Dissociation Of N2 Research Articles

Energy-related catalysis

by addition of alkali metals as promoters [13] Adding alkali(oxides) to the surface of a transition-metal induces local electrical fields.This allows one to exploit the fact that the N2 dissociation transition state has a larger dipole moment than adsorbed N. Therefore, the scaling relation line in Fig. 1a is shifted downwards resulting in a circumvention of the pure-metal scaling relation and a considerably better catalyst.These industrial advancements can be contrasted to the naturally occurring systems as enzymes including nitrogenase. Despite that this biological system is known to be able to make ammonia at ambient temperatures and pressure, it is a very inefficient process. Hence, not only do we need to find inorganic catalyst but they have to be scalable andmore efficient than the naturally occurring process. The challenge remains to develop a systematic approach to understanding effects like this in order to give us a toolbox of strategies to design radically better catalysts. ACKNOWLEDGEMENTS

Prevalence of Bimolecular Routes in the Activation of Diatomic Molecules with Strong Chemical Bonds (O2, NO, CO, N2) on Catalytic Surfaces.

Dissociation of the strong bonds in O2, NO, CO, and N2 often involves large activation barriers on low-index planes of metal particles used as catalysts. These kinetic hurdles reflect the noble nature of some metals (O2 activation on Au), the high coverages of co-reactants (O2 activation during CO oxidation on Pt), or the strength of the chemical bonds (NO on Pt, CO and N2 on Ru). High barriers for direct dissociations from density functional theory (DFT) have led to a consensus that "defects", consisting of low-coordination exposed atoms, are required to cleave such bonds, as calculated by theory and experiments for model surfaces at low coverages. Such sites, however, bind intermediates strongly, rendering them unreactive at the high coverages prevalent during catalysis. Such site requirements are also at odds with turnover rates that often depend weakly on cluster size or are actually higher on larger clusters, even though defects, such as corners and edges, are most abundant on small clusters. This Account illustrates how these apparent inconsistencies are resolved through activations of strong bonds assisted by co-adsorbates on crowded low-index surfaces. Catalytic oxidations occur on Au clusters at low temperatures in spite of large activation barriers for O2 dissociation on Au(111) surfaces, leading to proposals that O2 activation requires low-coordination Au atoms or Au-support interfaces. When H2O is present, however, O2 dissociation proceeds with low barriers on Au(111) because chemisorbed peroxides (*OOH* and *HOOH*) form and weaken O-O bonds before cleavage, thus allowing activation on low-index planes. DFT-derived O2 dissociation barriers are much lower on bare Pt surfaces, but such surfaces are nearly saturated with CO* during CO oxidation. A dearth of vacant sites causes O2* to react with CO* to form *OOCO* intermediates that undergo O-O cleavage. NO-H2 reactions occur on Pt clusters saturated with NO* and H*; direct NO* dissociation requires vacant sites that are scarce on such surfaces. N-O bonds cleave instead via H*-assistance to form *HNOH* intermediates, with barriers much lower than for direct NO* dissociation. CO hydrogenation on Co and Ru occurs on crowded surfaces saturated with CO*; rates increase with increasing Co and Ru cluster size, indicating that low-index surfaces on large clusters can activate CO*. Direct CO*dissociation, however, occurs with high activation barriers on low-index Co and Ru surfaces, and even on defect sites (step-edge, corner sites) at high CO* coverages. CO* dissociation proceeds instead with H*-assistance to form *HCOH* species that cleave C-O bonds with lower barriers than direct CO* dissociation, irrespective of surface coordination. H2O increases CO activation rates by assisting H-additions to form *HCOH*, as in the case of peroxide formation in Au-catalyzed oxidations. N2 dissociation steps in NH3 synthesis on Ru and Fe are thought to also require defect sites; yet, barriers on Ru(0001) indicate that H*-assisted N2 activation - unlike O2, CO, and NO - is not significantly more facile than direct N2 dissociation, suggesting that defects and low-index planes may both contribute to NH3 synthesis rates. The activation of strong chemical bonds often occurs via bimolecular reactions. These steps weaken such bonds before cleavage on crowded low-index surfaces, thus avoiding the ubiquitous kinetic hurdles of direct dissociations without requiring defect sites.

