Metastable Molecular Nitrogen Research Articles

The study of electronic kinetics of molecular nitrogen in the Titan’s middle atmosphere during the precipitation of cosmic rays

The kinetics of the \({{{\text{A}}}^{3}}\Sigma _{u}^{ + },\) B3Πg, W3Δu, \({{{\text{B}}}^{{{\text{'}}3}}}\Sigma _{u}^{ - },\) and C3Πu triplet states of molecular nitrogen at the heights of the middle atmosphere of Titan during action of cosmic rays into the atmosphere has been studied. The calculations consider the intramolecular and intermolecular electron energy transfer during inelastic collisions of electronically excited molecular nitrogen with N2, CH4, and CO molecules. The interaction of electronically excited N2 molecules with molecules of acetylene C2H2 and ethylene C2H4 in the middle atmosphere of Titan at altitudes of 50–250 km has been studied. For the first time, the dominance of reactions with metastable molecular nitrogen N2(\({{{\text{A}}}^{3}}\Sigma _{u}^{ + }\)) in the formation of C2H and C2H3 radicals at these heights has been shown.

Modeling Vibrational Populations of Metastable Molecular Nitrogen in Titan’s Atmosphere during the Precipitation of High-Energy Particles

Modeling Vibrational Populations of Metastable Molecular Nitrogen in Titan’s Atmosphere during the Precipitation of High-Energy Particles

Study of the Kinetics of Metastable Molecular Nitrogen in the Atmospheres of the Earth, Triton, Titan, and Pluto

In the interaction of high-energy electrons with gases of planetary atmospheres where the primary component is molecular nitrogen, a significant fraction of particle energy is spent on the excitation of electronically excited triplet states of N2. The processes of energy transfer from metastable molecular nitrogen $${{{\text{N}}}_{{\text{2}}}}\left( {{{{\text{A}}}^{{\text{3}}}}\Sigma _{{\text{u}}}^{ + }} \right)$$ to other components in the atmosphere of the Earth (a mixture of N2–O2–O gases), as well as in the atmospheres of Titan, Triton, and Pluto (a mixture of N2–CH4–CO gases), are considered. The paper discusses the processes in which metastable molecular nitrogen $${{{\text{N}}}_{{\text{2}}}}\left( {{{{\text{A}}}^{{\text{3}}}}\Sigma _{{\text{u}}}^{ + }} \right)$$ affects the kinetics of electronically excited atomic and molecular oxygen in the auroral ionosphere of the Earth. In addition, it is shown numerically for the first time that the contribution of $${{{\text{N}}}_{{\text{2}}}}\left( {{{{\text{A}}}^{{\text{3}}}}\Sigma _{{\text{u}}}^{ + }} \right)$$ to the formation of electronically excited carbon monoxide CO(a3Π) increases significantly with increasing density in the atmospheres of Titan, Triton, and Pluto, and becomes predominant for the lower vibrational levels of CO(a3Π).

The influence of metastable molecular nitrogen N2(A3Σu+) on the electronic kinetics of CO molecules

The simulation of N2(A3Σu+) and CO(a3Π) vibrational populations at the altitudes of Titan’s upper atmosphere and for conditions of a laboratory discharge in the N2-CO mixture is made. The influence of metastable molecular nitrogen N2(A3Σu+) on the electronic excitation of CO molecules in inelastic collisions is studied. It is shown that the increase in the density of the Titan’s atmosphere and of the discharge mixture leads to more significant excitation of lowest vibrational levels of CO(a3Π) by intermolecular electron energy transfers from N2(A3Σu+) in comparison with direct excitation of the a3Π state by free electrons.

Formation of simple nitrogen hydrides NH and NH2 at cryogenic temperatures through N + NH3→ NH + NH2 reaction: dark cloud chemistry of nitrogen.

