Excitation Of N2 Research Articles

Spatial distribution population of excited He, Ne and N2 levels in a pulsed microwave plasma generated by a surface wave

Spectroscopic and electronic diagnostics are applied to determine the temporal and spatial evolution of excited species created in He or Ne-N2 plasmas produced by a microwave surfaguide at a pressure of a few Torr. The excited-states population has a maximum near the wall. Electron density is maximum on the axis (1013 cm-3 at 10 Torr). Its radial distribution is well fitted by a Bessel J0(r) function. As a consequence the metastable population is also maximum along the axis.

Theoretical and experimental investigation of electron-beam-controlled synthesis of nitrogen-containing compounds

A theoretical and experimental investigation is made of the electron-beam-controlled method of synthesizing nitrogen-containing compounds. It is shown that the basic chemically active form of nitrogen in the electron-beam-controlled discharge are the vibrationally excited molecules N2. The experimental procedure and the results are meported on the synthesis of nitrogen oxides, hydrogen cyanide, and phosphorus nitride. The isotopic compositions of the vibrationally excited nitrogen and carbon monoxide are calculated.

Photodissociation of ClN3 at 193 and 249 nm

Experiments directed toward elucidating the nature of fragments produced by the photodissociation of ClN3 have been performed. The utlraviolet absorption spectrum of this molecule exhibits three features between 300 and 170 nm, with λmax = 250, 205, and <170 nm. The shortest wavelength feature (whose maximum was not resolved) was the strongest of the three, with ε170 = 5000 ℓ mol−1 cm−1. Photolysis of ClN3 at 193 nm produces N2 and NCl fragments in both the singlet and triplet manifolds. In the singlet manifold of fragments, emission from electronically excited NCl(b 1Σ+) was observed. The NCl(b 1Σ+) molecules are also vibrationally excited, and emission from levels as high as v′ = 10 was recorded. Time resolution of the NCl(b 1Σ+) emission indicated that the higher vibrational levels were quenched by the gas mixture (∼3% ClN3 in helium) much more rapidly than the lower vibrational levels. The rate constant for quenching of the low v′ levels (v′ = 0–2) of NCl(b 1Σ+) was determined to be kQ = (1.72±0.05)×103 s−1 Torr−1; the rate constant for quenching of the higher levels (v′?8) was found to be kQ = (3.8±0.2)×104 s−1 Torr−1. The spontaneous emission rate for NCl(b 1Σ+), v′ = 0–2, was measured to be A = 1590±160 s−1. In the triplet manifold of fragments, photolysis at 193 nm produces excited N2(A 3Σ+u) metastable molecules. The presence of this species was determined from the observation of N2(C 3Πu)→(B 3Πg) emission produced by energy pooling processes, and from the excitation of NO by energy transfer from the N2 metastables. Photolysis of ClN3 produces at 193 nm excited singlet and triplet fragments with comparable probability. Photolysis at 249 nm also generates both excited singlet and triplet NCl and N2 fragments. Emission from vibrationally excited NCl(b 1Σ+) was again observed, and the initial vibrational distribution appeared to be similar to that found for photolysis at 193 nm. The yields for production of NCl(b 1Σ+) at 193 and 249 nm are approximately equal. Photolysis at 249 nm also produces N2(A 3Σ+u) fragments, although in substantially smaller yield than found at 193 nm.

Resolution of angular rotational rainbows in Na 2 + Ne, Ar collisions

State-to-state dfferential cross sections for rotational excitation in Na 2-Ne collisions have been measured and the characteristics of such processes involving repulsive surfaces demonstrated. The rotational rainbow maxima shift to larger scattering angles and broaden as the angular momentum transfer increases. Good agreement with IOS calculations is found. Results for Na 2-Ar are included.

