Population Of Vibrational Levels Research Articles

Effect of molecular diameters on state-to-state transport properties: The shear viscosity coefficient

Shear viscosity coefficient is calculated for both equilibrium and strongly non-equilibrium state-to-state vibrational distributions taking into account increasing diameters of vibrationally excited molecules. Under conditions of local thermal equilibrium, the effect of vibrational excitation on the shear viscosity coefficient is found to be negligible for temperatures below 5000K. For T>10000K, the contribution of excited states becomes important. Under non-equilibrium conditions characteristic for shock heated and supersonic expanding flows vibrational level populations deviate strongly from the Boltzmann distribution. Nevertheless, estimated coupled effect of molecular size and non-Boltzmann distributions on the shear viscosity coefficient is negligible.

Effect of Blue Jets on Atmospheric Composition: Feasibility of Measurement From a Stratospheric Balloon

The feasibility study of the HALESIS (High-Altitude Luminous Events Studied by Infrared Spectro-imagery) project is presented. The purpose of this experiment is to measure the atmospheric perturbation in the minutes following the occurrence of transient luminous events (TLEs) from a stratospheric balloon in the altitude range of 20-40 km. The instrumentation will include a spectro-imager embedded in a pointing gondola. Infrared signatures of a single blue jet were simulated under the assumption of local thermodynamic equilibrium (LTE), and were then compared with a panel of commercially available instrument specifications. The sensitivity of the signatures with a local perturbation of the main vibrational energy level populations of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CO, NO, O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O was measured and the infrared signatures of a single blue jet taking into account non-LTE hypotheses were compared with the same panel of commercially available instrument specifications. Lastly, the feasibility of the study is discussed.

Numerical simulation of the two-dimensional structure of glow discharge in molecular nitrogen in light of vibrational kinetics

A two-dimensional computer model of glow discharge in molecular nitrogen in axisymmetric geometry is presented. The glow discharge structure is described within the diffusion-drift model, while the kinetic parameters of the model used are calculated from the solution to the kinetic Boltzmann equation. Calculations of the energy accumulated on the electronically and vibrationally excited levels of molecules and the effectiveness of electron energy conversion to the Joule heat are performed. In the context of state-to-state kinetics of anharmonic oscillators, populations of vibrational levels of molecular nitrogen are calculated.

Experimental determination of the rate of V-V collisional relaxation in (14)N2 in its ground (X(1)Σ(g)(+)) electronic state between 77 and 300 K.

We propose new values for the V-V collisional energy transfer rate constant of (14)N2 (X(1)Σg(+)) at different temperatures in collisions between molecules in the v = 1 and v = 0 vibrational states. The values were obtained experimentally by means of a time-resolved double resonance pump-probe stimulated Raman setup in which the stimulated Raman technique was used for both the pump and the probe stage. The main feature of the experiment is the fact that population pumping is done with rotational (and thus spin) selectivity, that is, only molecules belonging to the ortho spin variety of (14)N2 are promoted to v = 1. The probe stage is then used to monitor the decay of this ortho rotational population placed in v = 1 and the emergence of a para population in that same vibrational level. Since the only possible mechanism for the arrival of para population to v = 1 is collisional V-V energy transfer, the evolution of the ortho/para ratio in v = 1 is used to quantify the rate constant of the process. The measurements were conducted at 77, 136, 226 and 300 K. The 300 K value had been measured and calculated before by other authors, but a spread larger than an order of magnitude existed between their results. Our proposed value is more precise than previous ones and lies near the mid-point of that interval. The low-temperature values of the rate constant are reported here for the first time. The availability of data at several temperatures has allowed us to unequivocally determine the existence of a strong negative temperature dependence of the rate constant between 77 and 300 K that exhibits a linear behavior in a Landau-Teller plot in this temperature interval.

Effect of updated relaxation rate constants on the H 2 O vibrational level populations and ro-vibrational spectra in the mesosphere and lower thermosphere

Abstract This paper discusses the formation mechanisms of infrared radiation in H2O ro-vibrational bands in the mesosphere and lower thermosphere (MLT). At these heights and above, the vibrational levels of the molecules involved in radiative transitions are not in local thermodynamic equilibrium (LTE) with the surrounding medium, and the biggest uncertainty source in modeling the IR radiation in molecular bands is associated with the corresponding vibrational kinetics model parameters. In this study, we re-analyze available experimental data of Barnes et al. (2004) and Zittel and Masturzo (1991) and update the rate constant of V–V exchange (k) corresponding to the second vibrational number v2 increase by two and the first (or the third) quantum number decrease by one. The estimated values of k for quenching by N2 and O2 are 1.7 × 10−12 and 1.3 × 10−12 cm3 s−1, respectively. These values are about four times larger than the values used in all earlier models of non-LTE populations of vibrational levels and IR radiation in ro-vibrational bands of H2O. We state that using the same k for all processes of vibrational–vibrational energy exchange does not correspond to laboratory experiments and can lead to offsets both in calculating the vibrational level populations and in H2O concentration retrievals from IR spectral radiance. We provide the estimates of these offsets as well as a list of spectral microwindows, in which H2O radiance is sensitive to uncertainty of k.