A transformed framework for dynamic correlation in multireference problems.

We describe how multireference dynamic correlation theories can be naturally obtained as single-reference correlation theories in a canonically transformed frame. Such canonically transformed correlation theories are very simple and involve identical expressions to their single-reference counterparts. The corresponding excitations involve quasiparticles rather than the bare particles of the system. High-order density matrices (or their approximations) and the numerical metric instabilities common to multireference correlation theories do not appear. As an example, we formulate the Bogoliubov canonically transformed version of second-order Møller-Plesset perturbation theory and demonstrate its performance in H2, H2O, N2, and BeH2 bond dissociation.

Influence of the van der Waals interaction in the dissociation dynamics of N2 on W(110) from first principles.

Using ab initio molecular dynamics (AIMD) calculations, we investigate the role of the van der Waals (vdW) interaction in the dissociative adsorption of N2 on W(110). Hitherto, existing classical dynamics calculations performed on six-dimensional potential energy surfaces based on density functional theory (DFT), and the semi-local PW91 and RPBE [Hammer et al. Phys. Rev. B 59, 7413 (1999)] exchange-correlation functionals were unable to fully describe the dependence of the initial sticking coefficient on the molecular beam incidence conditions as found in experiments. N2 dissociation on W(110) was shown to be very sensitive not only to short molecule-surface distances but also to large distances where the vdW interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selection of existing non-local functionals that include the vdW interaction (vdW-functionals). Clearly, the inclusion of the non-local correlation term contributes in all cases to correct the unrealistic energy barriers that were identified in the RPBE at large molecule-surface distances. Among the tested vdW-functionals, the original vdW-DF by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and the ulterior vdW-DF2 give also an adequate description of the N2 adsorption energy and energy barrier at the transition state, i.e., of the properties that are commonly used to verify the quality of any exchange-correlation functional. However, the results of our AIMD calculations, which are performed at different incidence conditions and hence extensively probe the multi-configurational potential energy surface of the system, do not seem as satisfactory as the preliminary static analysis suggested. When comparing the obtained dissociation probabilities with existing experimental data, none of the used vdW-functionals seems to provide altogether an adequate description of the N2/W(110) interaction at short and large distances.

The dynamics of adsorption and dissociation of N2 in a monolayer of iron on W(110).

We study the adsorption dynamics of N2 on an expanded monolayer of Fe grown pseudomorphically on W(110). To this aim we have performed molecular dynamics simulations in a six-dimensional potential energy surface calculated within density functional theory. Our results show that N2 dissociation on this surface is a highly activated process with an energy barrier of around 1.25 eV. Regarding molecular adsorption, we find that the energetically most favorable adsorption well corresponds to a parallel orientation of the molecule with an adsorption energy of around 520 meV. However, at low molecular energies and surface temperatures, the molecules preferentially adsorb vertically to the surface with an adsorption energy of around 480 meV. A comparative analysis with the results previously obtained on a clean Fe(110) surface shows that while surface strain favors molecular adsorption of N2 in this system, it impedes dissociative adsorption. The former is consistent with the experimental observations showing that the inertness of Fe(110) towards N2 uptake is reduced in the strained surface. The latter leads us to suggest that the experimental observation of dissociated atomic N in the strained surface when increasing surface temperature must be related to the presence of step/defects at the surface.

On the mechanism of Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones: density functional theory survey

In this article, we have theoretically investigated the possible reaction mechanisms for Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones. The ωb97X-D method and C-PCM solvent model are used to describe the reaction processes. After the formation of allenylpalladium through C–O bond cleavage from propargylic carbonates, both decarboxylation and ligand exchange processes are explored. Then, depending on different conditions, we considered three possible types of reaction mechanisms, carbene insertion triggered by N2 release, C–C coupling reactions without N2 release, and C–C coupling reactions via the out-sphere attack of diazo compound. Our results indicate that it is favorable to undergo the carbene insertion into allenylpalladium after ligand exchange with diazo compound, which is partially agreement with the experimental suggestions. Although the decarboxylation is more difficult than ligand exchange, the reaction rate could be limited by Pd-catalyzed N2 dissociation from diazo compound. Additionally, it should be essential to select DFT-D method to describe this reaction.