Although NH3 molecules interacting with ground state nitrogen atoms N((4)S) seem not to be a very reactive system without providing additional energy to initiate the chemical process, we show through this study that, in the solid phase, at very low temperature, NH3 + N((4)S) reaction leads to the formation of the amidogen radical NH2. Such a dissociation reaction previously thought to occur exclusively through UV photon or energetic particle irradiation is in this work readily occurring just by stimulating the mobility of N((4)S)-atoms in the 3-10 K temperature range in the solid sample. The N((4)S)-N((4)S) recombination may be the source of metastable molecular nitrogen N2(A), a reactive species which might trigger the NH3 dissociation or react with ground state nitrogen atoms N((4)S) to form excited nitrogen atoms N((4)P/(2)D) through energy transfer processes. Based on our obtained results, it is possible to propose reaction pathways to explain the NH2 radical formation which is the first step in the activation of stable species such as NH3, a chemical induction process that, in addition to playing an important role in the origin of molecular complexity in interstellar space, is known to require external energy supplies to occur in the gas phase.

Intermolecular electron energy transfer processes in the collisions of N2(A3Σu+, v = 0–10) with CO and N2 molecules

The removal rates of metastable molecular nitrogen N2(A3Σu+, v=0–10) in the collisions with the ground state CO(X1Σ+, v=0–3) and N2(X1Σg+, v=0–3) molecules are calculated according to analytical expressions. The study includes a consideration of intermolecular electron energy transfers with the electronic excitation of target molecules. Reasonable agreement of the calculated rate coefficients with data of experimental measurements is obtained.

High temperature limitations for GaN growth by RF‐plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, and excess Ga‐overpressure

Growth of GaN by molecular beam epitaxy is limited by reduced growth rate related to thermal decomposition. Factors influencing thermal decomposition are growth species (atomic versus metastable molecular nitrogen), surface polarity (N- vs. Ga-polar), and varying Ga-overpressure. Surface polarity and growth species are the predominant influence determining the onset of thermal decomposition. A significant Ga-overpressure can suppress decomposition, allowing an increase in growth temperatures. Electrical properties are strongly influenced by Ga-overpressure and thermal decomposition. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High temperature limitations for GaN growth by rf-plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, hydrogen, and excess Ga-overpressure

The temperature used for growth of GaN by molecular beam epitaxy is ultimately limited by the greatly reduced growth rate related to thermal decomposition. This limiting temperature apparently varies from group to group. Factors influencing thermal decomposition are growth species (atomic versus metastable molecular nitrogen), surface polarity (N- versus Ga-polar), the presence of atomic hydrogen, and varying Ga-overpressure. Surface polarity and growth species are the predominant influence determining the onset of thermal decomposition. There are indications that the use of a significant Ga-overpressure can suppress decomposition allowing for an increase in obtainable growth temperatures for a given polarity. Electrical properties are shown to be strongly influenced by Ga-overpressure and thermal decomposition.

Production yields of H(D) atoms in the reaction of N2(a g,ν=0) with H2 and D2

Abstract Quantum yields for the production of H(D) atoms in the reaction of singlet-excited metastable molecular nitrogen, N2(a 1 Π g, ν=0), with H2 and D2 were determined by analyzing the temporal profiles of N2(a, ν=0) and H(D)-atom densities after pulsed excitation. N2(a, ν=0) was produced by the two-photon excitation of ground-state N2, while H(D) atoms were detected by two-photon laser-induced fluorescence. N2(a, ν=0) was detected by laser-induced fluorescence utilizing the N2(b′ 1 Σ u+, ν=7) state as an upper-state. The H(D) atom yields are 0.5 ± 0.1 for H2 and 0.4 ± 0.1 for D2, suggesting that the near resonant relaxation to another metastable molecular nitrogen, N2(a′ 1 Σ u−), is also important. The production of N2(a′ 1 Σ u−) in collisions with H2(D2) was confirmed by measuring the H2(D2) pressure dependence of the two-photon laser-induced fluorescence signal of N2(a′ 1 Σ u−, ν=0) via the N2(b 1 Π u, ν=1) state.

