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Shock tube measurements made between 1 500 and 350 K suggest that O2 is slightly more efficient at deactivating the bending mode of CO2 than is N2. The rate constant for its deactivation by air at 210 K has been estimated.

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... Taine et al. [1978] and Allen et al. [1980] measured the rate of collisions with molecular nitrogen at atmospheric temperatures but only for low-energy vibrational levels. There are also laboratory measurements of this coefficient reported by Simpson et al. [1977], Allen et al. [1977], Taine and Lepoutre [1979], Lunt et al. [1985] and Siddles et al. [1994]. All measurements gave similar values within their experimental errors. ...

... All measurements gave similar values within their experimental errors. Simpson et al. [1977], Taine et al. [1978] and Siddles et al. [1994] also provided the rate of CO 2 (u 2 ) relaxation in collisions with molecular oxygen (see Figure 7). The nominal values for both coefficients (k CO2-air ) used here are the parameterizations of Wintersteiner et al. [1992] obtained by fitting the aforementioned experimental data. ...

The vast set of near-global and continuous atmospheric measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument since 2002, including daytime and nighttime kinetic temperature (Tk) from 20 to 105 km, is available to the scientific community. The temperature is retrieved from SABER measurements of the atmospheric 15 μm CO2 limb emission. This emission separates from local thermodynamic equilibrium (LTE) conditions in the rarefied mesosphere and thermosphere, making it necessary to consider the CO2 vibrational state non-LTE populations in the retrieval algorithm above 70 km. Those populations depend on kinetic parameters describing the rate at which energy exchange between atmospheric molecules take place, but some of these collisional rates are not well known. We consider current uncertainties in the rates of quenching of CO2(υ2) by N2, O2 and O, and the CO2(υ2) vibrational-vibrational exchange to estimate their impact on SABER Tk for different atmospheric conditions. The Tk is more sensitive to the uncertainty in the latter two, and their effects depend on altitude. The Tk combined systematic error due to non-LTE kinetic parameters does not exceed ±1.5 K below 95 km and ±4–5 K at 100 km for most latitudes and seasons (except for polar summer) if the Tk profile does not have pronounced vertical structure. The error is ±3 K at 80 km, ±6 K at 84 km and ±18 K at 100 km under the less favorable polar summer conditions. For strong temperature inversion layers, the errors reach ±3 K at 82 km and ±8 K at 90 km. This particularly affects tide amplitude estimates, with errors of up to ±3 K.

... Appendix A outlines the formulation necessary to incorporate this new 15-/zm cooling scheme in the two-dimensional model. The explicit ratio of Kco2-o and Kco2-co2 is now calculated, with the Kco2-co2 temperature dependence taken from Simpson et al. (1977). An expression for weak Kco2-o temperature dependence, similar to that of Sharma and Nadile (1981), is also given. ...

Recent Pioneer Venus observations have prompted a return to comprehensive hydrodynamical modeling of the thermosphere of Venus. Our approach has been to reexamine the circulation and structure of the thermosphere using the framework of the R. E. Dickinson an E. C. Ridley (1977, Icarus30, 163–178), symmetric two-dimensional model. Sensitivity tests were conducted to see how large-scale winds, eddy diffusion and conduction, and strong 15-μm cooling affect day-night contrasts of densities and temperatures. The calculated densities and temperatures are compared to symmetric empirical model fields constructed from the Pioneer Venus data base. We find that the observed day-to-night variation of composition and temperatures can be derived largely by a wave-drag parameterization that gives a circulation system weaker than predicted prior to Pioneer Venus. The calculated mesospheric winds are consistent with Earth-based observations near 115 km. Our studies also suggest that eddy diffusion is only a minor contributor to the maintenance of observed day and nightside densities, and that eddy coefficients are smaller than values used by previous one-dimensional composition models. The mixing that occurs in the Venus thermosphere results from small-scale and large-scale motions. Strong CO2 15-μm cooling buffers solar perturbation such that the response by the general circulation to solar cycle variation is relatively weak.

... The 4 dependence in the first term implies a temperature-independent cross-section at low temperatures, but our choice of this form is empirical. For collisions of C02 with N 2 and 02, the constants in these expressions were chosen to provide a fit to the published experimental data ( Lunt et al, 1985;Taine et al, 1978;Taine and Lepoutre, 1979;Simpson et al, 1977). Figures 2 and 3 show these data for the deactivation of C0 2 (01101), and our approximations to them. Figure 4 shows the scant data available for the V-T deactivation of C02(02201) by N 2 , and our parameterization. ...

