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1 PROBING THE GAS PHASE CHEMISTRY INVOLVED IN DIAMOND CHEMICAL VAPOUR DEPOSITION (CVD) Mike Ashfold School of Chemistry University of Bristol Bristol BS8.

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Presentation on theme: "1 PROBING THE GAS PHASE CHEMISTRY INVOLVED IN DIAMOND CHEMICAL VAPOUR DEPOSITION (CVD) Mike Ashfold School of Chemistry University of Bristol Bristol BS8."— Presentation transcript:

1 1 PROBING THE GAS PHASE CHEMISTRY INVOLVED IN DIAMOND CHEMICAL VAPOUR DEPOSITION (CVD) Mike Ashfold School of Chemistry University of Bristol Bristol BS8 1TS

2 2 Chemical vapour deposition of diamond films Activation of gas mixture by Hot filament (T fil ~2450 K) Microwave plasma DC arc jet Polycrystalline films grow on Si, Mo, W, … substrates; T sub > 700 ° C. Growth of single crystal diamond by CVD demonstrated (Isberg et al, Science, 297, 1670 (2002)) Properties: High thermal conductivity Optical transparency (UV mid IR) Chemically inert Electrical insulator – can be doped

3 3 SEM images of polycrystalline CVD diamond

4 4 Film characterisation by Raman spectroscopy Raman Shift / cm Intensity / arb. units 1332 cm -1

5 5 Recent studies by the Bristol Diamond Group Hydrocarbon / H 2 mixtures in a hot filament (HF) reactor Molecular beam mass spectrometry Laser probing H atoms, CH 3 radicals and C 2 H 2 molecules Modelling CH 4 / H 2 and C 2 H 2 / H 2 gas mixtures (Ashfold et al., Phys. Chem. Chem. Phys. (2001), 3, 3471) Probing and modelling CH 4 /NH 3 /H 2 gas mixtures (Smith et al., J. Appl. Phys. (2002), 92, 672) CO 2 / CH 4 mixtures in a microwave (MW) reactor Molecular beam mass spectrometry Modelling H/C/O gas phase chemistry Effect of S additions (as H 2 S or CS 2 ) (Petherbridge et al., J. Appl. Phys. (2001), 89, 1484, 5219) CH 4 / H 2 / Ar mixtures in a DC arc jet reactor Cavity ring down measurements of C 2 H 2 and of C 2 and CH radicals Modelling plasma activated CH 4 / H 2 gas mixtures (Wills et al., J. Appl. Phys. (2002), 92, 4213 Rennick et al., Chem. Phys. Lett. (2004), 383, 518 Rennick et al., Diam. Rel. Mater. (2004), 14, 561)

6 6 Diamond film growth in a hot filament reactor 0.5-1% CH 4 in H 2 Total flow rate = 100 sccm Pressure = 20 Torr Film growth rate ~ 1 m/hr

7 7 In situ molecular beam mass spectrometry, I 1%CH 4 / H 2 Gas mixture sampled through a skimmer by a differentially pumped quadrupole mass spectrometer, equipped with variable energy electron ioniser. X [CH 4 ] ~ X [C 2 H 2 ]

8 8 Predictions from equilibrium thermodynamics [CH 4 ] ~ [C 2 H 2 ] at T gas ~ 1500 K Gas temperature / K

9 9 In situ molecular beam mass spectrometry, II 0.5%C 2 H 2 /H 2 Equilibrium thermodynamics predicts no C 2 H 2 CH 4 conversion! X [CH 4 ] ~ X [C 2 H 2 ]

10 10 MBMS probing HF-CVD reactors: Conclusions Near HF (i.e. where T gas > 1400 K) the hydrocarbon is present as a CH 4 C 2 H 2 mixture, irrespective of original source gas used. High [hydrocarbon] increased growth rates, but poorer diamond quality (as assessed by morphology, Raman etc.) High [H] reduced growth rates, but improved diamond quality. Large T gradients near HF preferential diffusion of heavier species (i.e. hydrocarbons) from hotter regions - Soret effect. CH 3 is a key diamond growth species in weakly activated hydrocarbon / H 2 gas mixtures. Narrow range of T fil for optimal diamond growth: - Low T fil : insufficient H 2 H dissociation, - High T fil : CH 4 C 2 H 2 equilibrium shifts far to right, and [CH 3 ] in the growth region falls.

