Measurements Of Kinetic Energy Distributions Research Articles

Mechanistic Insight into Gas Cluster-Induced Sputtering of Kilodalton Molecules Using Kinetic Energy Distribution Measurements

Recent progress in organic secondary ion mass spectrometry (SIMS) relied essentially on the development of new cluster beams, especially large atomic and molecular clusters formed via the adiabatic...

Exploring the dynamics of reaction N(2D)+C2H4 with crossed molecular-beam experiments and quantum-chemical calculations

We conducted the title reaction using a crossed molecular-beam apparatus, quantum-chemical calculations, and RRKM calculations. Synchrotron radiation from an undulator served to ionize selectively reaction products by advantage of negligibly small dissociative ionization. We observed two products with gross formula C(2)H(3)N and C(2)H(2)N associated with loss of one and two hydrogen atoms, respectively. Measurements of kinetic-energy distributions, angular distributions, low-resolution photoionization spectra, and branching ratios of the two products were carried out. Furthermore, we evaluated total branching ratios of various exit channels using RRKM calculations based on the potential-energy surface of reaction N((2)D)+C(2)H(4) established with the method CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p)]. The combination of experimental and computational results allows us to reveal the reaction dynamics. The N((2)D) atom adds to the C=C π-bond of ethene (C(2)H(4)) to form a cyclic complex c-CH(2)(N)CH(2) that directly ejects a hydrogen atom or rearranges to other intermediates followed by elimination of a hydrogen atom to produce C(2)H(3)N; c-CH(2)(N)CH+H is the dominant product channel. Subsequently, most C(2)H(3)N radicals, notably c-CH(2)(N)CH, further decompose to CH(2)CN+H. This work provides results and explanations different from the previous work of Balucani et al. [J. Phys. Chem. A, 2000, 104, 5655], indicating that selective photoionization with synchrotron radiation as an ionization source is a good choice in chemical dynamics research.

シングルバンチ放射光とミニチュア円筒鏡型分析器（ＣＭＡ）を用いた脱離イオンの質量と運動エネルギー分布の同時測定―凝縮ＮＨ３の内殻励起誘起Ｈ｀＋´脱離研究への応用―

We measured mass and kinetic-energy distribution of desorbed ions using a miniature cylindrical mirror analyzer (CMA) and synchrotron radiation under the single-bunch mode operation. We have applied it for the measurements of kinetic energy distribution of ions desorbed by N 1s transitions of condensed NH3.

Desorption of water cluster ions from the surface of solid rare gases

Electron or photon irradiation of H2O adsorbed on the surface of rare gas solids induces the desorption of protonated water clusters, (H2O)nH+. The yield and the size n distribution of cluster ions depend on the coverage, the deposition temperature of the water, and the thickness of the rare gas film. These results indicate that the (H2O)nH+ ions originate from the isolated water clusters, and the most important factor determining the size n distribution of desorbed (H2O)nH+ is the sizes of water islands on the rare gas solid. The measurement of kinetic energy distributions indicated that the desorbing energy of clusters depend on the rare gas species of the substrates and the cluster size. It is suggested that the (H2O)nH+ desorption is due to Coulomb repulsion between the ionic water cluster and the rare gas ion.

X-ray initiated molecular photochemistry of Cl-containing adsorbates on a Si(1 0 0) surface using synchrotron radiation

X-ray initiated molecular photochemistry for SiCl 4 and CCl 4 adsorbed on Si(1 0 0) at ∼90 K following Cl 2p core-level excitation is investigated by photon stimulated ion desorption and ion kinetic energy distribution measurements. The Cl 2 p → 8 a 1 ∗ excitation of solid SiCl 4 induces the significant enhancement (∼900%) of the Cl + yield, while the Cl 2 p → 7 a 1 ∗ excitation of condensed CCl 4 leads to a moderate enhancement (∼500%) of the Cl + yield. The enhancement of Cl + yield at the specific core-excited states is strongly correlated to the ion escaped energy. Upon X-ray exposure for CCl 4 adsorbed on Si(1 0 0) (20-L exposure), the Cl + yields at 7 a 1 ∗ resonances decrease and new structures at higher photon energies are observed. Cl + yields at these new resonances are significantly enhanced compared to those at other resonances. These changes are the results of desorption and surface reaction of the CCl 4–Si surface complex due to X-ray irradiation. We have demonstrated that state-specific enhancement of ion desorption can be successfully applied to characterize the reaction dynamics of adsorbates adsorbed on surfaces by X-ray irradiation.

Kinetic energy distribution of H + desorbed by core-level excitations of condensed ammonia using a miniature cylindrical mirror analyzer (CMA)

We have developed a miniature cylindrical mirror analyzer (CMA) mounted on a 70-mm-diameter conflat flange for measurements of kinetic energy distribution of ions desorbed in the polar angles of 24°–28° from the surface normal. The acceptance solid angle is 0.16 sr and the energy resolution (FWHM) is estimated as E/Δ E = 20. We have applied it for measurements of kinetic energy distributions of ions desorbed from condensed ammonia (NH 3) at the surface 4a 1 ← N 1s resonant transition ( hν = 400.7 eV) and at N 1s ionization ( hν = 412.5 eV). The results support the two H + desorption mechanisms proposed previously, that is, a four-step mechanism involving ultrafast H 2N–H extension within the lifetime of the N 1s core hole at 4a 1 ← N 1s, and a normal Auger stimulated ion desorption mechanism at N 1s ionization.

