state lies clearly below the 1¹B_u⁺ state in decapentaene with the energy gap of 0.4 eV. The 0–0 transition and the emission energies are also calculated using the planar C_2h relaxed excited-state geometries. The covalent 2¹A_g⁻ state is much more sensitive to the geometry variation than is the ionic 1¹B_u⁺ state, which places the 2¹A_g⁻ state significantly below the 1¹B_u⁺ state at the relaxed geometry. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 157–175, 1998     

硫族铅化物阳离子低电子态的理论研究

采用我们最近发展的含旋轨耦合的运动方程耦合簇计算电离能(EOMIP-CC)方法,在CCSD级别上计算了硫族铅化物PbS、PbSe、PbTe阳离子低电子态的平衡键长和谐振频率以及绝热和垂直电离能,得到的结果与已有的实验值吻合较好.不考虑旋轨耦合(SOC)的情况下通过与CCSD(T)的计算结果比较,考察了三重激发对计算结果的影响,结果显示考虑三重激发的贡献后得到的键长和频率结果与实验值吻合更好.计算结果表明PbTe+中2Π态的能量分裂明显大于PbS+和PbSe+中2Π态的能量分裂,但是PbTe+中2Π1/2和2Σ1/2态之间的相互耦合则明显弱于PbS+和PbSe+中这两个态之间的耦合.PbTe+中2Π1/2和2Σ1/2态之间耦合很弱,一方面是因为2Σ+态和2Π态的能量差比PbS+和PbSe+中2Σ+态和2Π态的能量差大,另一方面还由于PbTe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元只是PbS+和PbSe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元的一半.这些计算结果为PbS+、PbSe+、PbTe+阳离子的低电子态性质提供了新的理论数据,可以为将来的实验数据提供参考.     

Dynamics of reactions of O(3P) atoms with CS,CS2 and OCS

The reactions of CS(X ¹Σ⁺), CS₂(X ¹Σ⁺_g) and OCS(X ¹Σ⁺) with O(³P) were studied at 298 K by means of a CO laser resonance absorption technique. The CO(ν) population distribution produced from the reaction O(³P) + CS(X ¹Σ⁺) studied in a quartz flash photolysis tube (λ>/ 200 nm) is similar to distributions observed previously for ν> 7. For ν < 7 an energetically colder vibrational population was observed which is attributed to the reaction of O(³P) atoms with undissociated CS₂(X ¹Σ⁺_g). Subsequent experiments carried out in a Pyrex flash photolysis tube (λ>/ 300 nm) in which the O(³P) + CS₂(X ¹Σ⁺_g) reaction is the only one which can occur confirmed that the colder population observed is attributable to this process. The branching ratio for the reaction channel O(³P) + CS₂(X ¹Σ⁺_g) → CO(X ¹Σ⁺) + S₂(³Σ^?_g) has been measured. We find that 1.4 ± 0.2% of the O + CS₂ reaction proceeds through this channel, and that the rate constant for this reaction channel is, k = 3.5 (±0.5) × 10¹⁰ cm³/mole s. Isotope labeled experiments using ¹⁸O atoms show that the O(³P) + OCS(X ¹Σ⁺) reaction takes place by a direct stripping mechanism, wherein CO(ν) is produced exclusively from the parent OCS molecule. The CO(ν) formed in this reaction carries about 9% of the total available energy.     

Relaxation of the 1000 lower laser level in CO2

The relative importance of the relaxation processes of the 10⁰0 level of CO₂ is shown to be dependent on the experimental conditions. The rate coefficient for the exchange of energy between the 10⁰0 and 01¹0 levels is found as 10⁴ torr ^? sec^?1 and the coefficient for the exchange between the 10⁰0 and 02⁰0 or 02²0 levels as 3 × 10⁵ torr^?1 sec^?1.     

Ab initio calculations of infrared transition rates in the ground states of BF and BF+

Electric dipole moment functions and radiative transition rates have been calculated for the X¹Σ⁺ state of BF and the X²Σ⁺ state of BF⁺ from MC SCF wavefunctions. Both are predicted to be strong emitters in the infrared. For BF⁺ the electronically excited ²Σ⁺ state, corresponding to the configuration 1σ²2σ²3σ²4σ5σ²1π⁴, is calculated to be bound, whereas the A ^Π state is repulsive.