This report describes the development and implementation of models for predicting infrared emission in non-LTE regions of the Earth's atmosphere. Such models are used to stimulate particular atmospheric conditions, both quiescent and aurorally-distributed, in order to extract information from infrared radiance data sets and study the roles of different basic physical processes affecting the upper atmosphere. Specifically, developed is the first line-by-line radiative excitation model for the upper atmosphere, RAD, applied it to the calculation of populations of infrared-active states of CO2 and CO, simulated the conditions of the SPIRE experiments, and elucidated the role of atomic oxygen in exciting the CO2 bending modes. Auroral emissions are modeled and the Field Widened Interferometer data set analyzed using a method of spectral decomposition, and NO band heads identified in the lower-thermosphere emissions. Described are the mathematical procedures underlying the model, especially the RAD model, and the physical process incorporated in them. Results are presented from running the models.

Infrared (IR) planar laser-induced fluorescence (LIF/PLIF) exploits the vibrational level transitions of small gas molecules to achieve spatially-resolved spectroscopic information of the species for combustion and flow-field studies. While typical LIF utilizes electronic excitations with ultraviolet or visible lasers, IR LIF presents an alternative for molecules that are not readily accessible with a conventional UV/visible excitation-collection system. In view of the complexities rooting from longer vibrational level lifetimes and more densely-spaced energy levels, a comprehensive vibrational energy transfer model is developed for state-to-state population evolution and transition process characterization, and a typical CO2/CO/H2O/O2/N2 system relevant to combustion gas mixture is studied by considering a total of 265 energy states and 85,036 transition pathways. The resultant fluorescence signal is thereby studied, with quantitative dependence on local temperature, pressure, gas composition, as well as excitation laser parameters including wavelength, power level and linewidth. Further optimization of collection scheme can be achieved by considering the time-histories and major transition pathways pertaining species evolution on different energy levels. The study develops general modelling and methodology for characterizing the temporal and spectral behavior of a vibrationally-excited molecular system, and demonstrates the potential for quantitative, spatially-resolved diagnostics using IR LIF/PLIF.

This report is a review of the key parameters involved in the calculation of infrared radiation from CO2 in a nuclear environment. These parameters include chemical rate coefficients for the formation/destruction of CO2, rates for collisional excitation/deexcitation of certain vibrational states, and optical parameters including frequencies, Einstein A coefficients and rho Beta factors for bands of CO2 originating from vibrational states up to about 5000 cm-1. The rate coefficients are presented in tabular and graphical form and the optical parameters in tabular form. Uncertainty estimates are provided.

An analysis of the upper atmospheric (80-116 km) CO2(nu-2) vibrational temperatures retrieved from atmospheric trace molecule spectroscopy (ATMOS) experiment Spacelab 3 spectra by using a nonlocal thermodynamic equilibrium (non-LTE) radiative transfer model is presented. Thermal collisions with atmospheric atomic oxygen keep this vibrational state very close to LTE up to around 100 km. Above this height, the different deviations from LTE retrieved from ATMOS/Spacelab 3 spectra for the Northern and the Southern Hemispheres are explained in terms of this collisional process and in terms of the different kinetic temperature profiles measured at those locations. From these simultaneous observations of the kinetic and CO2(nu-2) vibrational temperatures, a deactivation rate of CO2(nu-2) by O(3P) has been derived which leads to a rate coefficient value between 3 and 6 x 10 exp -12 cu cm/s and favors an independent or negative temperature dependence rate constant for the atmospheric temperature range. Cooling rates induced by the CO2 15-micron fundamental band in the upper mesosphere and lower thermosphere were derived from the simultaneous kinetic temperature, CO2(nu-2) vibrational temperature, and CO2 concentration, as measured by ATMOS/Spacelab 3, and found to be a factor of between 5 and 10 times larger than those generally accepted until very recently.

Data from electron gas calculation on the short-range potential and theoretical van der Waals coefficients Cn (n = 6, 8) have been used to construct a potential surface for the Ar+CO2 system. The surface has been used to calculate: second virial coefficient, viscosity and diffusion coefficient, rotational relaxation rates, rate constants for vibrational transitions in CO2 and high-enery/small-angle differential cross sections.