Use of density functional theory orbitals in the GVVPT2 variant of second-order multistate multireference perturbation theory.

A new variation of the second-order generalized van Vleck perturbation theory (GVVPT2) for molecular electronic structure is suggested. In contrast to the established procedure, in which CASSCF or MCSCF orbitals are first obtained and subsequently used to define a many-electron model (or reference) space, the use of an orbital space obtained from the local density approximation (LDA) variant of density functional theory is considered. Through a final, noniterative diagonalization of an average Fock matrix within orbital subspaces, quasicanonical orbitals that are otherwise indistinguishable from quasicanonical orbitals obtained from a CASSCF or MCSCF calculation are obtained. Consequently, all advantages of the GVVPT2 method are retained, including use of macroconfigurations to define incomplete active spaces and rigorous avoidance of intruder states. The suggested variant is vetted on three well-known model problems: the symmetric stretching of the O-H bonds in water, the dissociation of N2, and the stretching of ground and excited states C2 to more than twice the equilibrium bond length of the ground state. It is observed that the LDA-based GVVPT2 calculations yield good results, of comparable quality to conventional CASSCF-based calculations. This is true even for the C2 model problem, in which the orbital space for each state was defined by the LDA orbitals. These results suggest that GVVPT2 can be applied to much larger problems than previously accessible.

The multifacet graphically contracted function method. I. Formulation and implementation.

The basic formulation for the multifacet generalization of the graphically contracted function (MFGCF) electronic structure method is presented. The analysis includes the discussion of linear dependency and redundancy of the arc factor parameters, the computation of reduced density matrices, Hamiltonian matrix construction, spin-density matrix construction, the computation of optimization gradients for single-state and state-averaged calculations, graphical wave function analysis, and the efficient computation of configuration state function and Slater determinant expansion coefficients. Timings are given for Hamiltonian matrix element and analytic optimization gradient computations for a range of model problems for full-CI Shavitt graphs, and it is observed that both the energy and the gradient computation scale as O(N(2)n(4)) for N electrons and n orbitals. The important arithmetic operations are within dense matrix-matrix product computational kernels, resulting in a computationally efficient procedure. An initial implementation of the method is used to present applications to several challenging chemical systems, including N2 dissociation, cubic H8 dissociation, the symmetric dissociation of H2O, and the insertion of Be into H2. The results are compared to the exact full-CI values and also to those of the previous single-facet GCF expansion form.

Reduction of State-to-State to Macroscopic Models for Hypersonics

Four different types of macroscopic models developed for the vibration-chemistry coupling in nonequilibrium flows for re-entry applications are presented. First, using an approach based on nonequilibrium thermodynamics, global rate coefficients of dissociation of N2 and O2 under parent molecular or atomic impact and backward molecular recombination are determined. Then a Two-Level Distribution (TLD) model is developed, in which a relaxation equation for vibrational temperature is solved as in the case of multi-temperature models but with the simultaneous solution of a kinetic equation, as in the case of state-to-state models, but only for the last vibrational level. In a third approach, a multi- internal temperature model is presented to describe accurately the vibrational distribution function in using several groups of levels, within which the levels are assumed to follow a Boltzmann distribution at an internal temperature of the group. This multi-internal temperature model allows us to describe accurately the vibrational energy relaxation and dissociation processes behind a strong shock wave. Finally, a rovibrational collisional coarse-grain model is developed to reduce a detailed rovibrational mechanism for the internal energy excitation and dissociation processes behind a strong shock wave in a nitrogen flow.

Rovibrational coupling in molecular nitrogen at high temperature: An atomic-level study