11 11 Ideal requirements of a diagnostic Species selectivity High sensitivity Spatial (and temporal) resolution Minimal intrusion Ease of implementation Readily interpretable results laser spectroscopy Resonance enhanced multiphoton ionisation (REMPI) for H atoms and CH 3 radicals in HF-CVD reactor – spatially resolved (relative) number densities. Cavity ring down spectroscopy (CRDS) for CH(X), C 2 (a) and C 2 (X) radicals, and C 2 H 2 molecules, in DC-arc jet reactor – spatially resolved (absolute) column densities

12 12 Hydrogen atoms, I H atoms are crucial in most diamond CVD environments. They: Initiate gas phase chemistry ( reactive C containing species) Terminate the growing diamond surface, preventing reconstruction Abstract surface H to create vacant sites for C-radical attachment Etch non-diamond deposits such as graphite. n = 1 n = 2 n = 3 ionisation continuum Probe by 2+1 REMPI in HF activated hydrocarbon / H 2 gas mixtures Move filament and substrate relative to laser beam focus to obtain spatially resolved number density distributions Collect H + ions with a biased Pt probe

13 13 Hydrogen atoms, II Measure H + ion yield as a function of laser excitation wavenumber. Laser bandwidth makes negligible contribution to measured 2s 1s lineshape. Area of lineshape local number density of H atoms, N H. Local gas temperature obtained from FWHM of Doppler broadened (Gaussian) lineshape.

14 14 Hydrogen atoms, III T gas vs d, fixed T fil. T gas (from FWHM values) declines monotonically with distance, d, from the HF. N H vs d, fixed T fil. N H falls with increasing d, but much more slowly than would be predicted by assuming that the H 2 2H equilibrium was determined by the local T gas.

15 15 Hydrogen atoms, IV Measured N H dependences are consistent with H atom formation by dissociative chemisorption of H 2 on HF surface, and subsequent diffusion throughout reactor. Gas phase H atom recombination is very inefficient when H 2 is the main third body. N H independent of p(H 2 ) – zero order kinetics N H increases rapidly with T fil

16 16 Methyl radicals, I CH 3 radicals can be detected by 2+1 REMPI via the v = 0 level of the 3p z, 2 A 2 Rydberg state. The two photon transition from the ground state is dominated by an intense Q branch. To convert measured REMPI intensities into CH 3 radical number densities we must correct for the T gas dependence of: (i) the vibrational partition function (ii) the rotational band contour Simulation Experimental Two-photon wavenumber / cm -1

17 17 Methyl radicals, II [CH 3 ] vs d from HF activated CH 4 /H 2 and C 2 H 2 /H 2 mixtures 1% CH 4 / H 2 0.5% C 2 H 2 / H 2 Corrected Raw Data

18 18 Methyl radicals, III [CH 3 ] vs %C and vs T fil for 1% CH 4 /H 2 ( ) and 0.5% C 2 H 2 /H 2 (o), probed at d = 4 mm, plotted to match at 0.5% C and at T fil = 2575 K. All measured [CH 3 ] dependences are explicable in terms of gas phase chemistry.

19 19 Gas phase reaction mechanism - qualitative CH 4 /H 2 chemistry: Radical formation: H + CH 4 CH 3 + H 2 (H-shifting reactions)H + CH 3 CH 2 + H 2, etc. C 1 C 2 conversion: CH 3 + CH 3 + M C 2 H 6 + M C 2 H 6 + H C 2 H 5 + H 2 …… C 2 H 2 + H 2 C 2 H 2 /H 2 chemistry: Analogous H + C 2 H 2 C 2 H + H 2 radical initiation step is endothermic. Earlier models often invoked a role for heterogeneous chemistry (on surface of HF, or on the growing diamond film), but spatially resolved [CH 3 ] profiles led us to suggest that gas phase addition processes like C 2 H 2 + H + M C 2 H 3 + M may occur in cooler regions of the reactor.

