Department of Experimental Physics, Comenius University Bratislava, Slovakia Formation of positive ions by electron impact: Temperature effects Š. Matejčík

Department of Experimental Physics Division of plasma physics low temperature plasma low temperature plasma technological plasmas, glow discharges... high pressure discharges high pressure discharges corona discharge, barrier discharge... reactions in the plasma reactions in the plasma electron impact ionization, electron attachment to the molecules...

Electron interactions Electron interactions Photon induced reactions Photon induced reactions Ion – molecule reactions Ion – molecule reactions Neutral reaction Neutral reaction Reactions on the surfaces Reactions on the surfaces Reactions in plasma

Electron impact ionization Electron impact ionization Electron attachment Electron attachment Excitation Excitation Dissociation Dissociation Electron reaction on the surfaces Electron reaction on the surfaces Electron interactions in plasma

Comenius university Electron attachment Electron attachment Electron impact ionization Electron impact ionization Electron induced reactions on surfaces Electron induced reactions on surfaces Preparation Electron impact excitation Electron impact excitation

Electron impact ionization: e + AB → AB + + 2e Dissociative electron impact ionization: e + AB → A + + B + 2e Ion pair formation: e + AB → A + + B- + e Fusion related research Molecules: CH 4, CH 3 D, CD 4, C 2 H 6, C 3 H 8

We have studied - appearance energies (AE) of the positive ions - gas temperature effects on the AE - isotopic effects on AE Theory: Ionization energies (OVGF, CCSD(T)) Appearance energies (G3, G3B3 and CBS-APNO, CBS-Q)

Experimental setup: E = 0 – 150 eV FWHM ~ meV Ie~20-100nA T = 293K 693K 693K

low T g high T g Electron impact ionization E σ

low T g Rate coefficient E σ f(E,T e ) high T g

A A+A+ IE VIE AIE AE

AE 1 AE 2 E f ΔAE = AE 2 -AE 1 = = E i (T 2 )-E i (T 1 ) E i (T)=E v (T)+E r (T)

σ E Sensitivity in present experiment: σ ~ m 2

Problem of threshold energy estimation

Atoms: Wannier theory:  w (E,AE,A,d) = 0 E<AE A(E-IE) d E>AE d=1.127 Threshold behaviour of the cross sections for EII f(E,U) - EEDF Fitting function:  w (E,AE,A,d)

d=1.127±0.01 Threshold behaviour of the cross sections

Molecules - empirical formula:  w (E,AE 1,AE 2,d1,d2A) = 0E<AE 1 A(E-AE 1 ) d1 E>AE 1 Threshold behaviour of the cross sections for EII A(E-AE 2 ) d2 + A(E-AE 1 ) d1 E>AE 2...

Temperature effects on Appearance energies of the ions P. Plessis et al., Can. J. Chem. 65 (1987) 1424, J. Phys. B, 16 (1983) 1770 H. M. Rosenstock, Int. J. Mass Spectr. Ion Phys., 20 (1976)139 Predicted by: Rosenstock – review article Plessis & Marmet – in CH 4 and C 2 H 6 papers

CH 4 e + CH 4 → CH e CH H + 2e CH H + 2e CH H - + 2e CH H - + 2e CH H 2 + 2e CH H 2 + 2e CH + + H 2 + H + 2e CH + + H 2 + H + 2e C + + 2H 2 + 2e C + + 2H 2 + 2e...

293K CH 4 + /CH 4 693K

ExperimentAE (eV) T=293 K AE (eV) T=693 K ΔAE (eV) Plessis et al. AE(eV) T=293 K CH 4 + /CH    0.02 CH 3 + /CH      0.08 E i (T) - rotational and vibrational energy of the molecule at T  E i =E i (693) – E i (293 K) ~ 0.12 eV Stano et al., J. Phys. B: At. Mol. Opt. Phys., 36 (2003) 261

CH 3 + /CH 4 693K 293K

CH 3 D + /CH 3 D AE 1 =12.75 eV AE 1 =12.62 eV 293K 693K

e+CH 3 D→AE(293K)AE(693K)D(AE(693K)- AE(293K)) (CH 3 D) ± ± ± 0.07 (CH 2 D) + + H – (CH 2 D) + + H ± ± ± ± ± ± 0.06

C 2 H 6 + /C 2 H 6 693K 293K

e + C 2 H 6 ExperimentTheory AE [eV] 293 K Thermochemistry [eV] G3B3 AIE [eV] C2H6+C2H ± C 2 H H - C 2 H H 12.06± ± ± C 2 H H ± ± C 2 H H + H ± ± C 2 H H ± ± C 2 H + +2H 2 +H C 2 H + +H 2 +3H25.7± ± ± C H ± ± C2H6C2H6C2H6C2H6

C 3 H 8 + /C 3 H 8 693K 293K

MoleculeΔAE (eV) Exp. ΔAE (eV) Theory CH CH 3 D CD C2H6C2H C3H8C3H Summary Temperatures 293 and 693 K

Isotopic effect on AE Changes in vibrational energies in isotopomers Heavy isotopomer – lower zero point energy => larger AE Comparison: CH 4, CD 4, CH 3 D

CH 3 D AE (eV) 293 K CD 4 AE (eV) 293 K CH 4 AE (eV) 293 K CH 3 D ± ± ± 0.04CH 4 + CH 2 D + + H – CH 2 D + + H ± ± ± ± ± 0.1 CH H – CH H Isotopic effect on AE

Present meV a) meV b) meV (CH 3 D) + /CH 3 D10050 (CH 2 D) + /CH 3 D80 (CH 3 ) + /CH 3 D200 (CHD) + /CH 3 D110 (CD 4 ) + /CD (CD 3 ) + /CD (CD 2 ) + /CD a) F. P. Lossing, A. W. Tickner, W. A. Bryce, J. Chem. Phys. 19, 1254 (1951). b) V. H. Dibeler, M. Krauss, R. M. Reese, F. N. Harlee J. Chem. Phys. 42, 3791 (1965). Isotopic shift

Conclusions experimentally observed dependence of AE´s on the temperature magnitude of the shift ~ vibrational and rotational excitation of the molecule confirmed isotopic shift in the appearance energies of the molecules

Contribution to new CRP Experiment: The temperature effects: -estimation of the partial cross sections in C 3 H 8 for particular fragment ions - evaluation of the rate coefficients Theory - QM: - Be n H m - electronic structure, binding energies, volatility, ionization potentials and electron affinities - H 2 reactions with Be n

Coworkers Comenius University Bratislava M. Stano, E. Vašeková, J.D. Skalný, D. Kubala, J. Kočíšek Theorists: I. Hubac, J. Urban, P. Mach S. Denifl, T.D. Märk University Innsbruck Support VW Stiftung, EU (Euroatom-FUSION), IAEA, APVT