_{3}: Experiments and kinetic modeling

^{1}, Thomas M. Miller

^{1}, Jeffrey F. Friedman

^{1}, Albert A. Viggiano

^{1}, Anatol I. Maergoiz

^{2}and Jürgen Troe

^{2,3,a)}

### Abstract

The kinetics of electron attachment to CF_{3} as a function of temperature (300–600 K) and pressure (0.75–2.5 Torr) were studied by variable electron and neutral density attachment mass spectrometry exploiting dissociative electron attachment to CF_{3}Br as a radical source. Attachment occurs through competing dissociative (CF_{3} + e^{−} → CF_{2} + F^{−}) and non-dissociative channels (CF_{3} + e^{−} → CF_{3} ^{−}). The rate constant of the dissociative channel increases strongly with temperature, while that of the non-dissociative channel decreases. The rate constant of the non-dissociative channel increases strongly with pressure, while that of the dissociative channel shows little dependence. The total rate constant of electron attachment increases with temperature and with pressure. The system is analyzed by kinetic modeling in terms of statistical theory in order to understand its properties and to extrapolate to conditions beyond those accessible in the experiment.

The project was funded by the United States Air Force of Scientific Research under Project No. 2303EP. Financial support by the European Office of Aerospace Research and Development (Grant No. FA8655-10-1-3057) is also acknowledged. T.M.M. is under contract (No. FA8718-10-C-0002) from the Institute for Scientific Research of Boston Colleagues. A.I.M. gratefully acknowledges support by the Deutsche Forschungsgemeinschaft (TR 69/17-2).

I. INTRODUCTION

II. EXPERIMENTAL METHOD AND RESULTS

III. KINETIC MODELING OF THE EXPERIMENTAL RESULTS

IV. PREDICTIONS FROM KINETIC MODELING

V. CONCLUSIONS

### Key Topics

- Reaction rate constants
- 32.0
- Dissociation
- 19.0
- Electroluminescence
- 13.0
- Plasma flows
- 10.0
- Plasma etching
- 8.0

## Figures

Relative anion abundances 4.6 ms after the addition of 2.6 × 10^{−9} cm^{−3} CF_{3}Br to the afterglow as a function of the initial electron density at 400 K and 1.33 Torr. Solid lines are best-fit calculated abundances (see text); dashed lines (shown only for F^{−}) are calculated abundances at the uncertainty limits of *k* _{F}-.

Relative anion abundances 4.6 ms after the addition of 2.6 × 10^{−9} cm^{−3} CF_{3}Br to the afterglow as a function of the initial electron density at 400 K and 1.33 Torr. Solid lines are best-fit calculated abundances (see text); dashed lines (shown only for F^{−}) are calculated abundances at the uncertainty limits of *k* _{F}-.

Projections of the weighted least-squares goodness-of-fit of calculated to experimental anion abundances (see text), for the data shown in Fig. 1, on to three parameters (*k* _{tot}, , ) for which results are reported in this work.

Projections of the weighted least-squares goodness-of-fit of calculated to experimental anion abundances (see text), for the data shown in Fig. 1, on to three parameters (*k* _{tot}, , ) for which results are reported in this work.

Rate constants for total electron attachment to CF_{3}, *k* _{ tot,} (full circles) and the competing dissociative, , (open circles) and non-dissociative, , (open squares) product channels at *T* = 300 K. Some data points are slightly offset horizontally for clarity. Experimental data (symbols) and kinetic modeling (lines) are compared with modeled *k* _{ at }, corresponding to primary attachment.

Rate constants for total electron attachment to CF_{3}, *k* _{ tot,} (full circles) and the competing dissociative, , (open circles) and non-dissociative, , (open squares) product channels at *T* = 300 K. Some data points are slightly offset horizontally for clarity. Experimental data (symbols) and kinetic modeling (lines) are compared with modeled *k* _{ at }, corresponding to primary attachment.

Rate constants for total electron attachment to CF_{3}, *k* _{ tot } = + (full circles), and the competing dissociative (open circles), and non-dissociative, (open squares), product channels at *T* = 300 K. Some data points are slightly offset horizontally for clarity. Experimental data (symbols) and kinetic modeling (lines) are compared with modeled *k* _{ at }, corresponding to primary attachment.