Corona discharge supersonic free-jet for III–V nitride growth via A 3Σu+ metastable nitrogen molecules

A corona discharge supersonic free-jet is shown to be a nearly pure source of A 3Σu+ metastable molecular nitrogen, an electronically excited and chemically active form of N2 that is ideally suited to nitride semiconductor growth. Optical emission spectroscopy at various distances downstream of the supersonic nozzle reveals a cascade through the excited state manifold of N2 triplet states to populate the A 3Σu+ state. Appearance potential spectroscopy (mass spectrometer electron bombardment ionization yield, measured as a function of electron impact energy) delivers the composition of the terminal molecular beam. A 3Σu+ molecules are the dominant activated species in the beam, which otherwise contains only nonreactive X 1Σg+ ground state nitrogen molecules plus a minor amount of S04 nitrogen atoms. Up to 1.56% number fraction of the beam is A 3Σu+, providing 1.0×1017 metastables sr−1 s−1.

Sample morphology and porosity in electron stimulated desorption: N2* from N2 adsorbed onto nanoscale ice films

We have measured the electron-stimulated desorption of metastable molecular nitrogen (N2*) from N2 condensed onto solid thin films of water of varying preparation. Structures seen in the N2* yield function permit the quantity of N2 at the film–vacuum interface to be monitored and hence allow one to study changes in the effective surface area of the water film. This latter quantity is itself related to the porosity of the film. When deposited onto porous water, N2 molecules penetrate into the film and throughout its pores covering their large surface area. Under these conditions, the signal of desorbing N2* particles is inversely proportional to the surface area of the pores. We present a simple model for N2 film growth on a porous film. Its mathematical formulation allows the pore area and pore volume of amorphous water films to be measured. The surface region of crystalline water films is also found to be rough. Moreover, the porosity of solid water films is found to be dependent on the substrate on which the film is grown.

Sample morphology and porosity in electron stimulated desorption: N2* from N2 adsorbed onto glassy and crystalline n-hexane

The electron-stimulated desorption of metastable molecular nitrogen (N2*) from N2 condensed onto n-hexane spacer films deposited on Pt(111) is investigated as a function of electron-impact energy (5–25 eV), and thickness (1–20 monolayers) and deposition temperature (T=20–80 K) of the n-hexane layer. At low T, the N2* yield is found to be inversely proportional to the thickness of the amorphous n-hexane layer. This behavior is explained by the existence of a porous structure in the n-hexane film which efficiently absorbs N2. The metastable signal is also strongly dependent on the temperature of n-hexane deposition, which controls the morphology of the spacer from amorphous at low T to crystalline at T>70 K. Increasing the deposition temperature of n-hexane from 20 to 70 K results in an increase of the N2* signal due to the decrease of the pore volume. Formation of the n-hexane layers in the crystalline state at higher temperatures further inhibits N2 migration into the spacer which results in further increases in the magnitude of the N2* desorption signal.

Influence of Active Nitrogen Species on the Nitridation Rate of Sapphire

The operating regimes of two rf-plasma sources, an Oxford CARS-25 and an EPI Unibulb, have been extensively characterized. By changing the exit aperture configuration and using an electrostatic deflector, the Oxford source could produce either primarily atomic nitrogen, atomic nitrogen mixed with low energy ions, or a large flux of higher energy ions (>65 eV) as the active species in a background of neutral molecular nitrogen. The EPI source produced a significant flux of metastable molecular nitrogen as the active species with a smaller atomic nitrogen component. Nitridation of sapphire using each source under the various operating conditions indicate that the reactivity was different for each type of active nitrogen. Boron contamination originating from the pyrolytic boron nitride plasma cell liner was observed.

Influence of Active Nitrogen Species on the Nitridation Rate of Sapphire

AbstractThe operating regimes of two rf-plasma sources, an Oxford CARS-25 and an EPI Unibulb, have been extensively characterized. By changing the exit aperture configuration and using an electrostatic deflector, the Oxford source could produce either primarily atomic nitrogen, atomic nitrogen mixed with low energy ions, or a large flux of higher energy ions (>65eV) as the active species in a background of neutral molecular nitrogen. The EPI source produced a significant flux of metastable molecular nitrogen as the active species with a smaller atomic nitrogen component. Nitridation of sapphire using each source under the various operating conditions indicate that the reactivity was different for each type of active nitrogen. Boron contamination originating from the pyrolytic boron nitride plasma cell liner was observed.

