The vacuum ultraviolet spectra of HCN,C2N2, and CH3CN

Quantitative vacuum ultraviolet absorption spectra for HCN, C₂N₂, and CH₃CN have been obtained over the wavelength range 60 nm ? λ ? 160 nm. Where comparison is possible, our measurements of the absorption coefficients for HCN and C₂N₂ are consistent with previous studies. Because of the superior resolution of this work (0.05 nm), vibrational assignments in the valence and Rydberg transitions of HCN have been extended while higher members of the Rydberg series in CH₃CN have been identified.     

The microwave spectra of cyanamide: Conclusions from a transitions

Microwave spectra have been observed for the species NH₂CN, NHDCN, ND₂CN, ¹⁵NH₂CN, NH₂C¹⁵N, ¹⁵ND₂CN and ND₂C¹⁵N. The nonplanar nature of the molecule is confirmed and the following structural parameters obtained N₁N₂ = 2.506 ± 0.002 Å, N₁C = 1.346 ± 0.005 Å, CN₂ = 1.160 ± 0.005 Å, N₁H = 1.001 ± 0.015 Å, HN?₁H = 113°31′ ± 2°, out of plane angle (see text) = 37°58′ ± 1°. (N₁ is the amino nitrogen atom and N₂ that the cyanide group.)     

Spectral study of reactions involving organic vapours and the pink afterglow of nitrogen

Chemiluminescent reactions resulting from addition of C₂H₂ and BrCN to nitrogen showing a pink afterglow have been investigated. The spectra show CN(B→A), CN(B→X), CN(A→X), and N₂(IIP) bands. The CN(B→X) bands are intense and exhibit abnormal rotational distributions with two rotational temperatures (T₁ = 2400°K, T₂ = 400°K). New perturbations and high-J rotational lines are reported. Comparisons of intensities of bands of the CN(B→A) and (B→X) systems yield 1:80 as the ratio of electronic transition probabilities for the two systems.     

Temperatures in a hollow-catmode discharge

Rotational and vibrational temperatures of He, O₂. and CO₂have been examined in carbon and molybdenum cathodes as functions of pressure and discharge current. The rotational temperature is strongly dependent on the conditions. The rotational temperatures of CO⁺, N ₂ ⁺ , C₂, CN, and OH are identical in simultaneous measurements.     

The chemistry of dimethyltetrazine on Pt(111)

As part of a program to further document the chemistry of CN on transition metal surfaces we have studied the decomposition of dimethyltetrazine on Pt(111). Products of the decomposition of dimethyltetrazine are H₂, N₂, HCN, C₂N₂ and small amounts of CH₃CN. Most of the methyl groups (>90%) are totally dehydrogenated leaving residual carbon on the surface. At low coverage the initial decomposition is CH bond cleavage. At higher coverage direct production of molecular N₂ at ~30°C is observed as the initial decomposition mode. Pretreatment of the Pt with H₂, shifts the high coverage decomposition to higher temperatures. Changes in the decomposition with coverage is explained as due to a change in bonding geometry. We suggest that at low coverage the molecular plane is parallel to the surface with the methyl groups in proximity to the surface, while at high coverage the molecule bonds on edge possibly through two adjacent nitrogens.     

Gas pressure effects on the structure of CNx thin films deposited by laser ablation

Carbon nitride thin films with different nitrogen concentration have been deposited at different N₂ and N₂/Ar mixed partial pressures. Time-integrated optical emission spectroscopy measurements have been performed to gather information on the nature of the chemical species present in the plasma. Both the CN and C₂ molecular species have been observed. Fast photography imaging of the expanding plume revealed the change of the dynamics from a free expansion at low pressure to a shock wave formation followed then by the plume stopping upon increasing the gas pressure values. Raman and XPS spectroscopy measurements performed on the deposited thin films revealed that the films, structure strongly depends on the dynamics of the expansion plasma regime rather than on the partial pressure at which the deposition takes place.     

Studies of R.F. discharges at moderate pressures and chemical applications—II. Nitrogen-hydrogen,nitrogen-methane and nitrogen-methane-hydrogen mixtures

Simultaneous vibro-rotational analyses have been carried out for the second positive system (SPS) of N₂ (C³П_u ? B³П_g), for the violet system (VS) of CN (B²Σ ? X²Σ) and for the Swan system (SS) of C₂ (d³П_g ? a³П_u), emitted by 35 MHz electrical discharges, containing N₂, H₂ and CH₄ flowing mixture s, in the 5–40 torr pressure range and at 1–10 Wcm^-3 power densities. The results are consistent with a Boltzman distribution for the rotational levels, but they show a deviation from this law for upper vibrational levels of CN and C₂.     