20 20 Gas phase reaction mechanism - quantitative 3-D modelling of the Bristol HF-CVD reactor. (Mankelevich and Suetin, Moscow State University) Model consists of 3 blocks that describe: activation (gas heating, H 2 dissociation on filament) gas phase processes (heat and mass transfer, reaction kinetics) gas-surface processes at the substrate Gas phase reaction kinetics and thermochemistry from GRIMECH 3.0 detailed reaction mechanism for C/H/(O/N) mixtures. Conservation equations for mass, momentum, energy and number densities are integrated numerically until steady-state is achieved. Model outputs include spatial distributions of gas temperature, flow field and species number densities.

21 21 Summary of elementary reaction rates Reaction Rate / cm -3 s -1 Reaction 730 K 1200 K 1750 K 2000 K H + C 2 H 2 + M C 2 H 3 + M 1.85E E E E +14 C 2 H 3 + M H + C 2 H 2 + M 3.72E E E E +16 H + C 2 H 3 H 2 + C 2 H E E E E +15 H 2 + C 2 H 2 H + C 2 H E E E E +13 Total: C 2 H 2 C 2 H E E E E +16 Total: C 2 H 3 C 2 H E E E E +16 Total: C 2 H 4 C 2 H E E E E +15 Total: C 2 H 6 /C 2 H 5 CH E E E E +15 Total: C 2 H 6 C 2 H E E E E +15 Entries in red confirm the suggestion that, at low T gas, there is net C 2 C 1 conversion via C 2 H 2 C 2 H 3 C 2 H 4 C 2 H 5 CH 3.

22 22 CH 4 C 2 H 2 interconversion lower T gas ; net C 2 H 2 CH 4 high T gas ; net CH 4 C 2 H 2

23 23 Experiment and theory compared 1% CH 4 / H 2 0.5% C 2 H 2 / H 2 T fil = 2475 K modelexpt.

24 24 Conclusions from studies of HF-activated CH 4 /H 2 and C 2 H 2 /H 2 gas mixtures With CH 4 /H 2 input mixtures, gas phase H abstraction reactions initiate the overall CH 4 C 2 H 2 conversion in regions of high T gas near the HF. Diffusion rates are much faster than gas replacement rates in these reactors (typical gas flow rate ~100 sccm), so much of the C 2 H 2 formed by CH 4 C 2 H 2 conversion near the HF will diffuse to cooler regions. (confirmed by cw CRDS monitoring of C 2 H 2 rotational temperature and the time constants for its build up and decay – Wills et al., Diamond Rel. Mater. (2003), 12, 1346) H addition reactions in cooler regions of the reactor drive the reverse C 2 H 2 CH 4 conversion, offering a means of regenerating methane and eventual CH 4 C 2 H 2 equilibration. Purely gas phase processes can account for the observed C 2 C 1 interconversion in CH 4 /H 2 and C 2 H 2 /H 2 input gas mixtures.

25 25 Recent gas phase diagnostics studies in Bristol Hydrocarbon / H 2 mixtures in a hot filament (HF) reactor Molecular beam mass spectrometry of stable species REMPI laser probing H atoms and CH 3 radicals Modelling CH 4 / H 2 and C 2 H 2 / H 2 gas mixtures (Ashfold et al., Phys. Chem. Chem. Phys. (2001), 3, 3471) Probing and modelling CH 4 /NH 3 /H 2 gas mixtures (Smith et al., J. Appl. Phys. (2002), 92, 672) CO 2 / CH 4 mixtures in a microwave (MW) reactor Molecular beam mass spectrometry Modelling H/C/O gas phase chemistry CH 4 / H 2 / Ar mixtures in a DC arc jet reactor Cavity ring down measurements of C 2 H 2 and of C 2 and CH radicals Modelling plasma activated CH 4 / H 2 gas mixtures (Wills et al., J. Appl. Phys. (2002), 92, 4213 Rennick et al., Chem. Phys. Lett. (2004), 383, 518 Rennick et al., Diam. Rel. Mater. (2004), 14, 561)

26 26 Diamond film growth in a DC arc jet How to probe gas phase chemistry and composition? Optical emission spectroscopy (OES) and cavity ring down spectroscopy (CRDS). 10 kW DC arc jet 1%CH 4 in Ar/H 2 at 50 Torr Growth rates ~100 m hr -1 Aggressive activation: much higher gas temperatures and flow rates than in HF or MW reactors.

