Electron spectroscopy using excited atoms and photons IX. Penning ionization of CO2, CS2, COS,N2O,H2S,SO2, and NO2

The electron spectra resulting from thermal collisions of He* (predominantly 2³S) metastable atoms with the seven triatomic molecules, CO₂, COS, CS², N₂O H₂S, SO₂ and NO₂, are compared with their respective 584-Å photoelectron spectra using a transmission-corrected electron spectrometer. The normalised relative electronic-state transition probabilities for production of ionic states in Penning ionization and photoionization are reported together with energy shifts (ΔE values) for He*(2³S) Penning ionization. The cross-section for Penning ionization to lower states of NO₂⁺ is extremely low as has been observed in other open shell molecules such as NO and O₂.     

Penning ionization electron spectroscopy of H2O,D2O,H2S and SO2

Electron energy peak shifts and peak shapes were determined in the ionization of H₂O, D₂O, H₂S and SO₂ by Ne(³P₂) and He(2¹S, 2³S) metastable atoms. The shifts are large, especially in ionization of H₂O and D₂O into the ionic ground state and are probably mostly due to chemical interaction during the collision.In a previous paper the electron energy distribution curves for ionization of CO, HCl, HBr, N₂O, NO₂, CO₂, COS and CS₂ by helium, neon and argon metastables and the characteristics of this ionization were described¹. In this paper the series of triatomic molecules was extended to the molecules H₂O, D₂O, H₂S and SO₂. Because all these molecules have considerable dipole moments it could be expected that the peak shifts might be enhanced as compared with other triatomic molecules.     

Velocity dependence of the chemi-ionization of H2O and D2O on impact of 21S and 23S helium atoms

The velocity dependence for the ionization of H₂O and D₂O to form H₂O⁺ and D₂O⁺ in collisions with both 2³S and 2¹S metastable helium atoms has been measured in a crossed molecular beam apparatus using a mechanical velocity-selector on the metastable beam. The cross-sections are found to be proportional to the —n power of the relative collision energy, with n ? 0.4 for both metastable atoms in both gases. The branching ratios H₂O⁺/OH⁺ and D₂O⁺/OD⁺ were both found to be 4.3 for both metastable helium atoms, and to be independent of the relative collision energy.     

Penning ionization electron spectroscopy and photo-electron spectroscopy of molecular solids. II. Ammonia and water

The Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) of ammonia and water molecules condensed on a cold metal substrate have been measured using thermal He*(2³S, 2¹S) metastable atoms and He(I) (58.4 nm) photons. The shifts of the observed positions of the PIES peaks relative to those of the UPS peaks in the condensed phase are roughly equal to the corresponding shifts in the gas phase. The relative intensities of the 3a₁ and 1e orbital peaks are reversed in the PIES and UPS for both gaseous and condensed ammonia; the origin of this reversal is interpreted as the difference between the interactions with metastable atoms and photons. On the other hand, the relative intensities of the 3a₁ orbital peak in the PIES and UPS for condensed water decrease as compared to the gas-phase spectra. This implies participation of the 3a₁ orbital of water in the hydrogen bonding.     

Ionization by H+2. Molecular effect

The molecular effect in the ionization of inner shell electrons of aluminum atoms by energetic H⁺₂ molecules has been calculated. We distinguish between the molecular effect in Al and Al₂O₃. We conclude that in the case of Al the protons of the cluster have a definite orientation but in the case of Al₂O₃ the orientation is at random.     

The temperature dependence of penning ionization electron energy spectra: He(23S)—ar,N2, NO,O2, N2O,CO2

Using two intense thermal energy He(2³S) sources of different temperatures (≈400 and ≈ 1000 K, resp.) and a transmission-calibrated electron energy analyzer with about 30meV resolution, the dependence of He(2³S) Penning ionization electron spectra on collision energy for the target species Ar, N₂, NO, O₂, N₂O and CO₂ have been studied. The energy shifts of the Penning electron energy distributions and the branching ratios for the population of different electronic states in the molecular ions are determined quantitatively and compared for the two different collision temperatures. These results and the shapes of the observed Penning electron energy distributions are discussed in the light of current models for the Penning procen; the observed temperature dependences are correlated with the nature of the ionized orbitals in cases of only one entrance channel (closed shell targets) and, in addition, to the existence of qualitatively different entrance channels (open shell targets).     

Ion-electron coincidence study of the thermal He(23S) + H2 Penning reaction

A new Penning-electron-Penning-ion coincidence method is described. It is applied to the study of the thermal reaction of He(2³S) with H₂. The main results reported are separate electron energy spectra that are coincident with the three different ions formed: HeH₂⁺, HeH⁺ and H₂⁺. Based on these results it is shown that the Penning reaction of the He(2³S)/H ₂ system proceeds in two well-separated steps: (i) ionization at distances R (HeH₂) ? 6a₀ in which H₂⁺ (v) is formed in different vibrational states; and (ii) reactive collision of H₂⁺ (v) with He. For the second step the variation of the branching ratios with vibrational quantum numbers v = 0 to v = 10 is derived, and it is shown that these branching ratios may be regarded as relative vibrational-energy-dependent cross-sections for the collision of H₂⁺ (v) with He at an average relative kinetic energy of ～20 meV.     