A method for determination of vibrational temperatures in vibrationally-nonequilibrated CO2—laser active medium for CO2, CO and NO admixture molecules is developed and described in this article. The determination of vibrational temperatures of CO and NO molecules is based on spontaneous radiation intensity measurements in the 4.7 and 5.3 μm bands respectively and that of CO2 molecules is based on the simultaneous measurement of radiation intensity in 4.3 and 2.7 μm bands. The CO2 vibrational temperature measurements permitted restoration of the upper (00°1) and lower (10°0) laser levels populations and hence of the gain coefficient in (00°1–10°0) CO2 laser transition.The vibrational temperatures of CO2, CO and NO molecules in CO2-GDL with the introduction of carbon monoxide or nitrogen monoxide instead of nitrogen in the chemically inert 0.1 CO2 + 0.4N2 + 0.5 He and reactive CO + N2O + (N2 + He) mixtures were measured. In these experiments the gain coefficient was measured by two independent methods: by probing laser technique and by restoration of the vibrational temperatures of CO2. The values of gain coefficient and vibrational temperatures were also calculated numerically. This permitted to carry out a comprehensive study of population inversion generation in CO2-GDL on inert and reactive mixtures with additions of CO and NO molecules.

Measurements of the intensity of spontaneous infrared radiation emitted by the active medium of a CO2 gasdynamic laser in the form of bands at 4.3 and 2.7 μ were used to determine the vibrational temperatures of the asymmetric and combination modes of CO2, and to calculate the gain for the 0001 → 1000 laser transition. Measurements were also made of the gain using a probe laser beam. Mixtures of the compositions CO2:N2:He = 1:4:5 and CO2:N2 = 1.9 were investigated for various parameters of the gas in front of the nozzle. A good agreement was obtained between the results of measurements of the gain by two independent methods, which demonstrated that the "spontaneous" method for the diagnostics of CO2 gasdynamic lasers was reliable. Measurements of the vibrational temperatures of gaseous carbon dioxide revealed a more rapid relaxation of the asymmetric CO2 mode than the relaxation predicted theoretically.

Data on the Venus thermosphere from (1) Pioneer Venus Orbiter in situ
measurements and (2) remote sensing of airglow and auroral emissions are
summarized in extensive graphs and diagrams, and empirical models
constructed using the data are reviewed. Particular attention is given
to the emissions of atomic O, O(+), atomic C and C(+), CO and CO(+),
CO2(+), He and He(+), N2 and N2(+), N, NO (nightglow), O2, and O2(+);
hot oxygen and hydrogen coronas and escape; the thermal structure of the
Venus atmosphere; and solar-cycle variation. Thermospheric circulation
and transport phenomena are explored, including symmetric and zonal
features, adiabatic effects, drag processes, thermospheric
superrotation, and the concept of a homopause.

The role of carbon dioxide in cooling the thermospheres of Earth, Venus, and Mars is well recognized (Gordiets et al, 1982; Dickinson, 1984; Dickinson et al, 1987; Dickinson and Bougher, 1986; Bougher and Dickinson, 1988). During a collision of CO{sub 2} with atomic and molecular species, some of the translational energy of relative motion (heat) is converted into vibrational energy of the lowest-lying mode, the bending mode, {nu}{sub 2}. This vibrational energy is subsequently radiated at 15 {mu}m. Many of these photons escape to space, cooling the atmosphere. A new value of the rate coefficient for the deactivation of the bending mode of carbon dioxide by atomic oxygen at low temperatures is derived from the observation of 15 {mu}m emission from the atmosphere of the Earth. This new value gives a cooling rate for the lower thermosphere that is two to three times the rate previously calculated, and it may resolve a long-standing problem in the Mars-Venus aeronomy.

A photoacoustic method is used under such experimental conditions that the (0110) level of CO2 gas is not in equilibrium with the other vibrational levels. The rate constants κ′10 characterizing the CO2 (0110) collisional deactivation by N2, CO and O2 are measured directly.

The rate constant k′21 of the deactivation of the states (0200, 1000)I, (0200, 1000)II and (0220), assumed in mutual equilibrium, towards (0110) is measured between 170 and 300 K; the rate constant k′bs which characterizes the deactivation of all symmetric-stretching and bending levels is measured from 170 to 370 K.