This article contains an atomic-level numerical investigation of rovibrational relaxation in molecular nitrogen at high temperature (>4000 K), neglecting dissociation. We conduct our study with the use of pure Molecular Dynamics (MD) and Classical Trajectory Calculations (CTC) Direct Simulation Monte Carlo (DSMC), verified to produce statistically identical results at the conditions of interest here. MD and CTC DSMC solely rely on the specification of a potential energy surface: in this work, the site-site Ling-Rigby potential. Additionally, dissociation is prevented by modeling the N–N bond either as a harmonic or an anharmonic spring. The selected molecular model was shown to (i) recover the shear viscosity (obtained from equilibrium pure MD Green-Kubo calculations) of molecular nitrogen over a wide range of temperatures, up to dissociation; (ii) predict well the near-equilibrium rotational relaxation behavior of N2; (iii) reproduce vibrational relaxation times in excellent accordance with the Millikan-White correlation and previous semi-classical trajectory calculations in the low temperature range, i.e., between 4000 K and 10 000 K. By simulating isothermal relaxations in a periodic box, we found that the traditional two-temperature model assumptions become invalid at high temperatures (>10 000 K), due to a significant coupling between rotational and vibrational modes for bound states. This led us to add a modification to both the Jeans and the Landau-Teller equations to include a coupling term, essentially described by an additional relaxation time for internal energy equilibration. The degree of anharmonicity of the N2 bond determines the strength of the rovibrational coupling. Although neglecting N2 dissociation only provides a partial description of a nitrogen system at very high temperatures, high-energy trends for bound-bound transitions are essential to understand nonequilibrium gas flows, with possible implications on rovibration/chemistry interaction at the onset of N2 dissociation.

N vacancy, substitutional O, and Al defects in the bandgap of composition-tunable nonstoichiometric AlN powder

AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN—ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level.

Quantum Monte Carlo for activated reactions at solid surfaces: Time well spent on stretched bonds

Many chemical reactions involve bond‐dissociation. This is also true for reactions at solid surfaces, in which the dissociation step is often limiting but facilitated in comparison to gas‐phase reaction channels. This work considers N2 dissociation. The molecule is strongly bound and stretched geometries are chosen. Heterogeneous catalysis by copper is simulated. It was investigated in our previous work as it is in many ways a prototype metal presenting a close‐packed surface here. These nitrogen molecules are adsorbed on copper and fixed geometries on the dissociation reaction pathway for stretched N2 are given using density functional theory (DFT) calculations in a plane‐wave basis. This dissociating molecule appears to be underbound using the ab initio Perdew, Burke, Ernzerhof (PBE) DFT functional but while this phenomenon accounts for a few percent at 5 Å, at 6 Å, PBE gives less than 30% of the binding energy. This indicates the onset of dissociation. The PBE wave‐functions at these bond‐lengths serve as trial input for Quantum Monte Carlo (QMC) simulations of the ground states to obtain highly accurate correlated results for the associated activation barriers indicating the catalytic effect on this dissociation. The geometries from this bond‐stretching study mimic the transition state (TS). This procedure requires no search for the actual TS geometry. Finite‐size effects and fixed‐node error are possible limitations to accuracy of this type of QMC study. We are able to limit fixed‐node error, using certain trial wave‐functions. The finite‐size effect is considerable, although comparing two adsorbed geometries cancels about 90% with respect to clean surfaces. Unfolding the cell to simulate a 9 k‐point grid (rather than a single k‐point) reduces the remainder by at least a factor 130 but relations for calibrating the remaining (2 mHa) error on converged grids are also used. The pseudopotential used to represent the atomic core of copper must also be determined carefully: we leave 11 active electrons but include the 3d shell in the pseudopotential. © 2014 Wiley Periodicals, Inc.

Exploring the limits: A low-pressure, low-temperature Haber–Bosch process

The Haber–Bosch process for ammonia synthesis has been suggested to be the most important invention of the 20th century, and called the ‘Bellwether reaction in heterogeneous catalysis’. We examine the catalyst requirements for a new low-pressure, low-temperature synthesis process. We show that the absence of such a process for conventional transition metal catalysts can be understood as a consequence of a scaling relation between the activation energy for N2 dissociation and N adsorption energy found at the surface of these materials. A better catalyst cannot obey this scaling relation. We define the ideal scaling relation characterizing the most active catalyst possible, and show that it is theoretically possible to have a low pressure, low-temperature Haber–Bosch process. The challenge is to find new classes of catalyst materials with properties approaching the ideal, and we discuss the possibility that transition metal compounds have such properties.