Duree de vie et facteur de lande du niveau (5s5p2)4P12 de L'ion etain Sn+

Oriented Sn⁺ ions in the (5s5p²)⁴P_{$\text{1}\text{2}$} level are produced by Penning collisions between Sn atoms in the ground state and optically oriented He (2³S₁) metastable atoms. If r.f. transitions are induced in the 2³S₁ He level, the circularly polarized light emitted by the ions in a direction perpendicular to the magnetic field is modulated at the r.f. frequency; the variation of the degree of modulation with the r.f. frequency allows a determination of the lifetime τ' of the ion level. The lifetime and the Landé g-factor of the Sn⁺ (⁴P_{$\text{1}\text{2}$}) level are also measured by direct magnetic resonance. The line shape is also computed when the resonances of the He atom and of the Sn⁺ ion overlap; the experimental signals are in good agreement with this computation.     

Electron spectroscopy using excited atoms and photons IV. Penning ionization of ethylene

Using helium metastable atoms (2¹S, 2³S), the Penning ionization of C₂H₄ has been studied using a high resolution electrostatic electron analyzer. The Franck—Condon envelope for the ground state of C₂H₄⁺ (X²B_3u) is found to be the same for He* (2³S) Penning ionization and 584 Å photoionization. The ΔE shift values and the relative electronic transition probabilities are reported for four ionic states. Unusually large differences have been found for the relative electronic transition probabilities for Penning ionization and photoionization.     

Etude de l'energie des electrons ejectes au cours de l'ionisation penning de l'hydrogene moleculaire par les etats metastables 21S et 23S de l'helium

The authors report experiments on the Penning ionization of molecular hydrogen by metastable helium (2¹S and 2³S states). The vibrational structure of the H₂⁺ ion in the state X²Σ_g⁺ is resolved. The relative population of the three first vibrational levels is obtained. The authors also show that a continuum is superposed on the Penning ionization due to the autoionization process.     

Interaction of trapped metastable excited He atoms with solid noble gases,Ne, Ar and Kr,investigated by EPR

Local metastable excited states are found in Ne, Ar and Kr cryocrystals as He gas-discharge products are trapped in the growing cryocrystals. These states are detected by EPR and are interpreted as being local metastable excitednp⁵(n+1)s³P₂ atomic-type states in Ne, Ar and Kr cryocrystals. Analysis of the results allows the following explanation of the observed effect to be given. For the Ne cryocrystal the effect is interpreted as a new phenomenon: quasi-resonance transfer of excitation energy from the metastable He 2³S₁ atom trapped in a growing neon cryocrystal to the exciton energy band of the neon crystal followed by the exciton self-trapping into the 2p⁵3p state and subsequent decay, ending in the 2p⁵3s³P₂ state recorded by EPR in our experiment. In the case of Ar and Kr cryocrystals the effect is explained as being due to an internal ionization of the cryocrystals by the excitation energy of trapped metastable He atoms, which implies the formation in the cryocrytal of a Rg⁺ ion and a free electron in the conduction band, whereupon the fast (of 10^?12 s) self-trapping reaction of a hole follows: Rg⁺+Rg→Rg ₂ ⁺ . Thereafter the dissociative recombination reaction Rg ₂ ⁺ +e→Rg ₂ ^** →Rg+Rg*(³P₂) could take place.     

Comparative study of He(23S)-penning ionization and He(I) photoionization of CF4, CCl4, and the chlorofluoromethanes by electron-ion coincidence spectroscopy

We present electron—ion coincidence spectra of the chlorofluoromethanes obtained after He(I)-photoionization and Penning ionization by He(2³S).Remarkable differences between both modes of ionization exist for CF₃Cl. Our tentative interpretation suggests the existence of a strongly bound interaction potential of ionic character between He(2³S) and CF₃Cl, in addition to the essentially flat covalent potential.     

Photoelectron spectra of F3SiC2H4Si(CH3)3 molecule using monochromatized synchrotron radiation

A variety of photoelectron spectra for gas phase F₃SiC₂H₄Si(CH₃)₃ molecule have been measured using monochromatized undulator radiation and a hemispherical electrostatic analyzer. Valence photoelectron spectrum shows many peaks for ionization from shallow and deep molecular orbitals in the binding energy region of 9–40 eV. A calculation of ionization energies using the outer valence Green's function method indicates energies in agreement with experimental results below 17.5 eV. Spectra for Si L-shell electron emission show chemical shifts of Si atoms induced from different chemical environments around two Si atoms and also exhibit spin–orbit splitting for 2p photoelectrons. Further photoelectron spectra for C K-shell and F K-shell are discussed in comparison with those of related molecules.     