Laser fluorescence has been used to measure rate constants for the vibrational of the bend—stretch manifold of CO2 between 300 and 170 K. The technique employed a pulsed chemical CO laser to produce vibrationally excited CO. This was used in a collisional pumping scheme designed to deposit an excess of vibrational energy in the bend—stretch manifold of CO2. The deactivation of this vibrational manifold has been studied using the following collisional partners: CO2, Ar, Xe, N2 and H2. Our results are compared with the limited amount of other low temperature data which have been published and with data obtained using a shock tube in the temperature range of about 1000 to 400 K. The present low temperature and the published high temperature results extrapolate together smoothly and clearly show the large deviations from Landau—Teller behaviour which occur at low temperatures.

Rate constants for inter- and intra-molecular energy transfer in the N2 + CO2 system are obtained in the temperature range 200–2000 K with three different sets of potential short-range parameters. Comparison with available experimental data is carried out. The analytical solution to the “inversion problem” for the M-quantum case is also presented.

In the present work, we measured the vibrational temperatures of the asymmetric and combined (symmetric and deformation) modes of CO 2 and, therefore, the populations of the upper 00~ and lower 10~ laser leveis of carbon dioxide gas with substitution of nitrogen in the mixture 0.1CO 2 + 0.4N 2 + 0.5He by carbon monoxide or nitrogen oxide. The amplification factor of the weak signal for the laser transition (00~ ~ 10~ was recovered from the values obtained for the population of the Iaser levels. The vibrational tempera~res of CO 2 were determined from measurements of the intensitg of spontaneous IR emission in the 4.3- and 2.7-~m bands using the method in [17]. We simultaneously measured the amplification index with a current probe by an itradiatedprobing CO 2 laser, and the vibrational temperatures of CO and NO according to the intensity of the spontaneous IR emission in the 4.7- and 5.3 #m bands, respectively [17]. The results of measurements of the amplification factor and the vibrational temperatures are compared with the theoretical calculations carried out in the present work. The use of the vibrational temperature measuring method [ 17] assumes a Boltzmann distribution within each mode (or group of modes), described by the corresponding vibrational temperature. In practice, this means that a Boltzmann distribution of molecules must exist in the system of the lower 5-10 levels of the

Time- and spectrally resolved laser-induced fluorescence of CHF(Ã1A″v′2) in single vibronic excited levels (SVL)(0 v′2 5) in the gas phase has been investigated at room temperature. The CHF[X1A′(0,0,0)] source was a microwave discharge in a flow system or multiphoton dissociation (MPD) of CH2F2 in the fluorescence cell. Collision-free lifetimes of the states v′2= 4 and v′2= 5 were measured to be τ0= 1.65 µs and τ0= 1.5 µs, respectively. Deactivation rate constants of CHF[Ã(v′2)], (0 v′2 5), were determined for the quenchers CH2F2(X), He and Ar. Overall deactivation rate constants in [1013 cm3 mol–1 s–1] are: [graphic omitted] increasing with increasing vibrational quantum number. For Ar, the ratio of vibrational to overall deactivation was found to be in the range 0.610–2(kvib/kq) 7.3, i.e. the contribution of vibration deactivation to the overall depletion of the initially excited state is small (10%). Deactivation processes with a vibrational quantum change of Δv′2= 1 and Δ′2= 2, respectively, were determined to be of nearly the same importance.

The heat budget of the region of the upper atmosphere near the mesopause at ~85 km is determined by a balance between radiative, photochemical and dynamical effects leading to a very cold polar mesopause in the summer and a comparatively warm mesopause in the winter. There is a temperature minimum at the mesopause primarily because of the strong radiative cooling which occurs due to thermal emission by carbon dioxide in its v2 vibrational band at 15 µm wavelength. Above 80 km this band is no longer in local thermodynamic equilibrium (LTE) so the amount of cooling depends critically on the rate at which CO2 molecules are excited or relaxed by collision. Any estimate of radiative cooling for this region of the atmosphere, therefore, relies on knowledge of the collisional relaxation time, tau. The importance of the temperature dependence of tau was pointed out by Houghton1. Previous calculations used a wide range of values because no direct measurements of tau had been made in the appropriate temperature range. We show here that the effect on cooling rate calculations of using values of tau measured at temperatures down to 175 K. We also estimate a radiative relaxation time for the atmosphere near the mesopause and are able to draw conclusions as to the natural lifetime of any temperature perturbation at this altitude.