27 27 DC arc jet in operation diamond film growing on Mo substrate plasma jet CH 4 injection ring

28 28 Diamond films grown with DC arc jet SEM images of polycrystalline diamond films grown in the DC arc jet

29 29 Optical emission from the arc jet plume What are primary growth species in this highly activated environment? C atoms? C 2 radicals? Latter show strongly in optical emission. C 2 Swan system (d 3 g a 3 u ) Spatially resolved C 2 (d-a) emission

30 30 Proposed mechanism for diamond growth by C 2 C 2 addition to H-terminated and to bare diamond (110) surfaces has been calculated to be barrierless and exothermic. (D.A. Horner et al. Chem. Phys. Lett. 233 (1995) 243)

31 31 In situ diagnosis of the arc jet plume, I Optical emission spectroscopy (OES) Only fluorescent species can be observed. Provides information about the (minor) electronically excited components in plume – how to relate to ground state concentrations, properties, etc? Spatially resolved measurements difficult. Resonance enhanced multiphoton ionisation (REMPI) Used successfully to probe ground state H atoms and CH 3 radicals in HF reactor, but ion probe will not survive harsh plasma environment and background ion/electron signal would be a problem. Laser induced fluorescence (LIF) Species of interest must have fluorescent excited state. Need to quantify excited state quenching characteristics in order to relate measured LIF signal intensities to ground state populations of interest. Detector likely to be overwhelmed by intense spontaneous emission from plume.

32 32 In situ diagnosis of the arc jet plume, II Absorption spectroscopy Beer-Lambert behaviour I = I 0 exp{- [X] L} Advantages: Straightforward General Quantitative Disadvantages: Insensitive Non-selective Fractional absorption per pass I = (I 0 – I)/I

33 33 In situ diagnosis of the arc jet plume, III Intra-cavity absorption spectroscopy Build cavity around sample Multipass a light pulse Detect rate of loss of light Cavity ring-down spectroscopy I(t) = I 0 exp{-k 0 t - ct} ; = [X] ; I min ~ Change in ring-down rate as a function of excitation wavelength gives the absorption spectrum

34 34 Cavity Ring Down Spectroscopy in the DC arc jet Variables include: - CH 4 flow rate - power into plasma - distance from substrate

35 35 C 2 (a) radical detection Portion of C 2 d 3 g a 3 u (0,0) band integrated absorption coefficient of measured line A 00 = Einstein A coefficient for vibronic transition of interest. p = fraction of total oscillator strength within probed rovibrational transition (T dependent). C 2 (a, v = 0) column density. C 2 (a) number density IF we know T gas (and thus q vib ) and the absorbing column length, L (from OES). [C 2 (a 3 u )] ~ cm -3 for 3.3%CH 4 /H 2 gas mixture, 6 kW input power, assuming T gas = 3300 K and L = 1 cm. (

36 36 C 2 (a) radical detection – gas temperature determination Boltzmann plots of C 2 (a) rotational state population distribution measured in the plume (2 < z < 25 mm) give T rot = K. Doppler linewidth analyses give similar T gas for z > 5mm, but overestimate T gas close to the substrate – a consequence of plume flaring in the boundary layer. probe

37 37 C 2 (X) radical detection T vib = K [C 2 (X 1 g )] = ( ) cm -3 again assuming L = 1 cm. = c.f if the a and X states of C 2 were in thermal equilibrium at 3300 K – implies intersystem crossing is faster than reaction (with e.g. H 2 ) under operational conditions. Portion of C 2 (D 1 u X 1 g ) spectrum recorded in free plume at ~ 235 nm

38 38 CH(X) radical detection Portion of CH A 2 X 2 (0,0) band ~ 427 nm Non-zero absorbance between peaks probably attributable to C 3 radicals. [CH(X )] = ( ) cm -3 in the free plume under normal operating conditions. (again assuming L = 1 cm).

