Vibrational Excitation of N2(B,C) and N+2(B) States in N2 and N2 – H2 Flowing Microwave Discharges

The ro‐vibrational spectra of N₂ microwave discharges have been analysed by emission spectroscopy. It is deduced the rotational and vibrational temperatures of N₂ states. The characteristic of vibrational temperature Θ₁ of the N₂ (X, v) ground state has been specifically determined.It has been found that the N₂ (C, B, v') and N⁺₂ (B, v') radiative states are directly excited by electron collisions on the N₂ (X,v) ground state at a N₂ gas pressure of 0.1 Torr (discharge tube of 5 mm I.D, microwave power 100 Watt) with a Θ₁ value near 10⁴ K. At higher gas pressure up to 5 Torr, the N₂ (C, v') states remain alone to be mainly excited by electron collisions on N₂ (X, v). It is considered the excitations of the N₂ (B, v') states by collisions of electrons and N₂ (X,v > 4) vibrational molecules on the N₂ (A) metastable states.With x < 9% H₂ into N₂, it is observed an increase of N₂, 2^nd pos intensity, resulting of an increase of high energy electrons. Inversely, the N₂, 1^st pos intensity decreased, partly following the decrease of low energy electrons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature time dependence in nitrogen pulse excited microwave discharge

A detailed analysis of the population of the N₂ vibrational states for the N₂ (C ³ II _u,X ¹ _g ⁺ ) electronic states has been carried out. Quantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non-isothermic pulsed discharges in flowing nitrogen at pressures (60–2700) Pa. From the time dependent peak intensities of the second positive system of N₂, the temperature of neutral gas during the h.f. pulses has been determined.     

N2第二正带系发射光谱的理论计算及实验研究

本文利用分子光谱理论系统的计算和分析N₂第二正带系(C³∏_u→B³∏_g)的发射光谱, 以研究光谱强度的分布规律与不同温度条件和气体条件的关系. 基于N₂的三重态能级结构特性, 重点计算和讨论了发射光谱的概个重要参数: 通过求解高、低电子态的哈密顿矩阵得到了振转能级特性; 利用r质心近似法求取了能级间跃迁的电偶极矩函数和爱因斯坦跃迁概率; 进而计算了不同振动和转动温度条件下谱线的强度分布. 进行了N₂和Ar的混合放电实验, 利用实验光谱数据同理论结果进行拟合分析, 确定了N₂分子的振动温度和转动温度分别约为4300 K和800 K. 另外由于潘宁离化效应, N₂浓度减小时谱线强度呈现先增强后减弱的趋势. 实验结果很好的验证了N₂第二正带系光谱理论计算的正确性.     

Collisional transfer of rotational energy in the 2B1 electronic state of nitrogen dioxide

Collisional satellite lines have been observed in fluorescence from nitrogen dioxide excited by the 4545-Å line of the argon laser. The 13_0,13 level of the (0, 8, 0) vibrational state is populated by the laser and undergoes collisionally induced transitions to the 11_0,11, 15_0,15, and 17_0,17 states. These collisionally populated states are identified by their fluorescence to the well-studied (0, 0, 0) and (0, 1, 0) levels of the ground electronic state. These satellite lines are also observed in fluorescence to the (0, 2, 0) and (0, 3, 0) vibrational levels of the ground electronic state. The wavenumbers of those lines, together with those from unrelaxed fluorescence and previously published microwave transitions, allow vibrational and rotational constants for the higher vibrational states to be determined more accurately than was previously possible. Several much weaker forbidden transitions have also been observed, including ΔK_a = 0 through ?6 transitions in the (0, 8, 0)-(0, 0, 1) band.     

Microwave-optical double resonance in NO2

A series of experiments performed to establish the nature of the previously reported microwave optical double resonance signals in electronically excited nitrogen dioxide are reported. The DC stark effect, hyperfine spectrum, and microwave saturation behavior of the double resonance signals observed by exciting NO₂ with the 4880 Å line of an argon ion laser have been studied. The data presented support the assignment of this double resonance signal as occurring within the rovibronic manifold of the ²B₂ electronic state. The observation of a number of new excited state microwave transitions is also reported.     