O2(b(1)Σ(+)(g), υ = 0, 1) relative yields in O((1)D) + O2 energy transfer.

Energy transfer from O((1)D) to O2 is the main source of O2(b(1)Σ(+)(g) in vibrational levels υ = 0 and 1 in the Earth's thermosphere. Knowledge of the relative yields for O2(b(1)Σ(+)(g) production in υ = 0 and 1 is essential for a reliable interpretation and modeling of the O2 atmospheric band emissions (b(1)Σ(+)(g) - X (3)Σ(-)(g) from these two vibrational levels. We report laboratory measurements of the relative yields at room temperature. In the experiments, O2(b(1)Σ(+)(g), υ = 0, 1) is generated by O((1)D) + O2 collisions following partial photodissociation of O2 at 157.6 nm. O2(b(1)Σ(+)(g), υ = 0, 1) emission detection is used to monitor the temporal evolution of the vibrational level populations. The measured fractional yield for υ = 1 is 0.8 ± 0.1, in contrast with the results of previous studies that indicated dominant O2(b(1)Σ(+)(g), υ = 0) production. A revision is warranted of the values used for these relative yields in atmospheric models.

Nitric oxide kinetics in the afterglow of a diffuse plasma filament

A suite of laser diagnostics is used to study kinetics of vibrational energy transfer and plasma chemical reactions in a nanosecond pulse, diffuse filament electric discharge and afterglow in N2 and dry air at 100 Torr. Laser-induced fluorescence of NO and two-photon absorption laser-induced fluorescence of O and N atoms are used to measure absolute, time-resolved number densities of these species after the discharge pulse, and picosecond coherent anti-Stokes Raman spectroscopy is used to measure time-resolved rotational temperature and ground electronic state N2(v = 0–4) vibrational level populations. The plasma filament diameter, determined from plasma emission and NO planar laser-induced fluorescence images, remains nearly constant after the discharge pulse, over a few hundred microseconds, and does not exhibit expansion on microsecond time scale. Peak temperature in the discharge and the afterglow is low, T ≈ 370 K, in spite of significant vibrational nonequilibrium, with peak N2 vibrational temperature of Tv ≈ 2000 K. Significant vibrational temperature rise in the afterglow is likely caused by the downward N2–N2 vibration–vibration (V–V) energy transfer. Simple kinetic modeling of time-resolved N, O, and NO number densities in the afterglow, on the time scale longer compared to relaxation and quenching time of excited species generated in the plasma, is in good agreement with the data. In nitrogen, the N atom density after the discharge pulse is controlled by three-body recombination and radial diffusion. In air, N, NO and O concentrations are dominated by the reverse Zel'dovich reaction, N + NO → N2 + O, and ozone formation reaction, O + O2 + M → O3 + M, respectively. The effect of vibrationally excited nitrogen molecules and excited N atoms on NO formation kinetics is estimated to be negligible. The results suggest that NO formation in the nanosecond pulse discharge is dominated by reactions of excited electronic states of nitrogen, occurring on microsecond time scale.

Time-dependent approach to spin-vibronic coupling: Implementation and assessment

In this work, we present the generalization of a time-dependent method for the calculation of intersystem crossing (ISC) rates in the Condon approximation. When ISC takes place between electronic states with the same orbital type, i.e., when the transition is forbidden according to the El-Sayed rules, it is necessary to go beyond the Condon approximation. Similar to the Herzberg-Teller expansion of the vibronic interaction, the electronic spin-orbit matrix elements are assumed to depend linearly on the nuclear coordinates. The ISC rate is then a sum of three contributions: a direct, mixed direct-vibronic, and vibronic term. The method, presented in this work, is based on the generating function formalism and the multi-mode harmonic oscillator approximation. In addition to the zero-temperature case, we implemented formulae for finite-temperature conditions assuming a Boltzmann population of vibrational levels in the initial state. Tests have been carried out for a variety of molecules for which literature data were available. We computed vibronic one-photon spectra of free-base porphyrin and free-base chlorin and calculated ISC rates for xanthone, thioxanthone, thionine, as well as free-base porphyrin and found excellent agreement with previous results. Quantitative rates for triplet formation in rhodamine A have been determined theoretically for the first time. We find the S1↝ T2 channel to be the major source of triplet rhodamine formation in the gas phase.

