Luminescence measurements of Xe(+) + N2 and Xe(2+) + N2 hyperthermal charge transfer collisions

Luminescence Measurements of the Hyperthermal Reactions of N/N+ + NH3

Chemiluminescence from a system of collisions, N⁺/N/Kr⁺/Kr/Xe⁺/Xe + NH₃, at collision energies between 10 and 170 eV (center of mass, COM), was measured in the spectral range 300-1000 nm. The energy dependence of the emission excitation cross sections was quantified, and molecular signatures were fit to known spectroscopic constants to determine vibrational-state populations. For both N and N⁺ collision species, the strongest features were assigned to emissions from NH (A-X) and the atomic hydrogen Balmer series. For each of the spectra resulting from collisions with primary cations, the NH (A-X) emissions had the largest cross sections reaching values of (1.0-1.5) × 10^-18 cm² by 100 eV. Additional features originating from atomic nitrogen and NH (c-a) emissions were also observed. The NH (c-a) emissions accounted for about 8%, 13%, and 15% for total excited populations in collisions with Xe⁺, N⁺, and Kr⁺, respectively. These transitions were consistent with short-range interactions resulting in collision-induced dissociation of the NH₃ molecule with apparent energy thresholds between 20 and 30 eV and emission cross sections decreasing with ion mass. Evidence of charge exchange in the N⁺ + NH₃ collisions was observed in the resulting spectra as broad transitions between 420 and 480 nm and were assigned to NH⁺ emitting from the (B) state. Differences between the spectra were observed as changes in the emission signal with the neutral collisions producing only 30% or 65% of the NH (A-X) emission cross sections compared to the cation results for xenon and krypton, respectively. For N and N⁺, NH (A) was created in equal amounts at lower collision energies, but the emission for the neutral system increases above that of the cation at collision energies greater than 80 eV COM. In both cases, the threshold energy for appearance was below 10 eV, suggesting an additional pathway for NH (A) formation, namely, hydrogen abstraction or charge exchange and abstraction for the N and N⁺, respectively. In all cases, the neutral NH (c-a) emission intensity was similar between neutral and cation pairs. The H-α emission line (n = 3-2) decreased to about 10%, 33%, and 50% of the corresponding cation spectra for xenon, krypton, and nitrogen, respectively.

Luminescence measurements of hyperthermal Xe2+ + O2 and O+ + Xe collision systems

Emission excitation cross sections are recorded for collisions between Xe²⁺ + O₂ and O⁺ + Xe over a collision energy range of approximately 2 to 900 eV in the center-of-mass (E_cm) frame. Emissive products of the O⁺ + Xe reaction are examined in the 700-1000 nm optical range and include neutral atomic oxygen emissions and neutral xenon emissions. Atomic emission products of the O⁺ + Xe collision appear to have measureable cross sections near E_cm = 14 eV and increase in intensity until about E_cm = 60 eV where they remain approximately constant for the remainder of the measured collision energies. For the Xe²⁺ + O₂ collision system, O₂⁺ charge transfer products are measured through fluorescence of the O₂⁺(A-X) and (b-a) manifolds over the 200-850 nm window. Total cross sections for both manifolds do not vary beyond the experimental precision at all measured energies. Vibrational populations are derived from a fitting of the experimental data. The populations are found to deviate from a Franck-Condon distribution at all collision energies and appear to be well-modeled within a multi-channel Landau-Zener framework over the collision energy range measured.

Integral cross section measurements and product recoil velocity distributions of Xe(2+) + N2 hyperthermal charge-transfer collisions

Charge exchange from doubly charged rare gas cations to simple diatomics proceeds with a large cross section and results in populations of many vibrational and electronic product states. The charge exchange between Xe(2+) and N2, in particular, is known to create N2 (+) in both the A and B electronic states. In this work, we present integral charge exchange cross section measurements of the Xe(2+) + N2 reaction as well as axial recoil velocity distributions of the Xe(+) and N2 (+) product ions for collision energies between 0.3 and 100 eV in the center-of-mass (COM) frame. Total charge-exchange cross sections decrease from 70 Å(2) to about 40 Å(2) with increasing collision energy through this range. Analysis of the axial velocity distributions indicates that a Xe(2+) - N2 complex exists at low collision energies but is absent by 17.6 eV COM. Analysis of the axial velocity distributions reveals evidence for complexes with lifetimes comparable to the rotational period at low collision energies. The velocity distributions are consistent with quasi-resonant single charge transfer at high collision energies.

Chemi-luminescence measurements of hyperthermal Xe+/Xe2+ + NH3 reactions

Luminescence spectra are recorded for the reactions of Xe(+) + NH(3) and Xe(2+) + NH(3) at energies ranging from 11.5 to 206 eV in the center-of-mass (E(cm)) frame. Intense features of the luminescence spectra are attributed to the NH (A (3)Π(i)-X (3)Σ(-)), hydrogen Balmer series, and Xe I emission observable for both primary ions. Evidence for charge transfer products is only found through Xe I emission for both primary ions and NH(+) emission for Xe(2+) primary ions. For both primary ions, the absolute NH (A-X) cross section increases with collision energy before leveling off at a constant value, approximately 9 × 10(-18) cm(2), at about 50 eV while H-α emission increases linearly with collision energy. The nascent NH (A) populations derived from the spectral analysis are found to be independent of collision energy and have a constant rotational temperature of 4200 K.