Showing papers on "Reionization published in 1986"
01 Apr 1986-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: For surfaces with a work function as large as 4 eV, the resonance ionization of incident He ∗ occurs with a probability close to unity; for surfaces with small work functions, the probability of resonance ionisation is small as discussed by the authors.
Abstract: In the scattering of He + with a low energy of order 1 keV at solid surfaces, not only neutralization of He + but also reionization of neutralized He 0 is important. The reionization occurs in the step of the collision with a particular surface atom by an electron promotion mechanism. The neutralization of He + before and after the reionization is mainly caused by an Auger process provided that the work function of the target surface is larger than about 4 eV. For surfaces with a work function as large as about 4 eV, the resonance ionization of incident He ∗ occurs with a probability close to unity; for surfaces with a work function as small as about 2 eV, the probability of the resonance ionization is small. An inelastic energy loss attributable to excitation in target atoms decreases as the number of empty valence states of the target atoms decreases.
99 citations
73 citations
TL;DR: The reionization mechanism of neutralized helium in low-energy ion-scattering spectroscopy is clarified on the basis of ab initio Hartree-Fock self-consistent-field calculations for fifteen diatomic systems.
Abstract: The reionization mechanism of neutralized helium in low-energy ion-scattering spectroscopy is clarified on the basis of ab initio Hartree-Fock self-consistent-field calculations for fifteen diatomic systems. Reionization is explained by level crossings of the He 1s level with open valence levels of the target, which is caused by the antibonding interaction of the He 1s level with the target core levels. Calculated threshold energies for reionization are qualitatively in good agreement with those observed in the experiments.
61 citations
TL;DR: It appears that theory overestimates the heat-of-formation values for such hypervalent neutral species as H2CYH'+ or H,CY'+ from partial or complete isomerization of H,CCI to the more stable isomer H3CY.
Abstract: Contrary to the predictions of ab initio theory, the neutral ylides H2CC1H (l) , H,CFH, and H2COH2, as well as H,CNH3, exist in local energy minima. These have been prepared for study from fast gaseous H2CYH'+ ions by neutralization with Hg vapor. Reionization of the resulting fast neutrals produces abundant molecular ions, which could represent H2CYH'+ or H,CY'+ from partial or complete isomerization of H2CYH to the more stable isomer H3CY. However, increasing the pressure of the reionizing collision gas (0, or He) increases the relative abundance of YH dissociation products, such as HCI from 1, which must originate from H,CYH, not H3CY. Thus an appreciable fraction of each of these neutral ylides must have survived for the microsecond lifetime of the experiment. For 1 this was confirmed by reionization to H2CC1H2+, which shows a significantly different fragmentation pattern from that obtained from H3CCI. More than half of 1 molecules formed by vertical neutralization are still undissociated after s, and of these less than half have isomerized to H,CCI. I t appears that theory overestimates the heat-of-formation values for such hypervalent neutral species. Ylides are widely utilized as intermediates in organic synthesis.] For these hypervalent species stable forms such as certain iodonium ylides (R2C--I+R R2C=IR) are rare,, so that most characterizations of the structure and energetics of the simplest ylides H2CYH have been based on molecular orbital theory., In contrast, the ionized forms of many such simple ylides are actually more stable thermodynamically than their conventional isomers (e.g., 'CH20+H2 vs. H3COH'+); theoretical and experimental ( 1 ) Johnson, A. W. Ylid Chemistry: Academic Press: New York, 1966. Morris, D. G. In Suruey of Progress in Chemistry: Wubbels, G. G., Ed.: Academic Press: New York, 1983, pp 189-257. (2) Moriarty, R. M.; Bailey, B. R., 111; Prakash, 0.; Prakash, 1. J . Am. Chem. SOC. 1985, 107, 1375-1378. Olah, G. A,; Doggweiler, H.: Felberg, J . D. Ibid. 1985, 107, 4975-4978. Turro, N. J.; Cha, Y.; Gould, I. R.: Padwa, A.; Gasdaska, J. R.; Tomas, M. J. Org. Chem. 1985,50,4417-4418. For the definition of hypervalency, see: Schleyer, P. v. R. In New Horizons in Quanrum Chemistry; Lowdin, P.