1. Partial and differential electron impact ionization cross sections of acetylene S. Feil, K. Głuch, S. Matt, P. Scheier and T. Märk Institut für Ionenphysik Universität Innsbruck A-6020 Innsbruck LEIF – Meeting, Belfast 2003

2. Introduction Diploma thesis about: Physical and technological basics of Inductively coupled Vacuum Plasma Spraying (IVPS) At the Plansee Company in Reutte in Tirol Hochleistungswerkstoffe About me:

3. My job at Plansee I)Characterisation of the machine: I)Power measurements II)Temperatur measurements (in the spot) III)Particle velocity measurements IV)Flame temperature measurements II)Development of new warmstrenthened materials I)Re10W (mixed crystal hardening) II)Re3Hf (reference) III)Re3HfN(dispersion hardening) IV)Re3HfC(dispersion hardening) Hochleistungswerkstoffe

4. Mass spectrometry of molecules and clusters In April 2003 I started PhD. … on a double focussing mass spectrometer Work partially supported by the FWF, ÖAW and ÖNB, Wien, Austria. We also thank the European Commission, Brussels. …our group

5. Why C 2 H 2 ? Importance of electron collisional properties of acetylene for several reasons: edge plasmas in fusion reactors (wall-plasma-interaction) present in planetary and cometary atmospheres concentration of C 2 H 2 in the atmosphere of earth is expected to nearly double by the year 2030 due to the increased use of automobiles C 2 H 2 is a very simple molecule among hydrocarbons radiation chemistry ………

6. What was done?  Partial cross sections for electron impact ionization of C 2 H 2 were measured from threshold to 900eV  Ion kinetic energy distributions were deduced applying a deflection field method  Determination of cross sections that are differential with respect to the initial energy of the ion  Considering discrimination highly energetic fragment ions could be measured with a double focussing mass spectrometer in good agreement to specially dedicated instruments

7. Our apparatus Two sector field MS: NIER Type ion source deflector plates y z x B-fieldE-field electron beam detector Discrepancies in the literature for cross sections of fragment ions Specially dedicated instruments Correction of data due to kinetic energy effects a) integration of beam profile b) determination of discrimination in the ion source

8. Technique for E kin determination Measurement: z – profile What is a z – profile? electron beam deflector plates

9. Work schedule Smoothing (with gauss) then differentiate  distribution function E kin = c×U z 2 c from parent ions Include discrimination Measurement z - profile Data analysis Experiment

10. Example: CH + out of C 2 H 2 Ion beam profile: splits the molecule C 2 H 2 + e  CH + + CH + 2e But: C 2 H 2 + e  C 2 H 2 ++ + 3e same m/q ratio

11. Mass spectrum of C 2 H 2  More than 50% of m/q ratio 13 is C 2 H 2 ++

12. Example: CH + out of C 2 H 2 Measurement and gauss- smoothed curve Differentiated, squared and rescaled

13. Example: CH + out of C 2 H 2 Corrected due to the discrimination Doing this analysis and finally integrate the kinetic energy distribution One can get partial cross sections of ions but with more information

14. Final result: CH + out of C 2 H 2 One can see the 3 different reaction channels dependent on the electron energy Partial cross section CH + & C 2 H 2 ++

15. Identification of different channels Compare the red process with the ionization energy of C 2 H 2 ++ : Appearance of this reaction channel at ~ 36eV Partial cross section CH + & C 2 H 2 ++

16. Ionization Energy of C 2 H 2 ++ One can deduce that the second (red) process comes purely from the doubly charged acetylene

17. C 2 H 2 ++ can`t be neglected ! Stability of this di-cation?  check a decay reaction of C 2 H 2 ++ (with MIKE technique)

18. Further investigations ( C 2 H 2 ++  C 2 H + + H + ) … with MIKE scan technique(m 1  m 2 + m 3 ) Mass analysed Ion Kinetic Energy y z x B-fieldE-field electron beam detector Selecting a mass Scanning the electric sector Identification:

19. Further investigations ( C 2 H 2 ++  C 2 H + + H + ) The kinetic energy of C 2 H + is then ~ 150meV. The fragment C 2 H + at E frag * = 982.7V = 3.88eV

20. Conclusion it is possible to determine partial cross sections in good agreement with results obtained by using specially dedicated instruments The doubly charged fraction in the mass spectrum of C 2 H 2 can`t be neglected With the present method it is possible to identify the different channels of the reaction processes The cross section of CH + could be deduced by subtracting the „red process“ from the partial cross section

22. Final result: H + out of C 2 H 2 One can see the 2 different reaction channels dependent on the electron energy

23. H + out of C 2 H 2

24. The NIER – Type source

25. Example: CH + out of C 2 H 2 Measurement and gauss- smoothed curve Differentiated, squared and rescaled

26. Example: CH + out of C 2 H 2 Corrected due to the discrimination function Doing this analysis with different electron energies and finally summing all graphs up One can get partial cross sections of ions but with more information