EPR and optical absorption studies of Cu<Superscript>2+</Superscript> ions in [ZnPd(CN)<Subscript>4</Subscript>(C<Subscript>4</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O<Subscript>2</Subscript>)] single crystals

A Cu²⁺-doped single crystal of catena-trans-bis(N-(2-hydroxyethyl)-ethylenediamine) zinc(II)-tetra-m-cyanopaladate(II) [ZnPd(CN)₄(C₄H₁₂N₂O₂)] complex has been investigated by electron paramagnetic resonance (EPR) technique at room temperature. EPR spectra indicate that Cu²⁺ ions substitute for magnetically equivalent Zn²⁺ ions and form octahedral complexes in [ZnPd(CN)₄(C₄H₁₂N₂O₂)] hosts. The crystal field affecting the Cu²⁺ ion is nearly axial. The optical absorption studies show two bands at 322 nm (30864 cm⁻¹) and 634 nm (15337 cm⁻¹) which confirm the axial symmetry. The spin Hamiltonian parameters and the relevant wave function are determined.     

ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.     

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C₃F₇CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF₆ environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C₂F₅CN, CF₃CN, COF₂ and CF₄ with the aluminium widely used in electrical equipment. It was found that the interaction between C₂F₅CN, CF₃CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF₂, CF₄ and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C₃F₇CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C₃F₇CN decomposition products and aluminium.     

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si 〈1 0 0〉 by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.     

Effect of oxygen on CN bands emitted from active nitrogen flames

O₂ and C₂H₂ are added to the reacting N₂ afterglow + C₂H₂ which emits intense CN bands. The resulting changes in the spectra are examined. The results are presented and explained on the basis of C + O₂ → CO + O and N + O₂ → NO + O.     

Vibrational spectroscopy at very high pressures. part 34.1 Raman spectra of polymorphs of mercuric cyanide

Phase transitions have been observed in mercuric cyanide near 2.5, 8, 19 and 60 kbar. The first four phases have been characterized by Raman spectroscopy. Phase II is closely related to the molecular parent phase I. The coordination at mercury appears to increase to four on entering phase III and phase IV has a spectrum consistent with the cubic structure related to anti-cuprite adopted at s.t.p. by Cd(CN)₂. Above 60 kbar deep brown Hg(CH)₂ V is formed irreversibly: it contains C =N rather than C≡N bonds.     

Laser plasma plume kinetic spectroscopy of the nitrogen and carbon species

The formation and decay of carbon and nitrogen atoms, CN radicals and C₂ molecules were monitored using spatial‐ and time‐resolved emission spectroscopy in a plasma plume formed during laser ablation of a graphite target in nitrogen atmosphere. A simple exponential model was used to explain the effect of the individual chemical reactions and plasma dynamics on the measured kinetic characteristics. The succession of emissions C → N → CN was observed in the time‐resolved spectra, supporting the suggestion that the CN radical is formed mainly by the direct reaction C + N → CN or C₂ + N₂ → 2CN. The formation of CN radical was enhanced by the additional generation of atomic nitrogen through the RF discharge. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Intensities,half-widths and shapes of spectral lines in the fundamental band of CO at low temperatures

Intensities and half-widths of spectral lines in the R-branch of the C¹²O¹⁶ fundamental band have been measured at 200, 150, 99, and 81 K. The broadeners used were CO, N₂, O₂, and CO₂. The validity of some representative theories relevant to these line parameters have been examined in the light of the present results. We also discuss the shape of CO lines at low temperatures.     

AP/(N2 + C2H2 + C2H4) gaseous fuel diffusion flame studies

Counterflow diffusion flame experiments and modeling results are presented for a fuel mixture consisting of N₂, C₂H₂, and C₂H₄ flowing against decomposition products from a solid AP pellet. The flame zone simulates the diffusion flame structure that is expected to exist between reaction products from AP crystals and a hydrocarbon binder. Quantitative species and temperature profiles have been measured for one strain rate, given by a separation of 5 mm, between the fuel exit and the AP surface. Species measured include C₂H₂, C₂H₄, N₂, CN, NH, OH, CH, C₂, NO, NO₂, O₂, CO₂, H₂, CO, HCl, H₂O, and soot volume fraction. Temperature was measured using a combination of a thermocouple at the fuel exit and other selected locations, spontaneous Raman scattering measurements throughout the flame, NO vibrational populations, and OH rotational population distributions. The burning rate of the AP was also measured for this flame’s strain rate. The measured eighteen scalars are compared with predictions from a detailed gas-phase kinetics model consisting of 105 species and 660 reactions. Model predictions are found to be in good agreement with experiment and illustrate the type of kinetic features that may be expected to occur in propellants when AP particles burn with the decomposition products of a polymeric binder.     

