Utilizing different ratios of para to ortho H₂ in normal and para enriched hydrogen, we varied the population of para-H₃⁺ in an H₃⁺ dominated plasma at 77 K. Absorption spectroscopy was used to ...measure the densities of the two lowest rotational states of H₃⁺. Monitoring plasma decays at different populations of para-H₃⁺ allowed us to determine the rate coefficients for binary recombination of para-H₃⁺ and ortho-H₃⁺ ions: (p)α(bin)(77 K) = (1.9 ± 0.4) × 10⁻⁷ cm³ s⁻¹ and (o)α(bin)(77 K) = (0.2 ± 0.2) × 10⁻⁷ cm³ s⁻¹.
Using a low-temperature 22-pole ion trap apparatus, detailed measurements for the title reaction have been performed between 10 K and 100 K in order to get some state specific information about this ...fundamental hydrogen abstraction process. The relative population of the two lowest H{sub 2} rotational states, j = 0 and 1, has been varied systematically. NH{sup +} formation is nearly thermo-neutral; however, to date, the energetics are not known with the accuracy required for low-temperature astrochemistry. Additional complications arise from the fact that, so far, there is no reliable theoretical or experimental information on how the reactivity of the N{sup +} ion depends on its fine-structure (FS) state {sup 3} P{sub ja} . Since in the present trapping experiment, thermalization of the initially hot FS population competes with hydrogen abstraction, the evaluation of the decay of N{sup +} ions over long storage times and at various He and H{sub 2} gas densities provides information on these processes. First assuming strict adiabatic behavior, a set of state specific rate coefficients is derived from the measured thermal rate coefficients. In addition, by recording the disappearance of the N{sup +} ions over several orders of magnitude, information on nonadiabatic transitions is extracted including FS-changing collisions.
Using a low-temperature 22-pole ion trap apparatus, detailed measurements for the title reaction have been performed between 10 K and 100 K in order to get some state specific information about this ...fundamental hydrogen abstraction process. The relative population of the two lowest H sub(2) rotational states, j = 0 and 1, has been varied systematically. NH+ formation is nearly thermo-neutral; however, to date, the energetics are not known with the accuracy required for low-temperature astrochemistry. Additional complications arise from the fact that, so far, there is no reliable theoretical or experimental information on how the reactivity of the N+ ion depends on its fine-structure (FS) state super(3)Pja . Since in the present trapping experiment, thermalization of the initially hot FS population competes with hydrogen abstraction, the evaluation of the decay of N+ ions over long storage times and at various He and H sub(2) gas densities provides information on these processes. First assuming strict adiabatic behavior, a set of state specific rate coefficients is derived from the measured thermal rate coefficients. In addition, by recording the disappearance of the N+ ions over several orders of magnitude, information on nonadiabatic transitions is extracted including FS-changing collisions.
We present results of plasma afterglow experiments on ternary electron-ion recombination rate coefficients of H sub(3) super(+) and D sub(3) super(+) ions at temperatures from 50 to 300 K and compare ...them to possible three-body reaction mechanisms. Resonant electron capture into H sub(3)* Rydberg states is likely to be the first step in the ternary recombination, rather than third-body-assisted capture. Subsequent interactions of the Rydberg molecules with ambient neutral and charged particles provide the rate-limiting step that completes the recombination. A semiquantitative model is proposed that reconciles several previously discrepant experimental observations. A rigorous treatment of the problem will require additional theoretical work and experimental investigations.
Stabilization of H sub(3) super(+) collision complexes has been studied at nominal temperatures between 11 and 33 K using a 22-pole radio frequency (rf) ion trap. Apparent binary rate coefficients, k ...super(*) = k sub(r) + k sub(3)H sub(2), have been measured for para- and normal-hydrogen at number densities between some 10 super(11) and 10 super(14) cm super(-3). The state specific rate coefficients extracted for radiative stabilization, k sub(r)(T; j), are all below 2 10 super(-16) cm super(3) s super(-1). There is a slight tendency to decrease with increasing temperature. In contrast to simple expectations, k sub(r)(11 K; j) is for j = 0 a factor of 2 smaller than for j = 1. The ternary rate coefficients for p-H sub(2) show a rather steep T-dependence; however, they are increasing with temperature. The state specific ternary rate coefficients, k sub(3)(T; j), measured for j = 0 and derived for j = 1 from measurements with n-H sub(2), differ by an order of magnitude. Most of these surprising observations are in disagreement with predictions from standard association models, which are based on statistical assumptions and the separation of complex formation and competition between stabilization and decay. Most probably, the unexpected collision dynamics are due to the fact that, at the low translational energies of the present experiment, only a small number of partial waves participate. This should make exact quantum mechanical calculations of k sub(r) feasible. More complex is three-body stabilization, because it occurs on the H sub(5) super(+) potential energy surface.
Recombination of HCO
+ and DCO
+ ions with electrons was studied in afterglow plasma. The flowing afterglow with Langmuir probe (FALP) apparatus was used to measure the recombination rate ...coefficients and their temperature dependencies in the range 150–270
K. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The variations of
α
HC
O
+
(
T
)
and
α
DC
O
+
(
T
)
seem to obey the power law:
α
HC
O
+
(
T
)
=
(2.0
±
0.6)
×
10
−7
(
T/300)
−1.3
cm
3
s
−1 and
α
DC
O
+
(
T
)
=
(1.7
±
0.5)
×
10
−7
(
T/300)
−1.1
cm
3
s
−1 over the studied temperature range.
The kinetics of the reactions of the ion SH+ with CH4 and C2H2 and SiH+ with C2H2 and NH3 has been investigated using selected ion flow drift tube technique (SIFDT). The reaction rate coefficients ...and the products branching ratio have been determined as a functions of the reactant ion/reactant neutral average centre-of-mass kinetic energy (KECM=0.05–2eV). The studied reactions are fast at thermal and near thermal energies and have negative energy dependencies of the reaction rate coefficients.
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