High-Energy Quantum Dynamics of the 15N + o-14N14N Rovibrational Activation and Isotope Exchange Processes

We report full quantum reaction probabilities, computed within the framework of time-independent quantum mechanics using hyperspherical coordinates, for the 15N + 14N14N inelastic and reactive collision processes, restricted to total angular momentum J = 0, for kinetic energies up to 4.5 eV. We take advantage of the nonzero (i = 1) nuclear spin of 14N, leading to the existence of two nuclear spin isomers of 14N14N, namely, ortho- and para-14N14N, to restrict the study to the ortho molecular nitrogen species, with even rotational quantum number j = 0, 2, ... states. Specifically, we start with diatomic reagents ortho-14N14N in the initial rotational state j = 0. A comparison with similar works previously published by other groups using time-dependent wave packet and quasi-classical trajectory methods for the 14N + 14N14N fully symmetric collision is given. We find that reactive processes 15N + 14N14N involving atom exchange do not happen for collision energies less than 2.2 eV. Collisions at energies of around 2.0 eV are most effective for populating reactants' rovibrational states, that is, for inelastic scattering, whereas those at energies close to 5.0 eV yield a newly formed 14N15N isotopologue in a wide variety of excited vibrational levels.

Vibrational kinetics in repetitively pulsed atmospheric pressure nitrogen discharges: average-power-dependent switching behaviour

Characterisation of the vibrational kinetics in nitrogen-based plasmas at atmospheric pressure is crucial for understanding the wider plasma chemistry, which is important for a variety of biomedical, agricultural and chemical processing applications. In this study, a 0-dimensional plasma chemical-kinetics model has been used to investigate vibrational kinetics in repetitively pulsed, atmospheric pressure plasmas operating in pure nitrogen, under application-relevant conditions (average plasma powers of 0.23-4.50 W, frequencies of 1-10 kHz, and peak pulse powers of 23-450 W). Simulations predict that vibrationally excited state production is dominated by electron-impact processes at lower average plasma powers. When the average plasma power increases beyond a certain limit, due to increased pulse frequency or peak pulse power, there is a switch in behaviour, and production of vibrationally excited states becomes dominated by vibrational energy transfer processes (vibration-vibration (V-V) and vibration-translation (V-T) reactions). At this point, the population of vibrational levels up to v ⩽ 40 increases significantly, as a result of V-V reactions causing vibrational up-pumping. At average plasma powers close to where the switching behaviour occurs, there is potential to control the energy efficiency of vibrational state production, as small increases in energy deposition result in large increases in vibrational state densities. Subsequent pathways analysis reveals that energy in the vibrational states can also influence the wider reaction chemistry through vibrational-electronic (V-E) linking reactions (N + N2 ( 40 ⩽ v ⩽ 45 ) → N( 2 D ) + N2 ( A ) and N + N2 ( 39 ⩽ v ⩽ 45 ) → N + N2 ( a ' ) ), which result in increased Penning ionisation and an increased average electron density. Overall, this study investigates the potential for delineating the processes by which electronically and vibrationally excited species are produced in nitrogen plasmas. Therefore, potential routes by which nitrogen-containing plasma sources could be tailored, both in terms of chemical composition and energy efficiency, are highlighted.

THE PRESENCE OF EXCITED MOLECULES IN ACTIVE NITROGEN

Spectra of active nitrogen have been photographed under conditions comparable to those used for most studies of reactions of active nitrogen with other molecules. Bands observed were identified as the first positive system of nitrogen and the β- and γ-bands of nitric oxide. No trace of Vegard–Kaplan emission was observed. The 2 537 line of mercury was detected under certain conditions.The results are used to rationalize the large discrepancy which exists between estimates of the lifetime of N2(A3Σu+) by optical spectroscopy and reaction kinetics. In the former method, the measurements are performed in an oxygen-free system and are clearly related to a radiative lifetime. In the latter method, the measurements are performed in the presence of traces of oxygen and are believed to indicate a collisional lifetime. The reaction kinetic measurements are shown to be in complete agreement, both with regard to decay kinetics and lifetime, with electron spin resonance measurements on active nitrogen produced under near-identical conditions.

CHEMICAL SCAVENGER PROBE STUDIES OF ATOM AND EXCITED MOLECULE REACTIVITY IN ACTIVE NITROGEN FROM A SUPERSONIC STREAM

A quartz chemical scavenger probe has been developed to study the local composition of supersonic electrically discharged gas streams. The probe samples the central portion of a nonequilibrium jet and allows direct comparison with other local measurement techniques (e.g. differential catalytic detectors) for determining active species concentrations. Active nitrogen from a Mach 3 stream was sampled and reacted inside the probe with one of the scavenger gases NO, NH3, or C2H4at 18.8 mm Hg and at an average temperature of 500 °K. Limiting values of the NO destruction rate and the HCN production rate were observed; however, NH3destruction exhibited no plateau. The observed maximum rate of NO destruction was 2.1 times as large as the NO flow rate at the light titration end-point. This difference is attributed to a reaction of NO, added in excess of the titration end-point flow, with metastable electronically excited molecules formed within the discharge zone. The converging-diverging supersonic nozzle-glow discharge source used in these experiments apparently delivers metastable excited molecules to the reaction zone in a higher relative concentration than do the more conventional subsonic electrical discharge flow systems used for most previous active nitrogen studies.