-O., Pullman, B., Eds.; Reidel: Dordrecht, (3) (a) Lischka, H. J . Am. Chem. SOC. 1977, 99,353-360. (b) Eades, R. A.; Gassman, P. G.; Dixon, D. A. Ibid. 1981, 103, 1066-1068. (c) Pople, J . A,: Raghavachari, K.; Frisch, M . J . ; Binkley, J. S.; Schleyer, P. v. R. Ibid. 1983, 105, 6389-6398. (d) Dixon, D. A,; Dunning, T. H.; Eades, R. A,; Gassman, P. G. Ibid. 1983, 10.5, 701 1-7017. (e) Harding, L. B.; Schlegel, H. B.: Krishnan, R.; Pople, J. A. J . Phys. Chem. 1980.84, 3394-3401. (0 Mitchell, D. J.; Wolfe, S.; Schlegel, H. B. Can. J . Chem. 1981, 59, 3280-3292. (g) Yates, B. F.; Bouma, W. J.; Radom, L. J . Am. Chem. SOC. 1984, 106, 5805-5808. 1983; pp 95-107. 0002-7863/86/ 1508-5847$0 1.50/0 studies show that the ionic isomers are usually separated by high isomerization barrier^.^ Here we use n e u t r a l i z a t i ~ n ~ ~ ~ of the appropriate ylide ions to prepare several simple gaseous ylides (Y = CI, 1; F, 2; OH, 3; NH,, 4), studying these by collisionally activated dissociation (CAD) and rei~nizat ion.~ (4) (a) Radom, L.; Bouma, W. J.; Nobes, R. H.; Yates, B. F. Pure Appl. Chem. 1984.56, 1831-1842. (b) Schwarz, H. MassSpecrrosc. (Tokyo) 1984, 32, 3-16. (c) Terlouw, J. K.; Heerma, W.; Dijkstra, G.; Holmes, J . L.; Burgers, P. C. Int. J . Mass Spectrom. Ion Phys. 1983, 47, 147-150. (d) Maquin, F.; Stahl, D.; Sawaryn, A,; Schleyer, P. v. R.: Koch, W.: Frenking, G.; Schwarz, H. J . Chem. Soc., Chem. Commun. 1984, 504-506. ( 5 ) (a) McLafferty, F. W.: Todd, P. J.: McGilvery. D. C.: Baldwin, M. A. J . Am. Chem. Soc. 1980, 102, 3360-3363. (b) Danis, P. 0.: Wesdemiotis, C.: McLafferty, F. W . Ibid. 1983, 105, 7454-7456. (c) Burgers, P. C.: Holmes, J. L.; Mommers, A. A,; Terlouw, J. K. Chem. Phys. Let!. 1983, 102, 1-3. (d) Wesdemiotis, C.; Danis, P. 0.: Feng, R.; Tso, J.; McLafferty, F. W. J . Am. Chem. SOC. 1985, 107, 8059-8066. (e) Terlouw, J. K.: Kieskamp, W. M.; Holmes, J . L.; Mommers, A. A,; Burgers, P. C. Int. J . Mass Specrrom. Ion Processes 1985, 64, 245-250. (f) Danis, P. 0.; Feng, R.; McLafferty, F. W. Anal. Chem. 1986, 58, 348-354. (g) Danis, P. 0.; Feng, R.: McLafferty, F. W. Ibid. 1986, 58, 355-358. (h ) Wesdemiotis, C.; Feng, R.; Williams, E. R.: McLafferty. F. W. Org. Mass Specrrom., in press. (6) (a) Williams, B. W.; Porter, R. F. J . Chem. Phys. 1980, 73, 5598-5604. (b) Cleary, D. A.; Gellene, G. I.; Porter, R . F.: Burkhardt, C. E.; Leventhal, J . J . Ibid. 1982, 77, 1354-1361. (c) Gellene, G. 1.; Porter, R. F. Arc. Chem. Res. 1983, 16, 200-207. (d) Moran, T. F. In Electron-Molecule Interactions and Their Applications: Academic Press: New York, 1984; Vol. 2, pp 1-64.
53 citations
TL;DR: In this article, the neutralization-reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions.
Abstract: The neutralization-reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions. Ionic isomers that are indistinguishable by collisionally-activated dissociation because of easy interconversion can be characterized by neutralization-reionization if the corresponding neutrals show different reactivities, as is demonstrated for the [C2H5]+/C2H5˙ system and for [C2H4O2]+˙ isomers. For identification of mixtures of more than one neutral species, the relative efficiency for reionizing each neutral must be determined; e.g. the O2 reionization efficiency of ˙CH2OH radicals is ∼4 times greater than that of CH3O˙. This information and reference reionization spectra of CH3O˙ and ˙CH2OH show that metastable or collisionally activated methyl acetate cations lose CH3O˙, not ˙CH2OH as previously reported; the newly-formed CH3O˙ undergoes partial (∼20%) isomerization to ˙CH2OH in the ∼10−6s before reionization. Similar results are obtained for [B(OCH3)3]+˙.
53 citations
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TL;DR: In this article, the evolution of density perturbations in a two-component universe composed of neutrinos and dissipative gas on a spherically-symmetric model has been studied.
Abstract: The recent discovery of the large ‘honeycomb’ structure of the Universe has triggered many models of the Universe dominated by dark matter. The neutrino-dominated universe is a favorable model for explaining the size of the large-scale structure and the dark matter of the larger scale than the galactic one. Our calculations on the evolution of density perturbations in a two-component universe composed of neutrinos and dissipative gas on a spherically-symmetric model have shown that the galactic scale does correlate the scale of a void of galaxies: if a neutrino has the mass of some tens eV, galaxies of the typical size form surrounding a typical void.
3 citations