# Two- and many-body effects in cation emission from H 2 O molecules by O + impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

B. Sulik, Z. Juhasz, Elie Lattouf, J. A. Tanis, Bernd A. Huber, E. Bene, S Kovács, P. Herczku, A Méry, Jean-Christophe Poully, et al.

► To cite this version:

B. Sulik, Z. Juhasz, Elie Lattouf, J. A. Tanis, Bernd A. Huber, et al. Two- and many-body effects in cation emission from H 2 O molecules by O + impact at keV energies: Similarities between ionization of atoms and proton emission from molecules. Journal of Physics: Conference Series, 2015, XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015) 22–28 July 2015, Toledo, Spain, 635 (3), pp.032118. 10.1088/1742-6596/635/3/032118. hal-02894124

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# Two- and many-body effects in cation emission from H₂O molecules by O⁺ impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

To cite this article: B Sulik et al 2015 *J. Phys.: Conf. Ser.* **635** 032118

View the [article online](#) for updates and enhancements.

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# Two- and many-body effects in cation emission from H₂O molecules by O⁺ impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

To cite this article: B Sulik et al 2015 *J. Phys.: Conf. Ser.* **635** 032118

View the [article online](#) for updates and enhancements.

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# Two- and many-body effects in cation emission from H₂O molecules by O⁺ impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

B. Sulik*<fnref n="1" />, Z. Juhász*, E. Lattouf†, J. A. Tanis†,§, B. A. Huber†, E. Bene*, S. T. S. Kovács*, P. Herczku*, A. Méry†, J.-C. Poully†, J. Rangama†, and J.-Y. Chesnel†

* Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), H-4001 Debrecen, Hungary

† Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), 6 Bd Mar. Juin, F-14000 Caen, France

§ Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008 USA

**Synopsis** We demonstrate that energy and angle differential emission yields of fragment ions provide valuable information about the collisions of keV energy ions and molecules. For proton fragments, originating from larger molecules, there are striking similarities to the spectra of electrons emitted in fast ion-atom collisions.

The rich structure of the spectra of ejected electrons in fast ion-atom collision experiments provides deep insight into the details of the ionization process [1]. The key for clarity there is the large proton/electron mass ratio. Electrons move in the fields of much heavier centers.

Here we demonstrate that double differential emission yields of fragment ions provide similarly valuable information in ion-molecule collisions at keV energies. For protons emitted from heavier molecules, due to the large mass ratio, there are close similarities to ionization.

Figure 1 shows experimental double-differential cross sections (DDCS) for cation emission in 6.6-keV ¹⁶O⁺ + H₂O collisions. The experimental arrangement was identical with that of ref. [5]. The main component of each spectrum is a broad, slowly decreasing structure. There the relative contributions of H⁺ and heavier fragments were derived from complementary time-of-flight measurements. The low energy part is mostly due to many-body processes with small momentum transfer, in analogy with the dipole-ionization dominated low energy electron emission in fast ion-atom collisions [1]. At forward angles (less than 90°) pronounced peaks are observed at higher energies. These peaks are due to the different cations formed in hard binary collisions [2-5], similarly to electron emission. We note that the heavier oxygen ions are mostly recoils, appearing in the binary ridge, while proton emission is dominated by many-body effects, and it is almost isotropic at low energies. One should keep in mind that highly charged ion impact is somewhat different. There multiple charge-exchange processes, followed by Coulomb explosion, dominate the fragment ion spectra at low energies.

<figure><img src="image_4.png" /><figcaption>**Figure 1.** Full curves: Experimental DDCS for cation emission at various angles in 6.6-keV ¹⁶O⁺ + H₂O collisions; Full circles: H⁺ contribution from TOF measurements. Open diamonds: O⁺ and OH⁺ contributions from TOF; Each spectrum is multiplied by the indicated factor.</figcaption></figure>

This work was supported by the Hungarian National Science Foundation OTKA (Grant No. K109440), the French-Hungarian Cooperation Program PHC Balaton (No. 27860ZL/TéT_11-2-2012-0028), and the French-Hungarian CNRS-MTA Cooperation (ANION project).