ChemInform Abstract: Observation of Discrete Trimethylsilylnitrene by Matrix‐Isolation Spectroscopy.

AbstractThe trimethylsilylnitrene radical, Me3SiN, has been produced by interaction of Me3SiN3 or Me3SiNCO with metastable molecular nitrogen or argon and has been trapped and observed directly in nitrogen and argon matrices.

Spectroscopy of matrix-isolated methylnitrene

The methylnitrene radical CH3N has been produced by the interaction of metastable molecular nitrogen and methylazide, and has been trapped in solid nitrogen at 10 K. The IR and UV absorption spectra are consistent with gas phase emission results, and also show transitions to several additional vibrational levels in the A 3E excited electronic state. The UV band system consists chiefly of a progression in the C–N stretching mode, possibly complicated by additional unresolved vibrational structure. These observations indicate that the absence of extensive hot band structure in the gas phase work is not due to rapid dissociation or isomerization from the upper state, which is bound by at least 3500 cm−1. The ESR signals previously attributed to CH3N cannot be produced under the same experimental conditions, but require additional photolysis. This observation suggests that a reexamination of previous ESR data is warranted.

Formation and quenching of metastable molecular nitrogen A3.SIGMA.u+ in the electronic relaxation of nitric oxide C2.PI. and D2.SIGMA.+ in a nitric oxide/nitrogen mixture

Time-resolved experiments are carried out to elucidate the electronic relaxation mechanism of NO C/sup 2/PI (or D/sup 2/..sigma../sup +/) + N/sub 2/ ..-->.. NO A/sup 2/..sigma../sup +/ + N/sub 2/, following the selective SVL excitation by two-photon absorption. The fluorescence intensity-time profiles of NO A/sup 2/..sigma../sup +/ formed collisionally show that the relaxation involves metastable N/sub 2/A/sup 3/..sigma../sub u//sup +/ as an intermediate in the energy transfer sequence of NO C/sup 2/PI (or D/sup 2/..sigma../sup +/) + N/sub 2/X..sigma../sub g//sup +/ ..-->.. NO X/sup 2/PI + N/sub 2/A/sup 3/..sigma../sub u//sup +/(1) and N/sub 2/A/sup 3/..sigma../sub u//sup +/ + NO X/sup 2/PI ..-->.. N/sub 2/X/sup 1/..sigma../sub g//sup +/ + NO A/sup 2/..sigma../sup +/ (2). The second energy transfer (process 2) rate controls the NO A/sup 2/..sigma../sup +/ fluorescence decay measured in NO/N/sub 2/ mixtures. The quenching rate constant of N/sub 2/AElt. slash/sub u//sup +/ by NO in the ground state has been determined to be (6.9 +- 0.7) x 10/sup -11/ cm/sup 3/ molecule/sup -1/ s/sup -1/ at 298 +- 3 K.

Resonances in the Metastable Excitation of Molecular Nitrogen

The excitation function for metastable molecular nitrogen has been studied over the electron-impact energy range 7-14 eV with an energy resolution of 0.05 eV. No resonances were observed below 11.8 eV in the $A^{3}\ensuremath{\Sigma}_{u}^{+}$ and $a^{1}\ensuremath{\Pi}_{g}$ channels. There is a sharp resonance at the threshold of the metastable $E^{3}\ensuremath{\Sigma}_{g}^{+}$ with a peak at 12.00 eV. Smaller structures were seen at 12.14 and 12.25 eV. A series of five resonances were observed at 12.59, 12.80, 13.03, 13.24, and 13.52 eV presumably in one or both of the $A^{3}\ensuremath{\Sigma}_{u}^{+}$ and $a^{1}\ensuremath{\Pi}_{g}$ channels. These confirm some of the structures observed in a recent transmission experiment. On the basis of the spacings and relative intensities of these resonances, a possible assignment for them is a temporary state of $N_{2}^{}{}_{}{}^{\ensuremath{-}}$ consisting of two Rydberg electrons around a core state $A^{2}\ensuremath{\Pi}_{u}$ of $N_{2}^{}{}_{}{}^{+}$.