Vibrational excitation of ozone and molecular fluorine reactions in cryogenic matrices

Attempts have been made to induce under cryogenic conditions reactions between O3 and C2H2, C2H4, NO2, and NO, and between F2 and C2H4, by selective vibrational excitation of nearest neighbor reactant pairs. Samples in inert gas or nitrogen matrices at 12 K were irradiated with grating-tuned cw CO2 and CO lasers. Only linewidth narrowing due to thermal effects was observed in the first three systems with laser excitation of ν3 of ozone, ν7 and ν7+ν8 of ethylene, or ν3 of NO2. However, the dark reaction NO+O3→NO2+O2 in nitrogen matrices could be significantly enhanced by exciting the NO stretch of NO⋅O3 pairs at 1874 cm−1. No products were detected upon prolonged excitation of ν7 of C2H4⋅F2 reactive pairs at 953 cm−1 whereas excitation of ν7+ν8 of ethylene at 1896 cm−1 did promote reaction with an approximate quantum yield of 10−4. The products are trans- and gauche-1,2-difluorethane, vinyl fluoride, and HF. Kinetic studies revealed first order kinetics with linear dependence of the rate constant on laser intensity, which indicates a single photon photochemical process. The observed products are consistent with a molecular four center reaction mechanism, rather than the gas phase free radical mechanism. Isolated C2H4⋅F2 pairs produce predominantly the elimination products vinyl fluoride and HF, whereas an additional ethylene molecule in the reaction cage increases 100-fold the stabilization of the reaction adduct CH2F–CH2F°. The gauche/trans ratio of 1,2-difluorethane is near 2, close to the high temperature limit.

Transfer and storage of vibrational energy in liquids: Liquid nitrogen and its solutions with carbon monoxide

We have produced vibrational excitation in liquid nitrogen and its solutions with carbon monoxide by flooding the samples with infrared radiation from a blackbody source. Infrared fluorescence from these excited liquids was monitored in order to investigate their relaxation kinetics and spectral profiles. For the first time the collision induced emission of excited liquid nitrogen is reported. The radiative decay of undoped nitrogen, which is a measure of the ability of the liquid to store vibrational energy, was measured to be 45±5 sec; however, fluorescence could be detected for over 2 min. New relaxation channels are opened for excited N2 when CO is added and the lifetimes are shorter. These relaxation channels were investigated in detail. The radiative lifetime of excited CO in liquid nitrogen was determined. We were also able to place upper limits on the V–T,R relaxation rates of excited CO and N2 in the liquid. In addition to these rate constants, a model for radiation trapping was developed which successfully mimicked the observed kinetic and spectral behavior of the liquid N2–CO system in the region where self-absorption dominates.

Vibrational relaxation of acetylene and acetylene–rare-gas mixtures

Vibrational relaxation of acetylene (C2H2) and acetylene–rare-gas mixtures has been investigated using laser-induced fluorescence. Time-dependent fluorescence signals from the vibrational modes ν2 and ν5 have been recorded, following excitation of ν3 and (ν2+ν4+ν5) at 3300 cm−1 with pulses of a tunable optical parametric oscillator. The activation rate of ν2 and ν5 were estimated to be ≳880 ms−1 Torr−1 and ≳330 ms−1 Torr−1, respectively. The following V-T/R relaxation rates have been obtained from the decay of the ν5 fluorescence signal: (12.7±1.1) ms−1 Torr−1 for C2H2 as collision partner, (0.46±0.05) ms−1 Torr−1 for Ne, (0.66±0.06) ms−1 Torr−1 for Ar, (0.67±0.04) ms−1 Torr−1 for Kr, and (0.57±0.04) ms−1 Torr−1 for Xe. Surprisingly small V–V deactivation rates of the CC stretching vibration ν2 have been measured. These are (21.3±1.0) ms−1 Torr−1 for C2H2 collisions, (0.63±0.06) ms−1 Torr−1 for Ne, (0.78±0.08) ms−1 Torr−1 for Ar, (0.93±0.09) ms−1 Torr−1 for Kr, and (0.77±0.09) ms−1 Torr−1 for Xe. Acetylene relaxation mechanisms compatible with these rates are considered.