Rovibronic structure in slow photoelectron velocity-map imaging spectroscopy of CH2CN− and CD2CN−

We report high-resolution anion photoelectron spectra of the cryogenically cooled cyanomethide anion, CH2CN(-), and its isotopologue, CD2CN(-), using slow photoelectron velocity-map imaging (SEVI) spectroscopy. Electron affinities of 12 468(2) cm(-1) for CH2CN and 12 402(2) cm(-1) for CD2CN are obtained, demonstrating greater precision than previous experiments. New vibrational structure is resolved for both neutral species, especially activity of the ν5 hydrogen umbrella modes. The ν6 out-of-plane bending mode fundamental frequency is measured for the first time in both systems and found to be 420(10) cm(-1) for CH2CN and 389(8) cm(-1) for CD2CN. Some rotational structure is resolved, allowing for accurate extraction of vibrational frequencies. Temperature-dependent SEVI spectra show marked effects ascribed to controlled population of low-lying anion vibrational levels. We directly measure the inversion splitting between the first two vibrational levels of the anion ν5 umbrella mode in both species, finding a splitting of 130(20) cm(-1) for CH2CN(-) and 81(20) cm(-1) for CD2CN(-). Franck-Condon forbidden activity is observed and attributed to mode-specific vibrational autodetachment from the CH2CN(-) and CD2CN(-) dipole bound excited states. We also refine the binding energy of the anion dipole bound states to 39 and 42 cm(-1), respectively, for CH2CN(-) and CD2CN(-).

Picosecond CARS measurements of nitrogen vibrational loading and rotational/translational temperature in non-equilibrium discharges

Picosecond coherent anti-Stokes Raman spectroscopy (CARS) is used to study vibrational energy loading and relaxation kinetics in nitrogen and air ns pulsed non-equilibrium plasmas, in both plane-to-plane and pin-to-pin geometries. In 10 kHz repetitively pulsed plane-to-plane plasmas, up to ∼50% of coupled discharge power is found to load vibrations, in good agreement with a master equation kinetic model. In the pin-to-pin geometry, ∼40% of total discharge energy in a single pulse in air at 100 Torr is found to couple directly to nitrogen vibrations by electron impact, also in good agreement with model predictions. Post-discharge, the total quanta in vibrational levels v = 0–9 is found to increase by ∼60% in air and by a factor of ∼3 in nitrogen, respectively, a result in direct contrast to modelling results which predict the total number of quanta to be essentially constant until ultimately decaying by V–T relaxation and mass diffusion. More detailed comparison between experiment and model show that the vibrational distribution function (VDF) predicted by the model during, and directly after, the discharge pulse is in good agreement with that determined experimentally. However, for time delays exceeding ∼1 µs, the experimental VDF shows populations of vibrational levels v ⩾ 2 greatly exceeding modelling results, which predict their predominant decay due to net downward V–V transfer and corresponding increase in v = 1 population. This is at variance with the experimental results, which show a significant monotonic increase in the populations of levels v = 2–9 at t ∼ 1–10 µs after the discharge pulse, both in nitrogen and air, before gradually switching to relaxation at t ∼ 10–100 µs. It is concluded that a collisional process is likely feeding high vibrational levels at a rate which is comparable to the rate at which population of the high levels is lost due to net downward V–V energy transfer. A likely candidate for the source of additional vibrational quanta is quenching of metastable electronic states of nitrogen to highly excited vibrational levels of the ground electronic state. The effect of electronic-vibrational (E–V) coupling on time-resolved N2 vibrational populations and temperature, estimated using a phenomenological E–V energy transfer model, provides qualitative interpretation of the present experimental results.