Optimal laser pulse design for transferring the coherent nuclear wave packet of H+2

Within the Franck–Condon approximation, the single ionisation of H₂ leaves H⁺₂ in a coherent superposition of 19 nuclear vibrational states. We numerically design an optimal laser pulse train to transfer such a coherent nuclear wave packet to the ground vibrational state of H⁺₂. Frequency analysis of the designed optimal pulse reveals that the transfer principle is mainly an anti-Stokes transition, i.e. the H⁺₂ in 1sσ_g with excited nuclear vibrational states is first pumped to 2pσ_g state by the pulse at an appropriate time, and then dumped back to 1sσ_g with lower excited or ground vibrational states. The simulation results show that the population of the ground state after the transfer is more than 91%. To the best of our knowledge, this is the highest transition probability when the driving laser field is dozens of femtoseconds.     

NO excitation and thermal non-equilibrium within a flat plate boundary layer in an air plasma

Optical emission spectroscopy experiments are carried out by recording the radiation from the γ transitions of nitrogen monoxide in an air inductively coupled plasma in interaction with a water-cooled metallic flat plate at moderate pressure. The calibrated results allow to derive the vibrational and rotational temperatures of the NO(A ² Σ ⁺) excited state as well as its densities in the free jet and within the boundary layer by comparison with calculated spectra. Those results are compared with previous ones concerning temperatures and densities of the ground states of the majority species (N₂, O₂ and NO) that were obtained by laser techniques. As for the NO(X ² Π) ground state, vibration and rotation of the excited state are found out of equilibrium. The NO(A ² Σ ⁺) excited state is found to be populated by an energy transfer from the metastable N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}). The steady state of the plasma allows using this property to derive N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}) densities and N₂ electronic excitation temperatures. Close to the wall, a production of excited NO by a catalytic process is also considered involving N₂( A³\varSigma ⁺_uA^{3}\varSigma ^{+}_{u}) as source of adsorbed atoms. The present results confirm that the kinetic temperature cannot be compared to the rotational temperature derived from optical emission spectroscopy in such plasma conditions.     

Vibronic spectra of matrix-isolated lead sulfide

Vibronic spectra are reported for lead sulfide in argon, krypton and SF₆ matrices at low temperatures. Emission stimulated by laser line irradiation of PbS is observed from the v′ = 0 level of three electronic states lying at about 14 500, 18 500 and 21 500 cm^?1 above the ground state. Emission is also observed from an excited state of Pb₂S₂ at about 17 000 cm^?1. In addition, the laser radiation gives rise to the vibrational Raman spectrum of PbS in argon at 423.2 cm^?1 and to a very weak Raman band at 297 ± 2 cm^?1 which we attribute to Pb₂S₂.The effects of temperature on the matrix spectra, of matrix material on the band origins, and of matrix concentration on the vibrational relaxation process, and the apparent degrees of coupling among the electronic states have all been examined. The electronic absorption spectrum of PbS in Ar is reported and the matrix data are compared with available information on gaseous PbS.     

Environmental perturbations on foreign atoms and molecules in solid argon,krypton and xenon

Perturbations which are responsible for the shifts of electronic and vibrational spectra of species trapped in a solid are considered in terms of the intermolecular potential which describes interactions between these species and neighbouring atoms. It is shown that in certain instances London's theory can give an adequate approximation to the dispersion energy between an electronically excited species and a rare gas atom. The experimental shifts in the electronic absorption spectra of Hg, NH and C₂ at lattice sites in rare gas crystals at 4·2°k are explained quantitatively on the basis of a Lennard-Jones (6-12) or (6-8-12) potential between the trapped species and the rare gas atoms. The theory does not adequately explain the shifts in those cases where strong angular dependent forces differing appreciably in the two electronic states are present, data on trapped NH₂ free radicals being presented as a case in point. The interaction of sodium atoms with argon at 4·2°k is very complex, the data being consistent with multiple trapping sites for the atoms, a large repulsive interaction between the excited state of sodium and the rare gas, and apparent removal of the three-fold orbital degeneracy in the excited state by the environmental perturbation. The three-fold orbital degeneracy in the ³P₁ state of mercury was found also to be removed. The blue shift of 1281 cm^-1 for the ³P₁ ← ¹S₀ transition of mercury in solid argon at 4·2°k corresponds almost exactly with the position of one of the two prominent features in the spectrum of mercury in argon gas at comparable densities and illustrates the similarity of structure in the two physical states. The interesting perturbations on the vibrational states of NH and C₂ suggest a close similarity to the effect which causes environmental variations of coupling constants for hyperfine interactions in trapped hydrogen atoms.     

