Dynamics of gas phase Ne${}^{\ast }$ + NH${}_3$ and Ne${}^{\ast }$ + ND${}_3$ Penning ionization at low temperatures

Abstract

Two isotopic chemical reactions, ${\mathrm{Ne}}^{\ast }$ + NH${}_3$, and ${\mathrm{Ne}}^{\ast }$ + ND${}_3$, have been studied at low collision energies by means of a merged beams technique. Partial cross sections have been recorded for the two reactive channels, namely ${\mathrm{Ne}}^{\ast }$ + NH${}_3$ $\to$ Ne + NH${}_3^{+}$ + $e^{-}$, and ${\mathrm{Ne}}^{\ast }$ + NH${}_3$ $\to$ Ne + NH${}_2^{+}$ + H + $e^{-}$, by detecting the NH${}_3^{+}$ and NH${}_2^{+}$ product ions, respectively. The cross sections for both reactions were found to increase with decreasing collision energy, $E_{coll}$, in the range 8 $\mu$eV$<E_{coll}<$ 20 meV. The measured rate constant exhibits a curvature in a log(k)-log($E_{coll}$) plot from which it is concluded that the Langevin capture model does not properly describe the ${\mathrm{Ne}}^{\ast }$ + NH${}_3$ reaction in the entire range of collision energies covered here. Calculations based on multichannel quantum defect theory were performed to reproduce and interpret the experimental results. Good agreement was obtained by including long range van der Waals interactions combined with a 6-12 Lennard-Jones potential. The branching ratio between the two reactive channels, $\Gamma =\frac{[N{H}_2^{+}]}{[N{H}_2^{+}]+[N{H}_3^{+}]}$, is relatively constant, $\Gamma \approx 0.3$, in the entire collision energy range studied here. Possible reasons for this observation are discussed and rationalised in terms of relative time scales of the reactant approach and the molecular rotation. Isotopic differences between the ${\mathrm{Ne}}^{\ast }$ + NH${}_3$ and ${\mathrm{Ne}}^{\ast }$ + ND${}_3$ reactions are small, as suggested by nearly equal branching ratios and cross sections for the two reactions.

References in corpus (3)

• Observation of Quantum Effects in sub Kelvin Cold Reactions
• Large Effects of Electric Fields on Atom-Molecule Collisions at Millikelvin Temperatures
• Study of the Ne(^3P_2) + CH_3F Electron Transfer Reaction below 1 Kelvin

Cited by in corpus (13)

• Observation of enhanced rate coefficients in the H${}_2^{+}$ + H${}_2$ $\to$ H${}_3^{+}$ + H reaction at low collision energies
• Observation of orbiting resonances in He(3S1) + NH3 Penning ionization
• Energy dependent stereodynamics of the Ne(${}^3$P${}_2$)+Ar reaction
• Study of the Ne(^3P_2) + CH_3F Electron Transfer Reaction below 1 Kelvin
• Quantum state resolved molecular dipolar collisions over four decades of energy
• Ion-molecule reactions below 1~K: Observation of a strong enhancement of the reaction rate of the ion-dipole reaction He${}^{+}$+ CH${}_3$F
• Statistical product distributions for ultracold reactions in external fields
• Multipole-moment effects in ion-molecule reactions at low temperatures: part I -- Ion-dipole enhancement of the rate coefficients of the He${}^{+}$ + NH${}_3$ and He${}^{+}$ + ND${}_3$ reactions at collision energies near $0$ K
• Quantum defect model of a reactive collision at finite temperature
• Molecular Collisions: from Near-cold to Ultra-cold
• Zeeman deceleration of electron-impact-excited metastable helium atoms
• Beyond universality: parametrizing ultracold complex-mediated reactions using statistical assumptions
• Universal behavior in complex-mediated reactions: Dynamics of S(1D)+ o-D2 --> D + SD at low collision energies