## References

[1] N. Stolterfoht, R.D. DuBois and R. D. Rivarola, *Electron emission in heavy Ion Collisions* (Springer, Berlin, 1997, pp 1-16)

[2] Z. Juhász et al 2012 *J. Phys. Conf. Ser.* **388** 102051

[3] Z. Juhász et al 2013 *Phys. Rev. A* **87** 032718

[4] Z. Juhász et al 2014 *J. Phys. Conf. Ser.* **488** 102024

[5] E. Lattouf et al 2014 *Phys. Rev. A* **89** 062721

<footnote n="1">¹E-mail: sulik@atomki.mta.hu</footnote>
# Two- and many-body effects in cation emission from H₂O molecules by O⁺ impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

B. Sulik*<fnref n="1" />, Z. Juhász*, E. Lattouf†, J. A. Tanis†,§, B. A. Huber†, E. Bene*, S. T. S. Kovács*, P. Herczku*, A. Méry†, J.-C. Poully†, J. Rangama†, and J.-Y. Chesnel†

* Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), H-4001 Debrecen, Hungary

† Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), 6 Bd Mar. Juin, F-14000 Caen, France

§ Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008 USA

**Synopsis** We demonstrate that energy and angle differential emission yields of fragment ions provide valuable information about the collisions of keV energy ions and molecules. For proton fragments, originating from larger molecules, there are striking similarities to the spectra of electrons emitted in fast ion-atom collisions.

The rich structure of the spectra of ejected electrons in fast ion-atom collision experiments provides deep insight into the details of the ionization process [1]. The key for clarity there is the large proton/electron mass ratio. Electrons move in the fields of much heavier centers.

Here we demonstrate that double differential emission yields of fragment ions provide similarly valuable information in ion-molecule collisions at keV energies. For protons emitted from heavier molecules, due to the large mass ratio, there are close similarities to ionization.

Figure 1 shows experimental double-differential cross sections (DDCS) for cation emission in 6.6-keV ¹⁶O⁺ + H₂O collisions. The experimental arrangement was identical with that of ref. [5]. The main component of each spectrum is a broad, slowly decreasing structure. There the relative contributions of H⁺ and heavier fragments were derived from complementary time-of-flight measurements. The low energy part is mostly due to many-body processes with small momentum transfer, in analogy with the dipole-ionization dominated low energy electron emission in fast ion-atom collisions [1]. At forward angles (less than 90°) pronounced peaks are observed at higher energies. These peaks are due to the different cations formed in hard binary collisions [2-5], similarly to electron emission. We note that the heavier oxygen ions are mostly recoils, appearing in the binary ridge, while proton emission is dominated by many-body effects, and it is almost isotropic at low energies. One should keep in mind that highly charged ion impact is somewhat different. There multiple charge-exchange processes, followed by Coulomb explosion, dominate the fragment ion spectra at low energies.

<figure><img src="image_5.png" /><figcaption>**Figure 1.** Full curves: Experimental DDCS for cation emission at various angles in 6.6-keV ¹⁶O⁺ + H₂O collisions; Full circles: H⁺ contribution from TOF measurements. Open diamonds: O⁺ and OH⁺ contributions from TOF; Each spectrum is multiplied by the indicated factor.</figcaption></figure>

This work was supported by the Hungarian National Science Foundation OTKA (Grant No. K109440), the French-Hungarian Cooperation Program PHC Balaton (No. 27860ZL/TéT_11-2-2012-0028), and the French-Hungarian CNRS-MTA Cooperation (ANION project).

## References

[1] N. Stolterfoht, R.D. DuBois and R. D. Rivarola, *Electron emission in heavy Ion Collisions* (Springer, Berlin, 1997, pp 1-16)

[2] Z. Juhász et al 2012 *J. Phys. Conf. Ser.* **388** 102051

[3] Z. Juhász et al 2013 *Phys. Rev. A* **87** 032718

[4] Z. Juhász et al 2014 *J. Phys. Conf. Ser.* **488** 102024

[5] E. Lattouf et al 2014 *Phys. Rev. A* **89** 062721

<footnote n="1">¹E-mail: sulik@atomki.mta.hu</footnote>