Collisions of low-energy Ar+, N2+, and D2+ ions with room-temperature and heated surfaces of mixed beryllium–tungsten thin films of different composition

Collisions of Ar+, N2+, and D2+ ions of incident energies 20–100eV with thin mixed beryllium–tungsten films of different composition (BeW(90:10); BeW(50:50); BeWO(60:22:11)) and different temperatures of the samples (room temperature, 150°C, 300°C) were investigated using a tandem mass spectrometer system. Mass spectra of product ions arising from Ar+ collisions with the three samples showed sputtering of the basic material of the sample substrate (Be+, BeH+, BeOH+; Li+, Na+, K+) and of hydrocarbon ions from the hydrocarbon coverage of the sample that decreased with increasing temperature. Sputtering of W+ or its compounds could not be detected. Normalized relative ion yields of Be+ and its compounds were not proportional to the Be content in the sample. Mass spectra from N2+ collisions were very similar to those of Ar+. Surface-induced dissociation of N2+ to N+ was not detected. The most conspicuous difference between mass spectra from D2+ impact and from Ar+ impact was a much lower sputtering efficiency of D2+ (by a factor of 50–100 or, for alkali ions, even more). The relative ion yield of Be+ strongly increased when the temperature of the sample was raised to 400°C and 450°C. A surface chemical reaction between the incident D2+ and surface Be leading to BeD+ was observed. The data may be of interest as basic information relevant to plasma–wall interactions in fusion devices.

Enhanced N2 Dissociation on Ru-Loaded Inorganic Electride

Electrides, i.e. salts in which electrons serve as anions, are promising materials for lowering activation energies of chemical reactions. Ab initio simulations are used to investigate the effect of the electron anions in a prototype mayenite-based electride (C12A7:e(-)) on the mechanism of N2 dissociation. It is found that both atomic and molecular nitrogen species chemisorb on the electride surface and become negatively charged due to the electron transfer from the substrate. However, charging alone is not sufficient to promote dissociation of N2 molecules. In the presence of Ru, N2 adsorbs with the formation of a cis-Ru2N2 complex and the N-N bond weakens due to both the electron transfer from the substrate and interaction with Ru. This complex transforms into a more stable trans-Ru2N2 configuration, in which the N2 molecule is dissociated, with the calculated barrier of 116 kJ mol(-1) and the overall energy gain of 72 kJ mol(-1). In contrast, in the case of the stoichiometric mayentie, the cis-Ru2N2 is ~34 kJ mol(-1) more stable than the trans-Ru2N2, while the cis-trans transition has a barrier of 192 kJ mol(-1). Splitting of N2 is promoted by a combination of the strong electron donating power of C12A7:e(-), ability of Ru to capture N2, polarization of Ru clusters, and electrostatic interaction of negatively charged N species with the surface cations.

High Energy Density Mixed Polymeric Phase from Carbon Monoxide and Nitrogen

Carbon monoxide and nitrogen are among the potentially interesting high-energy density materials. However, in spite of the physical similarities of the molecules, they behave very differently at high pressures. Using density functional theory and structural prediction methods, we examine the ability of these systems to combine their respective properties and form novel mixed crystalline phases under pressures of up to 100 GPa. Interestingly, we find that CO catalyzes the molecular dissociation of N2, which means mixed structures are favored at a relatively low pressure (below 18 GPa), and that a three-dimensional framework with Pbam symmetry becomes the most stable phase above 52 GPa, i.e., at much milder conditions than in pure solid nitrogen. This structure is dynamically stable at ambient pressure and has an energy density of approximately 2.2 kJ g(-1), making it a candidate for a high-energy density material, and one that could be achieved at less prohibitive experimental conditions.

Titan's atmosphere simulation experiment using continuum UV‐VUV synchrotron radiation

A new reactor, named APSIS for Atmospheric Photochemistry Simulated by Synchrotron, is designed for simulating the reactivity occurring in planetary upper atmospheres. In this reactor, a gas mixture roughly reproducing Titan's main atmosphere composition (N2/CH4 = 90/10) is irradiated by a continuous spectrum in the 60−350 nm range, provided by the DISCO beamline at the SOLEIL synchrotron radiation facility. This spectral range enables the dissociation and ionization of N2 and CH4, as observed in plasma reactors and Titan's ionosphere. The neutral products are detected in situ by quadrupole mass spectrometry and collected with a cryogenic trap for ex situ analysis by gas chromatography‐mass spectrometry. The detected reaction products include C2, C3, C4, and probably C5 organic compounds, with important amounts of nitrogen‐bearing species: HCN, CH3CN, and C2N2. Neutral mass spectra obtained with APSIS are compared with Ion and Neutral Mass Spectrometer experiments of the Cassini space probe in the upper Titan atmosphere and with other results of current Titan atmosphere chemistry laboratory simulations.