Nitrogen related excitation processes in a mercury bromide laser discharge

The role of nitrogen as a buffer gas constituent in an avalance discharge mercury bromide laser has been examined, and it is shown that a change over in excitation from electron impact dissociation of HgBr₂ to energy transfer dissociation by excited nitrogen occurs at 1.5%N ₂. This is explanable in terms of excitation cross-sections if considerable pumping occurs from excited states of nitrogen which are higher in energy than the metastableA state. When excitation via nitrogen is dominant, a high dischargeE/N value is needed to avoid coupling of energy to unwanted vibrational excitation.     

Analytical potential energy functions for the ground and some excited states of N2

The analytical potential energy functions have been calculated for the ground state X¹Σ⁺_g and four excited electronic states a¹Π_g, A³Σ⁺_u, B′³Σ^?_u and B³Π_g of N₂ molecule using the algebraic and energy-consistent methods (AM-ECM). Based on our previously published full AM vibrational energies and spectroscopic constants, the low-lying force constants f_n, the expansion coefficients a_n and the variational parameters λ in the AM–ECM potentials are determined for these states. The computed AM–ECM potential energy curve of each state is in excellent agreement with the experimental data and better than other analytical potentials.     

N2(B3IIg) Quenching by Ethanol

The reaction rate values for the molecular nitrogen B³II_g state quenching by ethanol for vibrational quantum numbers v′ = 4–12 have been evaluated from the change of N₂ first positive system spectrum at ethanol addition to a high speed, microwave produced, plasma flow. The wall influence is avoided using a 0.9 m large reaction chamber. Computed N₂(B³II_g) quenching rate values are comprised between 0.9 × 10^?10 and 1.4 × 10^?10 cm³ · s^?1, being smaller than the corresponding gaskinetics rate.     

Spectroscopic study of an rf discharge in nitrogen

The absolute populations of the vibrational levels of the B³Πg and C³Π_u states in an rf nitrogen discharge are calculated from the quantum yields of the 1⁺ and 2⁺ systems in the discharge, and the “excitation temperature” of these states is measured. Emission spectroscopic methods are used to determine the vibrational and rotational temperatures of the C³Π_u state, as well as the vibrational temperature of the B³Π_g state. These data are used to estimate the vibrational temperature of the X′∑ _g ⁺ state and the stored energy in the activated nitrogen, and to examine the mechanism by which translational-vibrational degrees of freedom are excited in nitrogen molecules in the discharge.     

Excitation and quenching of ultraviolet nitrogen bands in the mixture of N2 and O2 molecules

Total quenching rate coefficients of three singlet and three triplet states of molecular nitrogen in the collisions with O₂ molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of N₂^? molecules are compared with the available experimental data. An influence of collisional processes on vibrational populations of electronically excited N₂(a¹Π_g) and N₂(A³Σ_u⁺) molecules is studied for conditions of laboratory discharge in N₂ and O₂ at admixtures of molecular oxygen 0%-20% for the pressures 1-1000 Pa. It is indicated that molecular collisions cause changes in relative populations of vibrational levels of these states and intensity relations of ultraviolet bands of N₂ with rise in the pressure and the O₂ admixture.     

Vibrationally unrelaxed fluorescence in matrix isolated CF2

The CF₂ emission spectrum in rare gas solids involves both the symmetric vibrations, ν₂ (668 cm^?1) and ν₁ (1120 cm^?1). A vibrationally unrelaxed emission is observed following selective excitation of the higher vibrational levels in the ν₂ manifold, and we measure vibrational relaxation rates of 2 × 10⁸/sec and 1.1 × 10⁸/sec, respectively, for the 2-1 and 1-0 relaxation in argon. All the vibrational bands show a strong coupling to the lattice modes, with a weak ZPL and strong phonon wing. This results from the change in geometry between the ground and excited electronic states.     