Vibrational kinetics of electronically-excited molecules in nitrogen discharge plasma

A model on formation of the vibrational distribution function of metastable electronically excited states in nitrogen discharge plasma is presented. By means of comparison with the experimental data the rate constants for the reaction have been clarified. It is assumed that the probability of population of states by collisional deactivation of N2(B 3Πg, v′) molecules is proportional to the Franck–Condon factors of correspondent transitions, i.e. that the quenching is essentially vertical. The results of calculations carried out under this assumption are in agreement with measured vibrational distribution at the end of pulsed high current discharge in nitrogen.Study of a variation of the population of vibrational level in the afterglow of streamer discharge in nitrogen at atmospheric pressure has been performed. It is shown that the dynamics of number density depends essentially not only on their loss in the pooling reaction product, but also on additional population due to the quenching of high vibrational levels. The fraction of dissociation channel in the process of deactivation by oxygen molecules have been calculated. It is shown that temporal evolution of the fraction of the dissociation channel is first of all associated with a variation of the relative population of the vibrational level . In air discharge plasma at high pressure, the population of state is relatively low, so the fraction of the dissociation channel in the deactivation of all electronically excited states of nitrogen by oxygen exceeds 90–95%.

Electronic Spectra and Reversible Photoisomerization of Protonated Naphthalenes in Solid Neon

Alpha- and beta-protonated naphthalenes (α- and β-HN(+)) were investigated by electronic absorption and fluorescence spectroscopies in 6 K neon matrixes using a mass-selected C(10)H(9)(+) ion beam. The absorption spectra reveal S(1)/S(2) ← S(0) transitions with onsets at 502.1 and 396.1 nm for α-HN(+), and 534.5 and 322.3 nm in the case of β-HN(+). Wavelength-dispersed fluorescence was detected for α-HN(+), starting at 504.4 nm. Light-induced α-HN(+) → β-HN(+) isomerization was observed upon S(2) ← S(0) excitation of α-HN(+), whereas β-HN(+) relaxed back into the more stable alpha form either upon excitation to S(1) or via thermal population of the ground state vibrational levels near the top of the energy barrier between the two isomers. The intramolecular proton transfer leading to the α-HN(+) ↔ β-HN(+) photoisomerization is fully reversible. The observations are explained with the support of theoretical calculations on the ground- and excited states of the isomers, vertical excitation and adiabatic energies, minimum-energy pathways along the relevant reaction coordinates, and conical intersections between the electronic states.

Three-block model of the kinetics of vibrationally excited I2(X) molecules in the active media of oxygen — iodine lasers

A three-block model of the kinetics of vibrationally excited I2(X) molecules in the active media of chemical oxygen — iodine lasers is developed. Instead of the system of equationsdescribing a change in the concentrations of I2(X, u) (u=0 — 47) molecules, this model uses equations for the total concentrations of iodine molecules belonging to the blocks of vibrational levels with u ≤ 10, u = 11 — 24, and u ≥ 25. Effective deactivation rate constants of I2(X, 11 ≤ u ≤ 24) molecules are found for laser media of different compositions. The results of calculations performed using the proposed model agree with experimental data and are close to the parameters calculated previously by using the total system of equations for populations of individual vibrational levels of I2(X, u).

On the dependence of the OH&amp;lt;sup&amp;gt;*&amp;lt;/sup&amp;gt; Meinel emission altitude on vibrational level: SCIAMACHY observations and model simulations

Abstract. Measurements of the OH Meinel emissions in the terrestrial nightglow are one of the standard ground-based techniques to retrieve upper mesospheric temperatures. It is often assumed that the emission peak altitudes are not strongly dependent on the vibrational level, although this assumption is not based on convincing experimental evidence. In this study we use Envisat/SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) observations in the near-IR spectral range to retrieve vertical volume emission rate profiles of the OH(3-1), OH(6-2) and OH(8-3) Meinel bands in order to investigate whether systematic differences in emission peak altitudes can be observed between the different OH Meinel bands. The results indicate that the emission peak altitudes are different for the different vibrational levels, with bands originating from higher vibrational levels having higher emission peak altitudes. It is shown that this finding is consistent with the majority of the previously published results. The SCIAMACHY observations yield differences in emission peak altitudes of up to about 4 km between the OH(3-1) and the OH(8-3) band. The observations are complemented by model simulations of the fractional population of the different vibrational levels and of the vibrational level dependence of the emission peak altitude. The model simulations reproduce the observed vibrational level dependence of the emission peak altitude well – both qualitatively and quantitatively – if quenching by atomic oxygen as well as multi-quantum collisional relaxation by O2 is considered. If a linear relationship between emission peak altitude and vibrational level is assumed, then a peak altitude difference of roughly 0.5 km per vibrational level is inferred from both the SCIAMACHY observations and the model simulations.