39 39 C 2 (a) and CH(X) radical column densities as fn(z) 3% CH 4 /H 2, 6 kW input power, range of probe transitions C 2 (a)CH(X)

40 40 C 2 (a) and CH(X) radical column densities as fn[CH 4 ] x sccm CH 4 / 1.8 slm H 2 / 12.2 slm Ar Arc jet power 6 kW, range of probe transitions C 2 (a)CH(X)

41 41 cw CRDS probing of C 2 H 2 in the DC arc jet reactor ECDL: Littman configuration extended cavity diode laser AOM: acousto-optic modulator

42 42 cw CRDS probing of C 2 H 2 in the DC arc jet reactor R(22) line of combination band of C 2 H 2 = cm -1 ( MHz). pressure broadening: ~200 MHz at 50 Torr laser bandwidth: ~4 MHz T gas = K C 2 H 2 present along whole viewing column? [C 2 H 2 ] = cm -3 for 0.83% CH 4 /H 2 feed (i.e. only 25% of our standard CH 4 flow rate) and assuming L = 100 cm

43 43 CRDS in DC arc jet: summary of experimental findings Probing in the free plume region of the arc jet, with a CH 4 flow of 60 sccm: [C 2 (a)] ~ 1.1 x cm -3, [C 2 (X)] ~ 3 x cm -3, [CH(X)] ~ 7 x cm -3 (all assuming L = 1 cm ) T gas = K [C 2 H 2 ] ~ 1.2 x cm -3 (using a reduced (15 sccm) CH 4 flow, assuming L =100 cm) T gas ~ 550 K There is a boundary region close to the substrate, where C 2 and CH column densities increase – due to plume flaring and the longer L? Increased linewidths at small z mainly due to plume flaring. Internal quantum state population distributions of radical species suggest T gas relatively insensitive to z. [C 2 H 2 ], and T gas value (average over all L?) is insensitive to z in range 2 – 25 mm.

44 44 Modelling of the DC arc jet plume (Mankelevich) 2-D (r,z) model, comprising of three blocks, describing: (i) activation of the reactive mixture (i.e. gas heating, ionisation, H 2 dissociation in arc jet and intermediate chamber, H atom loss and H 2 production on nozzle exit walls), (ii) gas-phase processes (heat and mass transfer, chemical kinetics), (iii) gas-surface processes at the substrate. Thermochemical data and the reduced chemical reaction mechanism builds on Yu.A. Mankelevich et al., Diam. Rel. Mater. (1996), 5, 888. Chemical kinetics scheme involves 23 species (H, H 2, Ar, C, CH, 3 CH 2, 1 CH 2, CH 3, CH 4, C 2 (X), C 2 (a), C 2 H x (x = 1-6), C 3 H x (x = 0-2), C 4 H x (x = 0-2)) and 76 reversible reactions. Set of conservation equations for mass, momentum, energy and species concentrations, with appropriate initial and boundary conditions, thermal and caloric equations of state, are integrated numerically in cylindrical (r,z) coordinate space until attaining steady state conditions. Model output includes spatial distributions of T gas, the flow field, and the various species number densities.

45 45 Modelling of the DC arc jet plume: T gas Gas temperature distribution, T gas substrate methane injection ring H 2 /Ar plasma enters here

46 46 Modelling of the DC arc jet plume: H T gas H: H 2 >90% dissociated; high [H] at substrate.

47 47 Modelling of the DC arc jet plume: CH 4 T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring

48 48 Modelling of the DC arc jet plume: C 2 H 2 T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2

49 49 Modelling of the DC arc jet plume: C 4 H 2 T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 )

50 50 Modelling of the DC arc jet plume: C 3 T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 ) and C 3 radicals

51 51 Modelling of the DC arc jet plume: C 2 H T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 ) and C 3 radicals larger C x H y species break down as [H] and T gas increase in the vicinity of the plume C 2 H

52 52 Modelling of the DC arc jet plume: C 2 T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 ) and C 3 radicals larger C x H y species break down as [H] and T gas increase in the vicinity of the plume C 2 H, C 2,

53 53 Modelling of the DC arc jet plume: CH T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 ) and C 3 radicals larger C x H y species break down as [H] and T gas increase in the vicinity of the plume C 2 H, C 2, CH radicals

54 54 Modelling of the DC arc jet plume: C T gas H: H 2 >90% dissociated; high [H] at substrate. CH 4 injected through ring rapidly converted to C 2 H 2 and to larger C x H y compounds (e.g. C 4 H 2 ) and C 3 radicals larger C x H y species break down as [H] and T gas increase in the vicinity of the plume C 2 H, C 2, CH radicals and C atoms C 1 H y formation on axis requires high [H] and T gas, and sufficient time for diffusion into core of plume