Optical study of radicals (OH,O, H,N) in a needle-plate bi-directional pulsed corona discharge

In this study, analysis of optical emission spectra are used for the detection of OH (A²Σ) radicals and O (3p⁵P), H_α (3P) and N (3p⁴P) active atoms produced by the high-voltage bi-directional pulsed corona discharge of N₂ and H₂O mixture gas in a needle-plate reactor at one atmosphere. The relative vibrational populations and the vibrational temperature of N₂ (C, v') are determined. The effects of pulse peak voltage, pulse repetition rate and the added O₂ flow rate on the relative populations of OH (A²Σ) radicals and O (3p⁵P), H_α (3P) and N (3p⁴P) active atoms are investigated. It is found that when pulse peak voltage and pulse repetition rate are increased, the relative populations of those excited states radicals rise correspondingly. The relative population of OH (A²Σ) radicals decreases with increasing the flow rate of oxygen. The relative populations of O (3p⁵P), H_α (3P) and N (3p⁴P) active atoms increase with the flow rate of oxygen at first and exhibit a maximum value at about 30 ml/min. When the flow rate of oxygen is increased further, the relative populations of those excited states active atoms decrease correspondingly. The main involved physicochemical processes also have been discussed.     

Matrix isolation infrared observation of N3 using a nitrogen microwave discharge plasma source

The asymmetric stretching band of the N₃ radical in a nitrogen matrix at 1657.5?cm^?1 has been observed by directing the output of a nitrogen microwave discharge plasma source onto a CsI window at 12?K. The identification and assignment of this band to the N₃ radical has been accomplished by performing isotopic experiments, matrix annealing experiments, and photolysis experiments. The observed N₃ band positions are compared to literature frequencies observed in matrix isolation experiments using other generation sources and to literature theoretical frequencies calculated using high level ab initio and density functional theory methods. Temperature-dependent deposition experiments (10–20?K) and additional isotopic discharge plus co-deposition experiments are also performed in an effort to determine if the N₃ radical is being formed in the gas phase or by matrix surface reactions, and in order to gain insight into the reaction mechanism. After considering all of the mechanistic evidence (temperature-dependent and isotopic discharge/co-deposition spectra, theoretical reaction energetics, gas phase reaction kinetics, isotopic N₃ distributions), it is concluded that the N₃ radicals are being formed from the reaction of N(²D) atoms with vibrationally excited N₂ molecules in the nitrogen matrix via a linear (end-on) pathway.     

Chemiluminescent GeCl4 + O2 + Ar/He/Reactions

A chemiluminescent flame was produced in the reaction between GeCl₄ and an excited mixture of argon or helium with oxygen. Spectra of the reaction products were recorded and studied. Relative populations of the products in analyzed electronic, vibrational and rotational states corresponded to different temperatures.     

Electron resonance studies of the renner effect

The gas phase electron resonance spectra of NCO in its ground ²Π_3/2 vibronic state and in two excited vibronic states are described. Theoretical analysis of the spectra yields effective g values for the three states. In additon the ¹⁴N magnetic hyperfine and electric quadrupole coupling constants and the electric dipole moment are determined. The theory of the Renner coupling of electronic and vibrational motion is extended, and shown to account for anomalous contributions to the g values. The theory also shows that these contributions are closely related to the Renner coupling constant.     

Determination of the population of the A 3Σu electronic state of nitrogen molecules in a glow-discharge plasma

Results on determining the population of the A ³Σ_u electronic state of N₂ molecules in a gas discharge using a relatively simple spectroscopic technique are reported. The technique proposed can be used not only in pure N₂, but also in nitrogen-containing gas mixtures. The populations of the metastable and nonequilibrium B ³Π_g states of nitrogen molecules are determined. It is shown that the electron-impact excitation is a dominant mechanism for populating the B ³Π_g state.