Vibrational Relaxation of O2(X3Σg–, v = 6–8) by Collisions with O2(X3Σg–, v = 0): Solution of the Problems in the Integrated Profiles Method

The linear kinetic analysis called the integrated profiles method (IPM) makes it simple to analyze the multistep relaxation processes of vibrational manifold. The problem that plots for linear regression in the IPM analysis cannot be made, however, has been found in the study of self relaxation of O2(X3Σ(-)g, v = 6-8). The cause of the problem is the identical time-dependence of the populations of the adjacent vibrational levels. An addition of CF4 into the system made a difference in the time profiles and enabled us to make IPM analysis and determine the rate coefficients. In the experiments, a gaseous mixture of O3/O2/CF4 in an Ar carrier at 298 K was irradiated at 266 nm, and the direct photoproduct O2(X3Σ(-)g, v = 6-9) from O3 was detected by laser-induced fluorescence (LIF)in the B3Σu-X3Σ(-)g transition. Time-resolved LIF intensities of O2(X3Σ(-)g, v) at various pressures of O2 and fixed pressure of CF4 were recorded. The resulting rate coefficients for v = 6−8 correlate smoothly with those for v ≤ 5 and v ≥ 8 reported previously.The vibrational-level dependence (v = 2-13) of the rate coefficients for relaxation of O2(X3Σ(-)g, v) by O2 is accounted for by the balance between the harmonic transition probabilities and the energy defect in the V-V energy-transfer mechanism.

QCT-based vibrational collisional models applied to nonequilibrium nozzle flows

Thermal and chemical nonequilibrium effects are investigated in hypersonic nozzle expanding flows by means of vibrational collisional models. The rate coefficients for rovibrational dissociation and excitation are provided by two chemical databases for the N + N2 system recently developed at NASA Ames Research Center and the University of Bari. Vibrationally averaged rate coefficients for N + N2 collisions are computed based on the hypothesis of equilibrium between translational and rotational modes. N2 + N2 collisions are also considered based on literature data. Inviscid and quasi 1D governing equations are discretized in space by means of a finite volume method. A fully implicit time integration method is applied to obtain steady state solutions. Results show that, for both N + N2 and N2 + N2 collision dominated flows, the populations of vibrational levels deviate from a Boltzmann distribution. An accurate investigation of vibrational level dynamics shows the different behavior of low and high-lying states. Comparison against experimental data acquired at the EAST facility of NASA Ames Research Center demonstrate good agreement between the computed and experimental results.

Model of the vibrational level population of the b 1Σ g + state of oxygen molecules at heights of the lower thermosphere and mesosphere

Model of the vibrational level population of the b 1Σ g + state of oxygen molecules at heights of the lower thermosphere and mesosphere

Model of vibrational level populations of Herzberg states of oxygen molecules at heights of the lower thermosphere and mesosphere

The paper presents a model of the kinetics of electronically excited O2(c1Σu−,v), O2(A′3Δu,v), O2(A3Σu+,v) molecules at heights of the lower thermosphere and mesosphere with allowance for electronic excitation transfer processes during molecular collisions. The model is used to calculate the relative O2(A3Σu+,v) and O2(A′3Δu,v) populations at heights of 80–110 km. The calculated populations are compared with the available literature results on experimental estimates, and good agreement is obtained. It is shown how the increase in the quenching rates of the considered states by oxygen atoms affects the calculation results.

Emission of High Energy during Super-Compressibility of Supersonic Jets

New source of light emission of high energy is found due to arising of instability in supersonic jets. These phenomena are observed in gas jets flowing from the nozzle with a central cone. It leads to high accelerations of the molecules, ions and elementary particles. The emission spectra of the jets are obtained. Decoding of the spectra allowed us to define inverted population of rotational and vibrational levels, electrons temperature, rotational and vibrational temperatures for molecular ions. Internal energy decreasing provides the instability and gas volume decreasing due to internal forces; super-compressibility is result of it; its produce high density of light energy emission in various continuous media.

Luminescence of the B1Σ+–X1Σ+ band system of MgO during plasma electrolytic oxidation of magnesium alloy

A broad luminescence peak with clearly pronounced structure, extending from roughly 19,950cm−1 to 20,400cm−1 is obtained during plasma electrolytic oxidation of magnesium alloy (96% Mg, 3% Al, 1% Zn). It is assigned to the v′−v″=0 band sequence of the B1Σ+–X1Σ+ emission transition of MgO. The measured intensity distribution is combined with quantum-chemical calculations in order to estimate the population of vibrational levels of the upper electronic state, and consequently to determine the plasma temperature. The composition of a plasma containing magnesium, oxygen, and hydrogen under assumption of local thermodynamic equilibrium is calculated in the temperature range up to 12,000K and for pressure of 105, 106, 107, and 108Pa, in order to explain the appearance of the observed spectral features.