Abstract

Measurements in H(3)(+) afterglow plasmas with spectroscopically determined relative abundances of H(3)(+) ions in the para-nuclear and ortho-nuclear spin states provide clear evidence that at low temperatures (77-200 K) para-H(3)(+) ions recombine significantly faster with electrons than ions in the ortho state, in agreement with a recent theoretical prediction. The cavity ring-down absorption spectroscopy used here provides an in situ determination of the para/ortho abundance ratio and yields additional information on the translational and rotational temperatures of the recombining ions. The results show that H(3)(+) recombination with electrons occurs by both binary recombination and third-body (helium) assisted recombination, and that both the two-body and three-body rate coefficients depend on the nuclear spin states. Electron-stabilized (collisional-radiative) recombination appears to make only a small contribution.

The electron-temperature dependence of the recombination of H3O+(H2O)n cluster-ions with electrons has been measured in an afterglow experiment in which the electrons were heated by a radio-frequency electric field. The recombination coefficients were found to vary with electron temperature Te as ∼Te−1/2, in better agreement with theoretical expectations than earlier results of microwave-afterglow measurements.

No abstract

Several ion–molecule reactions of ionospheric interest have been studied in a drift-tube–mass-spectrometer apparatus for ions of mean energy from thermal energies to ∼ 1 eV. The measured rate coefficients in cubic centimeters/second are N++O2: 5 × 10−10 from 0.039–0.9 eV; N2++O2: 6 × 10−11 at 0.039 eV, decreasing to ∼ 8 × 10−12 at 0.9 eV; O2++NO: 3 × 10−10 from 0.039–1.6 eV; O++CO2: 1 × 10−9 at 0.039 eV, decreasing to 5 × 10−10 cm3/sec at 1.3 eV. The relevance of the first three reactions for the Earth's ionosphere and of the last reaction for the Martian atmosphere is discussed briefly.

No abstract

No abstract

No abstract