Temperature dependence of electronic to vibrational energy transfer from Br(42P1/2) to 12CO2 and 13CO2

Temperature dependent quenching cross sections for the collisional deactivation of Br(42P1/2) by 12CO2 and 13CO2 were determined by monitoring the time resolved molecular fluorescence from the ν3 vibrational mode of CO2. These cross sections decrease with increasing temperature in the range 296–600 °K, indicating that near resonant channels dominate the quenching processes in both molecules. The room temperature rate coefficients for the quenching of Br* by 12CO2 and 13CO2 are (5.0±0.2)105 and (2.3±0.1)105 sec−1 torr−1, respectively, with about half of the quenching collisions resulting in excitation of the ν3 mode in the case of each molecule. By monitoring the amplitudes of the ν3 fluorescence signals from 13CO2 at different temperatures, the temperature dependence of the electronic to vibrational (E→V) energy transfer cross sections into states containing ν3 excitation was obtained. The experimental results are compared with calculations of E→V energy transfer cross sections which are based on long-range multipolar interactions.

Photo-induced vibrational predissociation of the van der Waals molecule (N2O)2

An apparatus is described in which a supersonic beam of nitrous oxide in helium impinges upon a 2 °K silicon bolometer, or alternatively, is detected by a mass spectrometer. Laser excitation of the beam in the vicinity of ν3 of nitrous oxide decreases the flux of the van der Waal’s molecule (N2O)2 reaching the bolometer. Thus, excitation of ν3 is followed by vibrational predissociation of the van der Waal’s bond.

Measurement and evaluation of differential scattering cross sections for Na2P3/2with Hg

The differential cross section has been measured for the interaction of Na 2P3/2 with Hg. The excitation of Na has been achieved with linearly polarised light of a CW dye laser. The measurements have been evaluated by fitting the parameters of a pseudopotential from which the interatomic potentials have been obtained. The scattering calculation for these interatomic potentials is performed by integrating the coupled Schrodinger equations for the six coupled channels resulting from the P states with J=3/2 and 1/2 and their respective values of mj. This experiment and the experiment for the ground-state interaction are now both described by a common calculation using the pseudopotential method.

Vibrational energy transfer in methane and methane–rare-gas mixtures

The vibrational relaxation time for the asymmetric stretch ν3 of CH4 is 3.9±0.6 μsec torr in pure CH4 and 12, 13, 10, 5.9, 5.5, 5.0, 11, and 9.5 μsec torr (±20%) for CH4 dilute in 3He, 4He, Ne, Ar, Kr, Xe, H2, and HD, respectively, at 295°K. The ν3 fundamental was pumped by a tunable infrared laser. The rise time for bending fluorescence following ν3 excitation is 30%–50% shorter than the ν3 decay. In pure CH4, measurements of emission from 2ν4 and ν2+ν4 indicate that a large fraction of the vibrational energy is channeled through these two levels. The main relaxation path appears to be transfer from ν3 through 2ν4 to ν4, with the ν2 bending vibration being excited mostly in the later stages of V→V transfer.

Differential K-shell excitation in slow Na+-Ne encounters

The differential K X-ray production probability in 420 keV Na+-Ne collisions as obtained from a coincidence experiment is compared with the results of a Ne+-Ne experiment. A possible mechanism for the observed K-shell excitation in Na+-Ne collisions is suggested.

Thermal energy charge transfer of Ne+ with vibrational excited N2

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Excitation of Na D-Line Radiation in Collisions of Sodium Atoms with Internally Excited H2, D2, and N2

Excitation of D-line radiation in collisions of Na atoms with vibrationally excited N2, H2, and D2 has been studied in two modulated crossed beam experiments. In both experiments, the vibrational excitation of the molecules was provided by heating the molecular beam source to temperatures in the range of 2000–3000°K, which was assumed to give populations according to the Boltzmann expression. In the first experiment, a total rate coefficient was measured as a function of molecular beam temperature, with absolute calibration of the photon detector being made using the black body radiation from the heated molecular beam source. Since heating affects both the internal energy and the collisional kinetic energy, the first experiment could not determine the relative contributions of internal energy transfer vs collisional excitation. The second experiment achieved partial separation of internal vs kinetic energy transfer effects by using a velocity-selected molecular beam. Using two simple models for the kinetic energy dependence of the transfer cross section for a given change in vibrational quantum number, the data from both experiments were used to determine parameters in the models. Evidently the most probable situation is that most of the Na excitation energy comes from internal vibrational energy, with the remainder coming from kinetic energy. The paper discusses the consequences of the detailed results with respect to the excitation of sodium radiation in aurorae.