55 55 Summary of results from modelling arc jet plume Gas temperature and flow velocity distributions show a cylindrical hot plume with T gas ~ K, in good accord with optical emission studies. Highly activated gas mixture. [H]/[H 2 ] ratio just above the substrate is ~ 0.25 (cf ~0.01 in typical low power HF or MW PECVD reactors). Surface chemistry is dominated by H abstraction and addition reactions. Gas pressure is not uniform throughout the chamber - encouraging the recirculation needed to transfer hydrocarbon from injection ring into the hot plume. Numerous chemical transformations occur during this transport. Predicted number densities of C, CH, C 2, C 2 H, C 2 H 2 and C 3 incident on the growing diamond surface are all >10 12 cm -3. Most, if not all, of these species must contribute to film growth given the high (~3%) utility of carbon source gas deduced experimentally by comparing observed film growth rates with the metered CH 4 input.

56 56 Comparison with experiment: CH and C 2 (a) Model confirms that CH and C 2 species are localised in the hot plume. Quantitative agreement between observed and modelled column densities and rotational temperatures (~3300 K). Larger Doppler width seen at small z due to flaring of plume along observation axis. C 2 H 2 predicted to be present throughout reactor – consistent with observed number densities and low (~550 K) associated average temperature.

57 57 Present and Future Work CRDS monitoring of CH(X) radicals in HF activated CH 4 /H 2 and C 2 H 2 /H 2 gas mixtures, and comparison with model predictions Probing B atoms in HF activated B 2 H 6 /CH 4 /H 2 gas mixtures (by 2+1 REMPI at ~346 nm and by CRDS at ~249 nm) with a view to unravelling gas phase chemistry involved in B doped CVD diamond growth. Ab initio calculation of relevant elementary B/C/H gas phase and gas-surface reactions (with Harvey, Bristol), and modelling of full gas phase reaction mechanism (with Mankelevich). Spatially resolved CRDS measurements in arc-jet reactor to explore radial profiles of radical species in the plume. Extension of CRDS studies to new high pressure microwave activated CVD reactor designed for optical diagnosis.

58 58 Acknowledgements Andrew Orr-Ewing Paul May Colin Western Keith Rosser James Smith Steve Redman Roland Tsang James Petherbridge Mark Wallace Jon Wills Andrew Cheesman Chris Rennick William Boxford Alistair Smith Dane Comerford Yuri Mankelevich Nikolay Suetin (Moscow State Univ.)

59 59 Reaction Rate / cm -3 s -1 Reaction730 K1200 K1750 K2000 K H + C 2 H 2 + M C 2 H 3 + M1.85E E E E +14 C 2 H 3 + M H + C 2 H 2 + M3.72E E E E +16 H + C 2 H 3 H 2 + C 2 H E E E E +15 H 2 + C 2 H 2 H + C 2 H E E E E +13 Total: C 2 H 2 C 2 H E E E E+16 H + C 2 H 4 H 2 + C 2 H E E E E +16 C 2 H 3 + H 2 H + C 2 H E E E E +16 H + C 2 H 3 + M C 2 H 4 + M3.12E E E E +12 C 2 H 4 + M H + C 2 H 3 + M05.25E E E +13 Total: C 2 H 3 C 2 H E E E E+16 C 2 H 4 + M H 2 + C 2 H 2 + M4.14E E E E +15 H + C 2 H 4 + M C 2 H 5 + M5.02E E E E +13 C 2 H 5 + M H + C 2 H 4 + M3.15E E E E +15 H + C 2 H 5 H 2 + C 2 H E E E E +13 H 2 + C 2 H 4 H + C 2 H E E E +11 Total: C 2 H 4 C 2 H E E E E+15 CH 3 + CH 3 + M C 2 H 6 + M4.22E E E E +13 C 2 H 6 + M CH 3 + CH 3 + M6.74E E E E +15 CH 3 + CH 3 H + C 2 H E E E E +14 H + C 2 H 5 CH 3 + CH E E E E +15 Total: C 2 H 6 /C 2 H 5 CH E E E E+15 H + C 2 H 6 H 2 + C 2 H E E E E +15 C 2 H 5 + H 2 H + C 2 H E E E E +14 H + C 2 H 5 + M C 2 H 6 + M1.63E E E E +11 C 2 H 6 + M H + C 2 H 5 + M02.10E E E +13 Total: C 2 H 6 C 2 H E E E E+15

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