ミニチュア円筒鏡型分析器（ＣＭＡ）を用いた脱離イオンの運動エネルギー分布測定―凝縮Ｈ２Ｏの内殻励起誘起Ｈ｀＋´脱離研究への応用―

We have developed a miniature cylindrical mirror analyzer (CMA) for ion kinetic energy measurements. The CMA consists of a shield for electric field, inner and outer cylinders, a pinhole, and microchannel plates. We have applied it for the measurements of kinetic energy distribution of H+ desorbed by O 1s transitions of condensed H2O.

Stimulated desorption of D− from diamond: surface versus sub-surface processes via resonance dissociative electron attachment

In this work, we report on a study of low-energy electron stimulated desorption (ESD) of D− from in situ hot filament deuterated surfaces of diamond films. This deuteration procedure ensures that deuterium is predominantly adsorbed onto the diamond surface and no significant diffusion underneath the surface takes place. The cross-section for D− ESD through dissociative electron attachment (DEA) obtains a maximum value at ∼9 eV, whereas the dipolar dissociation process displays a threshold ∼14 eV. The ion kinetic energy distribution (KED) measurements show that in the DEA regime, desorption results in a narrow peak. To study the effect of inelastic interactions between the desorbing D− ions and the surface, in the DEA regime, KED measurements were performed as a function of desorbing angle with respect to the surface normal. It was found that with increasing angle from the surface normal, the D− KED broadens and its lower energy component increases in intensity. Our results show that low-energy ESD in the DEA regime may be applied to determine the presence of surface vs. sub-surface hydrogen (deuterium) in diamond.

Mechanisms and dynamics of electron-stimulated desorption ofD−from deuterated diamond surfaces: Surface versus subsurface stimulated desorption

In this work we report on a study of low-energy electron-stimulated desorption (ESD) of ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ from in situ hot-filament-deuterated surfaces of diamond films. This deuteration procedure ensures that deuterium is predominantly adsorbed on the diamond surface and that no significant diffusion underneath the surface takes place. For incident electron energies in the 5--35-eV range, dissociative electron attachment (DEA) and dipolar dissociation (DD) processes occur. The cross section for ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ ESD obtains a maximum value at \ensuremath{\sim}8 eV, whereas the DD process displays a threshold at \ensuremath{\sim}14 eV. Ion kinetic-energy distribution (KED) measurements show that in the DEA regime desorption results in a narrow peak whose energy position increases with the incident electron energy to a value that corresponds, minus a multiphonon excitation factor, to the thermodynamic limit, in agreement with gas-phase considerations. In the DD regime the ion KED displays a peak at \ensuremath{\sim}2 eV which does not depend on the incident electron kinetic energy. To study the effect of inelastic interactions between the desorbing ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ ions and the surface, in the DEA regime, KED measurements were performed as a function of desorbing angle with respect to the surface normal. It was found that with an increasing angle from the surface normal the ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ KED broadens, and its lower-energy component increases in intensity. These results clearly show that inelastic interaction between the outgoing ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ and the solid surface takes place, and determines the KED of desorbing ions. The ESD results obtained for the in situ deuterated surface are compared with those previously obtained for deuterated diamond films that contain some subsurface deuterium for which broad KED's were measured. A difference in the ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ KED in the DD regime is also measured. The indirect DEA process observed in the case of hydrogenated (deuterated) diamond films is strongly reduced in the present case of an on-top deuterated diamond surface. Our results show that ESD may be used to determine the presence of surface versus subsurface hydrogen (deuterium) adsorbed on diamond.

Kinetic energy measurements of molecular ions ejected into an electric field by matrix‐assisted laser desorption

Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix-assisted laser desorption are reported. The measurements were made in a time-of-flight mass spectrometer with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied to the mirror. The molecular ions were found to have less kinetic energy than the extraction field alone would normally provide, i.e., we observed an energy deficit. Under conditions typical for a matrix-assisted laser desorption experiment, the deficit is about 24 eV for molecular ions of insulin. The size of the deficit increases with the intensity of the molecular ion signal, and the molecular weight of the protein; it is also larger for negative molecular ions than for positive molecular ions.

Ion kinetic energy measurements on laser-induced plasmas in laser microprobe mass analysis (LAMMA). Part I. Methodology

A method for the measurement of kinetic energy distributions of ions produced in a laser microprobe mass spectrometer employing the energy cut-off property of an ion reflector has been developed. The method is insensitive to time of ion formation and to miscalibration of the flight-time equation, but requires accumulation of many spectra from uniform samples. When applied to elemental carbon foil, measurement of ion kinetic energy reveals that ionic species occur with different kinetic energy distributions. A substantial fraction of the ions having less kinetic energy than the full acceleration energy was observed.