The Reaction of Active Nitrogen with Carbonyl Chloride

The reaction between active nitrogen and COCl2 in an unheated reaction vessel has been studied over a large range of initial reactant conditions. Analytical studies have shown CO and Cl2 to be the only reaction products, effectively produced in equal amounts. The maximum extent of reaction corresponded to no more than 10% of the available N atoms. The reaction was found to change from first order in both N and COCl2 for [COCl2]0/[N]0 < ~0.1, to zero order in COCl2 and second order in N, with [COCl2]0/[N]0 > ~0.3. The reaction appears to be initiated by energy transfer from an excited N2 species.

Reactions between N2+ and N2

Apparent cross sections for the reactions N2++N2→N++N+N2, N2++N2→N3++N, have been measured for laboratory kinetic energies E of N2+ between 1 and 45 eV. The primary ions are produced by electron bombardment and mass analyzed prior to reaction. The bombarding electron energy is varied from 19 to 90 eV, and the effects of excited, long-lived states of N2+ on the reactions are studied. Both reactions proceed when N2+ is in long-lived excited states and when N2+ is in the X 2Σg+ and/or A 2Πu states. When E≲15 eV, Reaction (1) proceeds primarily from long-lived states of N2+ about 8.5±1.5 eV above the ground state. There may be several long-lived excited N2+ states involved in the production of N+ and N3+ at low E, and some or all of these states may be involved in long-lived emissions which have been previously observed. A survey of the available information on N2+ suggests that detailed comparisons with theory will be seriously hampered by uncertainties in the production and lifetimes of the various states of N2+.

Excitation of Sodium Atoms by Collisions with Vibrationally Excited Molecules behind Shock Waves

Abstract Simultaneous measurements of Na D and CO fundamental emissions have been made behind a shock wave in CO–Ar or CO–N2–Ar mixture containing a trace of Na vapor. The relaxation of a population in each vibrational level is calculated by use of Montroll-Shuler equation. The Na D emission intensity behind the shock wave in the 1.5% CO+Ar mixture nearly follows the relaxation of CO molecules excited to a vibrational level v=3 or 4, which is energetically lower than the 32P state of Na. This means that most Na atoms are excited by collisions with CO molecules in a level higher than v=3, and that the Na D reversal temperature exceeds the vibrational temperature of CO molecules behind the shock wave. In contrast to this, excitation of Na behind the shock wave in the 1.7% CO+49.3% N2+49.0% Ar mixture is due to collisions with N2 molecules in a level higher than v=6, and a nearly resonant vibrational-to-electronic energy transfer is realized. The relative values of the exciting rate kve by collisions with CO or N2 in a level v are determined to be k1e :k2e :k3e k4e :k5e=<0.01 : 0.04: 1 : 1.6 : <2 for Na–CO and k4e :k5e :k6e :k7e :k8e=<0.03 : 0.21 : 1 : 1.4 : <2 for Na–N2 collisions at about 2600°K.

Mechanism of a CO–N2 laser. II. Study by electronic spectroscopy

The study of the CO–N2 laser described in a preceding paper is pursued here by electronic spectroscopy. It is shown that the emission intensity of the red and violet systems of the CN radical present in the laser tube is related to the infrared laser action. Investigation of this effect leads to the conclusion that, after its formation, CN is electronically excited by collision, with vibrationally excited nitrogen molecules. The effect on the laser and CN emissions of a small addition of gases such as O2, NO, and CO2 is studied and discussed. All the observed facts are interpreted by a theory based only on the presence of N(4S) atoms and vibrationally excited molecules N2(X1Σg+).

Excitation of sodium in certain reactions behind shock waves

1. In the early stages of the hydrogen-oxygen reaction (less than 10% H2 depletion) the electronic excitation of Na atoms and OH radicals and the vibrational excitation of OH and H2O exceed the equilibrium values. 2. A comparison of the efficiency of the various sources of sodium excitation in the induction period of the H2−O2 reaction shows that the sodium is excited in collisions with OH and H2O possessing a nonequilibrium reserve of vibrational energy. 3. The nature of Na excitation in the systems C2H2−O2 and H2−O2 is practically the same; the excitation of Na in CH4−O2 and H2−Cl2 mixtures is equilibrium in character.

Trapping and quenching of potassium resonance radiation

The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.