Solvation suppression of ion recombination in gas discharge afterglow

An effect which suppresses recombination in ion plasmas is considered both theoretically and experimentally. Experimental results are presented for the ion recombination rate in fluorine plasma, which are obtained from data for the gas discharge afterglow. To interpret them, a suppression factor is considered: ion solvation in weakly ionized plasma. It is shown that the recombination process has a two-stage character with the formation of intermediate metastable ion pairs. The pairs consist of negative and positive ion-molecular clusters. A theoretical explanation is given for the slowing down of the ion recombination with the increase of the Coulomb coupling compared to the ion recombination rate calculated in the ideal plasma approximation. The approximate similarity of the recombination rate of the ion temperature and concentration and reasons for the slight deviation from the similarity are elucidated.

Figure 1

Dependence of the lifetime of the isolated metastable ion pair ${\mathrm{F}}^{-}{\left({\mathrm{F}}_2\right)}_{12}{{\mathrm{F}}_2}^{+}{\left({\mathrm{F}}_2\right)}_{12}$ on the inverse temperature. Open circles are the results of MD simulations and the solid line is Eq. (3).

Figure 2

Ratio of the ion recombination rate for the discharge afterglow plasma in fluorine to the ion recombination rate in the limit of the ideal plasmas. The data from Table 1 are shown by $◯$ for $P=100$ torr and $T$ = 500 K and $▽$ for $P$ = 60 torr and $T$ = 300 K. The model (17) is represented by a solid line for $T$ = 300 K and $P=60$ torr and by a dotted line for $T$ = 500 K and $P$ = 100 torr.

Figure 3

Ratio of the ion recombination rate for the discharge afterglow plasma in fluorine to the ion recombination rate in the limit of the ideal plasmas. The data from Table 1 are shown by $◯$ for $P=100$ torr and $T$ = 500 K and $▽$ for $P$ = 60 torr and $T$ = 300 K. The model (17) is represented by a solid line for $T$ = 300 K and $P=60$ torr and by a dotted line for $T$ = 500 K and $P$ = 100 torr. See the text for the break.