The origin of K2, Rb2 and Cs2 triplet 13Πg−X3Σ+u bands in discharge

The absorption and emission spectra of potassium, rubidium and caesium low-pressure discharges have been studied at the far blue wings of resonance D2-lines. The observed diffuse bands were attributed to the 1³Π_g?X³Σ⁺_u transition. Experiments revealed the recombination ²P + ²S nature of these bands, and the corresponding rate coefficients were obtained. Energies of the higher excited states as well as the X³Σ⁺_u -state well depths for K₂, Rb₂ and Cs₂ molecules were estimated.     

O2的化学吸附对2H—MoS2(0001)清洁表面和离子溅射表面电子结构的影响

利用低能N⁺(0.5keV)离子轻微轰击2H-MoS₂(0001)清洁表面,从UPS(HeⅠ,HeⅡ)得到d电子峰向E_F移动,价带顶出现明显的“肩膀”或带尾,它随轰击时间的增加而增强,同时使d_(z²)带变宽。UPS的结果表明,这种表面在室温下有明显的O₂吸附活性,O₂吸附后这个肩膀明显下降。结合XPS,AES和LEED的研究,我们认为这个“肩膀”态与次表面原子层的Mo原子的d电子的暴露和最外表面原子层s原子空位缺陷的产生有关。这些新的表面电子态与加氢脱硫(HDS)催化活性中心有密切的关系。 关键词：     

On the photoelectron spectrum of CS2

High-resolution photoelectron spectra of CS₂ have been obtained by photoionization with the He(I) (58.4 nm), Ne(I) (73.58–74.37 nm) and Ar(I) (104.8–106.7 nm) resonance lines. The resolution of about 17 meV was further improved by deconvolution of the experimental data. The formation of the X?²Π_g and B?²Σ_u⁺ states is accompanied by a weak ν₂ excitation. The spin—orbit splitting of the òΠ_u state is completely resolved, and a value of 186 cm^?1 is reported. We confirm the value of 12.689 eV for the ionization threshold of the Ã²Π ^u3/2 state, and show that the small peak observed at lower energy is due to a hot band.     

Ejection of H2O,O2, H2 and H from water ice by 0.5–6 keV H+ and Ne+ ion bombardment

The ejection of H₂O, O₂, H₂ and H from water ice at 30–140 K, bombarded by 0.5–6 keV H⁺ and Ne⁺ was studied experimentally. Neon ions in this energy range deposit their energy in the ice by nuclear collisions, whereas with protons of 0.5 to 6 keV the energy deposition mechanism shifts gradually from predominantly nuclear collisions to predominantly electronic processes. The existing theory of nuclear sputtering predicts very well the yield of ejected water molecules and the experimental results in the region of electronic processes agree well with the experimental results of Lanzerotti, Brown and Johnson. However, the major mass loss from water by ion bombardment is via the ejection of O₂, H₂ and H atoms, which exceed the ejection of water molecules. O₂ and H₂ production is markedly enhanced at temperatures exceeding ~100 K, whereas H₂O and H production are temperature independent, suggesting that O₂ and H₂ are produced in the bulk of the ice whereas H₂O and H atoms are ejected from the surface or near surface layers.     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.     

The identification of two entrance channels in the reaction of metastable helium He(23S,21S) with SO2

The energy spectrum of electrons emitted in the reaction of He(2³S) and He(2¹S) with SO₂ indicates that in addition to the covalent entrance channel a strongly attractive ionic channel plays a role. We find upper limits for the well depth of the potential curve that corresponds to the latter channel of D_e ? 3.5 eV and D_e ? 4.3 eV for He(2³S) and He(2¹S) as the reaction partner, respectively. The partitioning between the two entrance channels can be understood by assuming the coupling matrix between both channels to depend strongly on the orientation of the SO₂ molecule with respect to the incident metastable He*.     

Excitation and quenching of ultraviolet nitrogen bands in the mixture of N2 and O2 molecules

Total quenching rate coefficients of three singlet and three triplet states of molecular nitrogen in the collisions with O₂ molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of N₂^? molecules are compared with the available experimental data. An influence of collisional processes on vibrational populations of electronically excited N₂(a¹Π_g) and N₂(A³Σ_u⁺) molecules is studied for conditions of laboratory discharge in N₂ and O₂ at admixtures of molecular oxygen 0%-20% for the pressures 1-1000 Pa. It is indicated that molecular collisions cause changes in relative populations of vibrational levels of these states and intensity relations of ultraviolet bands of N₂ with rise in the pressure and the O₂ admixture.