Superelastic Collisions of Vibrationally Excited<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow /><mml:mrow /><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mprescripts /></mml:mmultiscripts></mml:mrow></mml:math>with Atoms and Molecules

Herrero, F. A.; Doering, J. P.

doi:10.1103/physrevlett.29.609

Cited by 14 publications

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“…Due to the high anharmonicity of H 2 + (X 1 Σ g + ) the position of peak I** moves to a lower energy loss than predicted, solely on the basis of de-excitation from υ" = 1 to υ' = 0. Peak II is due to vibrational deexcitation of H 2 + , except ∆υ = -2, which has a considerably lower transition probability than ∆υ = -1 37 .…”

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“…Energy resolution of ഠ 0.1-0.2 eV (FWHM) was obtained in energy loss (and superelastic) spectra. They studied pure vibrational transitions of H + and H 2 + impacting on molecular targets 37 and also optically forbidden transitions in the TES spectra of substituted ethylenes by H + and He + impact. 38 This design of translational energy loss spectrometer, utilizing retardation to low energy prior to energy analysis, is one of the commonest choices of TES instrumentation.…”

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The design and performance of a high resolution translational energy loss spectrometer

Brenton

Lock

1997

Rapid Commun. Mass Spectrom.

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An instrumental development is described that achieved high energy resolving power when studying collisions between fast ion beams, at keV energies, interacting with thermal molecular and atomic gaseous targets. This technique is referred to as translational energy spectroscopy (TES) and can reveal spectroscopic information on the states of the participating species, the dynamics of the collision, lifetimes of species formed, state-to-state collision cross-sections and populations of states. The instruments described are based on an unique symmetrical arrangement of cylindrical electrostatic analysers. These are placed in a double focusing ion-optical geometry leading to very small first and second order image aberrations, sufficient to obtain a primary energy resolving power of 10 5 . Two such instruments were developed and their relative performances are compared experimentally and through computer modelling; the second, and larger, instrument has an improved sensitivity by an order of magnitude and a three times increase in resolving power. This has enabled collision spectroscopy to achieve performance similar to electron energy-loss spectroscopy and photoelectron spectroscopy, with a resolution on the unscattered ion beam measured to be 0.01 eV, at 3 keV collision energy, on energy loss processes of ≥ 0.03 eV. These developments allow TES to observe, (i) the vibrational/electronic spectroscopy of keV ion/molecule collisions; (ii) spin-selective spectra; (iii) the highly excited states close to and beyond the ionization limit of the target species; and (iv) involatile targets using a high temperature cell. The validity of optical quantum selection rules, relying on the electric-dipole interaction governing photon-induced transitions, has been tested for TES, which relies on the more general ion/neutral interaction potential responsible for collisional excitation. Spin conservation was found to be strongly adhered to, whilst orbital angular momentum and total angular momentum were not. The specific selection rules for homonuclear diatomics g < -> g and u < -> u were found to be allowed in TES, in contradiction to the case of optical spectroscopy, whilst there was some preliminary evidence that the optical Σ + -Σ -symmetry-forbidden transition was also forbidden for the TES reactions studied. For H 2 + projectiles, excitation to triplet states is strongly favoured over excitation to singlet states.

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The design and performance of a high resolution translational energy loss spectrometer

Brenton

Lock

1997

Rapid Commun. Mass Spectrom.

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“…In view of the attractive simplicity of the alkali ionhydrogen molecule systems, and in response .to certain apparent differences in the behavior of the Li+ -Hz and K+ -Dz systems as initially repoited~lZ,l 6 we undert~ok the scattering of Na+ by Dz at large angles using an experimental technique 1 lt h e repor our exper1men a resu s ere, and interpret ~hem in terms of a model which is significantly different from those which have been employed in the past.…”

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Large angle inelastic scattering of Na+ by D2