Kinetic Analysis of Dielectric Layer Thickness on Nitric Oxide Removal by Dielectric Barrier Discharge

The kinetic analysis of dielectric layer thickness on nitric oxide (NO) removal in dielectric barrier discharge (DBD) reactor was investigated. The simulated results show that, with the decrease of dielectric layer thickness, the electric field increases, leading to an enlarging E/N. When E/N was 250 Td, the dissociation rate and electron mean energy reached 14.3 times and 1.5 times respectively compared to when E/N was 150 Td, and their excitation rates were magnified 176, 182, 226, and 171% separately, generating more N atoms and metastable states of N2 molecules. In NO/N2 system, the dissociation and excitation rate of N2 were related to the amount of NO removal. The experimental results show that, NO removal efficiency increased as energy density was increased and a decreasing dielectric layer thickness promoted NO removal, which coincides with simulated ones well, indicating the feasibility and the rationality of the dynamics analysis.

Global sensitivity analysis for DSMC simulations of hypersonic shocks

Two global, Monte Carlo based sensitivity analyses were performed to determine which reaction rates most affect the results of Direct Simulation Monte Carlo (DSMC) simulations for a hypersonic shock in five-species air. The DSMC code was written and optimized with shock tube simulations in mind, and includes modifications to allow for the efficient simulation of a 1D hypersonic shock. The TCE model is used to convert Arrhenius-form reaction rate constants into reaction cross-sections, after modification to allow accurate modeling of reactions with arbitrarily large rates relative to the VHS collision rate. The square of the Pearson correlation coefficient was used as the measure for sensitivity in the first of the analyses, and the mutual information was used as the measure in the second. The quantity of interest (QoI) for these analyses was the NO density profile across a 1D shock at ∼8000m/s (M∞≈23). This vector QoI was broken into a set of scalar QoIs, each representing the density of NO at a specific point downstream of the shock, and sensitivities were calculated for each scalar QoI based on both measures of sensitivity. Profiles of sensitivity vs. location downstream of the shock were then integrated to determine an overall sensitivity for each reaction. A weighting function was used in the integration in order to emphasize sensitivities in the region of greatest thermal and chemical non-equilibrium. Both sensitivity analysis methods agree on the six reactions which most strongly affect the density of NO. These six reactions are the N2 dissociation reaction N2+N⇄3N, the O2 dissociation reaction O2+O⇄3O, the NO dissociation reactions NO+N⇄2N+O and NO+O⇄N+2O, and the exchange reactions N2+O⇄NO+N and NO+O⇄O2+N. This analysis lays the groundwork for the application of Bayesian statistical methods for the calibration of parameters relevant to modeling a hypersonic shock layer with the DSMC method.

Metrology of non-thermal capacitively coupled N2–Ar mixture plasma

The effect of argon gas mixing on electron temperature, active species concentration and degree of nitrogen dissociation in a 13.56MHz radio frequency (RF) sustained low pressure Ar–N2 mixture plasma is investigated by using optical emission spectroscopy (OES). The electron temperature is determined from Ar–I emission line intensities by using the modified Boltzmann plot method. It is observed that it decreases with increase in Ar percentage and filling gas pressure in the mixture whereas it increases with the increase in RF power and gas flow rate. The concentration of active species N2(C3Πu) and N2+(B2Σu+) is monitored in terms of the emission intensities of (0–0) band-head of the second positive system (337.1nm) and first negative system (391.4nm) of nitrogen respectively. It is found that the concentration of N2(C3Πu) active species increases with argon mixing up to 60%, while the concentration of N2+(B2Σu+) decreases. The N2 dissociation is found to be enhanced appreciably by argon mixing above 60%. It also increases with RF power and show a peak value at 0.5mbar whereas dissociation fraction is found to be decreased with increasing flow rate.