Rate constants for total electron attachment to CF_{3}, *k* _{ tot } = + (full circles), and the competing dissociative (open circles), and non-dissociative, (open squares), product channels at *T* = 300 K. Some data points are slightly offset horizontally for clarity. Experimental data (symbols) and kinetic modeling (lines) are compared with modeled *k* _{ at }, corresponding to primary attachment.

As Fig. 4, but for *T* = 600 K.

As Fig. 4, but for *T* = 600 K.

Modeled specific rate constants *k* _{ det }(*E*) for electron detachment from CF_{3} ^{−*} (barrier-determining modes *ν* = 503 cm^{−1}: left curve; 691 cm^{−1}: middle curve; 1224 cm^{−1}: right curve; see text).

Modeled specific rate constants *k* _{ det }(*E*) for electron detachment from CF_{3} ^{−*} (barrier-determining modes *ν* = 503 cm^{−1}: left curve; 691 cm^{−1}: middle curve; 1224 cm^{−1}: right curve; see text).

Modeled specific rate constants *k* _{ dis }(*E*) for dissociation of CF_{3} ^{−*} to F^{−} + CF_{2} (looseness parameter *c* _{ loose } = 100 cm^{−1}: lower curve; *c* _{ loose } = 1000 cm^{−1}: middle curve; *c* _{ loose } = ∞(PST): upper curve; see text).

Modeled specific rate constants *k* _{ dis }(*E*) for dissociation of CF_{3} ^{−*} to F^{−} + CF_{2} (looseness parameter *c* _{ loose } = 100 cm^{−1}: lower curve; *c* _{ loose } = 1000 cm^{−1}: middle curve; *c* _{ loose } = ∞(PST): upper curve; see text).

Modeled distribution functions *g(E,T)* of the internal energy *E* of CF_{3} ^{−*} generated by thermal electron attachment to CF_{3} (full lines) in comparison to thermal energy distributions of CF_{3} (dashed lines) (with *P* ^{IVR} from Eq. (15) and the other parameters corresponding to the fit to the experiments shown in Figs. 3–5, see text, full lines shifted upward for clarity).

Modeled distribution functions *g(E,T)* of the internal energy *E* of CF_{3} ^{−*} generated by thermal electron attachment to CF_{3} (full lines) in comparison to thermal energy distributions of CF_{3} (dashed lines) (with *P* ^{IVR} from Eq. (15) and the other parameters corresponding to the fit to the experiments shown in Figs. 3–5, see text, full lines shifted upward for clarity).

Modeled primary attachment rate constants *k* _{ at } for *T* _{ gas } = T_{el} (P^{IVR} from Eq. (13) with = 67 cm^{−1}: full line; *P* ^{IVR} from Eq. (15) with = 33 cm^{−1}; dashed line; the other parameters correspond to the fit to the experiments shown in Figs. 3–5).

Modeled primary attachment rate constants *k* _{ at } for *T* _{ gas } = T_{el} (P^{IVR} from Eq. (13) with = 67 cm^{−1}: full line; *P* ^{IVR} from Eq. (15) with = 33 cm^{−1}; dashed line; the other parameters correspond to the fit to the experiments shown in Figs. 3–5).

As Fig. 9, but with fixed gas temperature *T* _{ gas } = 300 K and variable electron temperature *T* _{ el }.

As Fig. 9, but with fixed gas temperature *T* _{ gas } = 300 K and variable electron temperature *T* _{ el }.

Modeled branching fractions (dashed lines), (dotted lines), and *Y* _{ tot } = + (full lines) as a function of the bath gas (He) pressure and the temperature *T* = *T* _{ gas } = *T* _{ el }.

Modeled branching fractions (dashed lines), (dotted lines), and *Y* _{ tot } = + (full lines) as a function of the bath gas (He) pressure and the temperature *T* = *T* _{ gas } = *T* _{ el }.

## Tables

Measured rate constants (with high and low uncertainty limits in parentheses) along with modeled rate constants (values behind the slash).

Measured rate constants (with high and low uncertainty limits in parentheses) along with modeled rate constants (values behind the slash).

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