Dimpfl

Mahan

1974

The Journal of Chemical Physics

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We report measurements of the· inelasticity of the large angle scattering of Na+ by Dz, HD, and Hz in the initial relative energy range 0. 74 -16.9 eV. The interpretation of the vibrational inelasticity leads to the conclusion that perpendicular (C 2 v) rather than collinear + ,,.conformations of the Na -n 2 system produce the most intense inelastic scattering. The results of exact clas··sical trajectory calculations ivhich elucidate t:h~ effects of oscillator orientation and internal potential function on the inelasticity of collisions are presented.By fitting the calculated inelasticities to the experimental data, we have deduced both the energy and length parameters of a two term exponential repulsive potential·for this system. Oz -Ar, 0 -o 2 , and CO -Ar system~. In these studies, the excitation to individual vibrational levels was resolved, and the angular and energy dependence of the inelastic collision probability determined.The alkali metal ions in collision with Hz, Dz, and HD should.be parti~ularly informative systems for the study of of Na + from Hz and Dz were published in a second paper. 13 Vart Dop, Boerboom, and Los 14 , 15 also have studied the scattering of K+ from Hz and Dz, with particular emphasis on higher relative energies. Toennies and coworkers 16 -18 The energy selector was operated at a resolution of 3% of the energy of the beam in the selector. The transmission of the selector was satisfactory when the ion energy in the selector was 4 eV or greater. Focusing requir~ments connected with the subsequent acceleration of the·energy selected ions made it impractical to pass the ions through the energy selector at less than 10% of their final laboratory energy in the scattering region. Thus the laboratory energy spread of the tinscattered beam was never less th~n 0.12 eV FWHM.After leaving the energy selector, the ion beam was accelerated and focused into the scattering cell by a three element aperture lens designed by using the results of Imhof and Read. 21 .The scattering cell has fixed entrance and exit apertures, so only scattering at 0° ± 1. 0° in the laboratory is observed. The cell was machined from stainless steel and 5 was enclosed by a liquid nitiog~n cooled copper jacket. The oper~ting temperature of the cell was -177°C, which considerably decreased the lbss in resolutiori which results from the thermal motion of the scattering gas.The energy distribution of the ions leaving the scattering cell was measured with an electrostatic energy analyser which was in large measure identical to the ion energy selector. In ]Daking a scan of the energy spectrum of the scattered ions, a '• thre~ element aperture lens was used to actelerate or decelerate ion~ to a fixed kinetic energy which was passe~ by the energy analyser. The ions which had been scattered through 180° in the center-of~mass coordinate system were of primary interest, and had lower kinetic energy in the laboratory than the unscattered beam. In early experiments, observation of the back- Table I as a function of t...

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“…In view of the attractive simplicity of the alkali ionhydrogen molecule systems, and in response .to certain apparent differences in the behavior of the Li+ -Hz and K+ -Dz systems as initially repoited~lZ,l 6 we undert~ok the scattering of Na+ by Dz at large angles using an experimental technique and are expected to produce the greatest vibrational inelasticity .,in <i. syst_en~ where the attractive part of the intermolecqla~ potential f~weak.…”

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Large angle inelastic scattering of Na+ by D2

1975

Vacuum

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We report measurements of the· inelasticity of the large angle scattering of Na+ by Dz, HD, and Hz in the initial relative energy range 0. 74 -16.9 eV. The interpretation of the vibrational inelasticity leads to the conclusion that perpendicular (C 2 v) rather than collinear + ,,.conformations of the Na -n 2 system produce the most intense inelastic scattering. The results of exact clas··sical trajectory calculations ivhich elucidate t:h~ effects of oscillator orientation and internal potential function on the inelasticity of collisions are presented.By fitting the calculated inelasticities to the experimental data, we have deduced both the energy and length parameters of a two term exponential repulsive potential·for this system. Oz -Ar, 0 -o 2 , and CO -Ar system~. In these studies, the excitation to individual vibrational levels was resolved, and the angular and energy dependence of the inelastic collision probability determined.The alkali metal ions in collision with Hz, Dz, and HD should.be parti~ularly informative systems for the study of of Na + from Hz and Dz were published in a second paper. and HD as target molecules, and the results of these are also included in Table I. Because of the effe~ts of increased target gas motion, poorer resolution in the barycentric system, and the absence. of a convenient target gas to calibrate th~ energy scale accurately, the results from these last two sy~tems were s6mewhat"+ less sati~factory than those from the· Na -n 2 experiments.In Fig. 2, we show examples of the energy ·spectra of + Na scattered from n 2 at two different initial relative energies.For cbmparison, the corr~sponding elastic scattering of Na+ from He is shown. At the lower initial relative energy of 11.8 eV, Na+ recoiling from n 2 has its intensity maximum at a laboratory energy slightly greater than the position which corresp6nds to elastic scattering~ Since higher laboratory energies correspond to inelastic scattering in this angular region, the maximum in the curve corresponds to a relatively small inelasticity, 1.1 eV.In addition, comparison o£ the scattering of Na+ from n 2 with that from He shows that in the former case there is very significant broadening of the peak in the direction of inelastic scattering.The inelastic scattering of Na+ from n 2 is more evident in the data ~aken at the higher relatiVe energy of 16.30 eV, as 8 is shown in Fig. 2a. Here both th~~di~placement of the intensity maximum from the value expected for elastic scattering and the asymmetric broadening in the direction of inelastic scattering are quite pronounced. As the initial relative energy is increased still further, both these features become more obvious.It should be noted that there is a small amount of asymmetric broadening of the distribution of The model also leads us to a preferabie means of interpreting our experimental data.As is well-known, 2 a the relative kinetic energy T of a collinear iriatomic system can b~ writteri in the diagonalized fqrm where the coordinates X and Y are related to the inte...

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Superelastic Collisions of Vibrationally ExcitedH2+with Atoms and Molecules

Cited by 14 publications

References 5 publications

The design and performance of a high resolution translational energy loss spectrometer

The design and performance of a high resolution translational energy loss spectrometer

Large angle inelastic scattering of Na+ by D2

Large angle inelastic scattering of Na+ by D2

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