An experimental and kinetic modeling study of a premixed nitromethane flame at low pressure

A premixed nitromethane/oxygen/argon flame at low pressure (4.67 kPa) has been investigated using tunable vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. About 30 flame species including hydrocarbons, oxygenated and nitrogenous intermediates have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of the flame species have been determined by scanning burner position at some selected photon energies. The results indicate that N₂ and NO are the major nitrogenous products in the nitromethane flame. Compared with previous studies on nitromethane combustion, a number of unreported intermediates, including C₃H₄, C₄H₆, C₄H₈, C₂H₂O, C₂H₄O, CH₃CN, H₂CNHO, C₃H₃N and C₃H₇N, are observed in this work. Based on our experimental results and previous modeling studies, a detailed oxidation mechanism including 69 species and 314 reactions has been developed to simulate the flame structure. Despite some small discrepancies, the predictions by the modeling study are in reasonable agreement with the experimental results.     

DC discharge experiment in an Ar/N2/CO2 ternary mixture: A laboratory simulation of the Martian ionosphere's plasma environment

A low-pressure DC plasma discharge sustained in a 1.6%Ar–2.7%N₂–95.3%CO₂ ternary mixture is studied. This plasma was generated in a total pressure range from 1.0 to 4.0 Torr, a power of 6.3 W and a 12 l/min flow rate of gases. The electron temperature was found to be 8.41 eV and the ion density, in the order of 10⁹ cm⁻³. The species observed in the plasma mixture were CO₂, CO₂⁺, CN, CO, CO⁺, O₂, O₂⁺, N₂, N₂⁺, NO, C⁺, Ar and Ar⁺. At the pressure range in the present study, the species observed do not change their intensity due to an increase in the pressure and they separate in two groups according to their emission intensity: the band of the first group (CO₂, CO₂⁺ and CN) is approximately a factor of 3 more intense than that of the second group (CO, CO⁺, O₂, O₂⁺, N₂, N₂⁺, NO, C⁺, Ar and Ar⁺). The behavior of the emission intensities may be correlated to the constant ion density and electron temperature measured. Also, we observed the same constant behavior in the ratios of the neutral and positive species intensities to that of the N₂ intensity, as a function of pressure. This may suggest that the different rate coefficients and cross sections of elastic collision, excitation and de-excitation of electronic or vibrational levels, inelastic and superelastic collisions of electrons with the gas phase and products, neutral–neutral interactions, resonant charged transfer processes, recombination, to mention some, to produce these species change in the same proportion, as a function of the pressure to keep the relative ratios of the species almost constant.     

Infrared laser spectroscopy of the CN free radical in a methane-nitrogen-hydrogen plasma

Many Pand R-branch lines of the fundamental bands of the ¹²C¹⁴N and ¹³C¹⁴N radicals in their ground (²Σ⁺) electronic state have been measured at high resolution by diode laser absorption spectroscopy. The radicals were generated in a 2.45 GHz planar microwave plasma in methane with varying proportions of N₂ and H₂. From a fit to the spectra the origins of the fundamental bands of the two isotopomers were determined to be 2042.42104(84) cm^?1 and 2000.084 70(30) cm^?1. The main product detected in the plasma by diode laser spectroscopy is HCN, with concentrations about three orders of magnitude higher than CN.     

Crystal field effects on the magnetic and hyperfine properties of Yb3+ in ytterbium ethylsulfate

The magnetic and hyperfine properties of Yb³⁺ in Yb(C₂H₅SO₄)₃·.9H₂O have been studied using the crystal field (CF) obtained from an analysis of the observed absorption spectra of the crystal. The principal magnetic susceptibilities are in reasonable agreement with those observed both at liquid oxygen and liquid helium temperatures. The observed reversal of magnetic anisotropy at 17.7K is also corroborated. The Schottky heat capacity shows a peak at around 40K. The magnetic hyperfine field due to the 4f electrons at the nucleus is found to be 1.79MG. The hyperfine heat capacity C_N has a Schottky anomaly at about 25 mK. Above 1K, in the liquid helium range, C_N follows a simple T^?2 law as observed by Cooke et al. It is concluded that in the rare earth ethylsulfates a single suitable CF gives a good account of the various properties from room temperature down to liquid He temperatures.