The radiative-excitation algorithm is a completely monochromatic calculation, it includes the detailed layer-by-layer variation of the shapes of the individual lines in its evaluation of atmospheric transmittivity; and, being an iterative algorithm, it avoids the need to construct and invert large matrices, so that a fine layering scheme can be implemented. It also includes a simple correction procedure to minimize the most serious error due to having discrete layers. For altitudes above 40 km, we present results of model calculations of CO2(ν2) vibrational temperatures, 15-μm limb spectral radiances, and cooling rates, for the main band as well as for weaker hot and isotopic bands. We compare the predicted limb radiance with earthlimb spectral scans obtained in the SPIRE rocket experiment over Poker Flat, Alaska, and get excellent agreement as a function of both wavelength and tangent height. -from Authors

Radiation intensity and emissivity of the 4.3 and 2.7 μm vibrational- rotational bands of carbon dioxide and of the 4.7 μm band of carbon monoxide have been numerically calculated and experimentally measured over a wide range of parameters of vibrationally nonequilibrium mixtures expanding through the supersonic nozzle of a gasdynamic CO2 laser. Theoretical determination of radiation characteristics of the active CO2 laser medium in the i.r. spectral region, averaged over the rotational structure, has been made by means of the vibrational- rotational band theory using nonequilibrium energy distributions of molecules over vibrational levels reconstructed on the basis of calculations of vibrational relaxation kinetics in the mixture. A study has been carried out of the effect made on the spectral and integral radiation and absorption of the CO2 and CO bands under consideration by the introduction into the CO2 + N2 mixture of water molecules, essentially accelerating the processes of V-T relaxation and by the substitution of carbon monoxide for nitrogen in the CO2 + N2 + He mixture leading to the alteration of the intermolecular V-V exchange course. The conditions under which radiation intensity or emissivity measurements make it possible to realize reliable diagnostics of vibrational-translational and vibrational-vibrational relaxation processes occurring in a gasdynamic active laser medium have been determined.

The investigation of physical-chemical kinetics in high-temperature gases is motivated by its importance in the aerodynamics of hypersonic flight, in upper atmosphere phenomena, in numerous practical applications as well as by the academic interest.

From the viewpoint of aeronomy, the atmosphere can be considered to be a mixture of gases exposed to the electromagnetic spectrum of the sun. An understanding of the dynamical and photochemical processes which occur in this environment requires consideration of atmospheric radiative transfer. For example, the rate of reaction between two constituents generally depends on the local temperature (see Chapter 2), which is a result of the effects of absorption, scattering, and emission of solar and terrestrial radiation. Further, solar radiation of particular energies can dissociate and ionize atmospheric molecules to produce reactive ions and radicals which participate in many of the important atmospheric chemical processes.

The dissociation and relaxation of CO2 has been reexamined in the incident shock wave with the laser-schlieren technique. These new experiments covered 1377-6478 K, and 42-750 Torr, and improvements partly described herein have permitted accurate determination of both rate and incubation time. In general the steady rate measurements are in agreement with other recent determinations. The one anomaly is that the new rates are not fully second order; they vary about 50% over 70-600 Torr. This unexpected feature is actually quite consistent with the recent literature, which shows a similar trend. However, attempts to produce this result with RRKM calculations were unsuccessful. Relaxation times are in agreement with available literature, and incubation time to relaxation time ratios lie between 1.5 and 3 over 4000-6600 K, consistent with findings for other molecules. These ratios are much smaller than those recently derived from reflected-shock experiments by Oehlschlaeger et al. (Z. Phys. Chem. 2005, 219, 555). A simple argument suggests such large values are indeed anomalous, although why they are too large is not clear.

Each of the two energy levels of CO2 at 1388 and 1285 cm−1 is an equal mixture of doubly excited bending mode and singly excited symmetric stretch mode. The collision numbers of these levels for CO2�CO2 collisions are calculated by using the mixed wavefunctions in conjunction with the SSH theory that has been expanded to include two‐quantum transitions. This relaxation is shown to take place via various near resonant V‐V processes at transition rates of the order of 104 sec−1⋅ torr−1. In particular, direct de‐excitation of the lower laser level via singly excited bending mode is shown to be important. An explanation is given for transitions that involve a change of the vibrational angular momentum l, by Δl = ±2. Three independent experiments have measured rates in reasonable agreement with those calculated here Quite striking is the substantial disagreement between these three experiments on the one hand and the published interpretation of the Rhodes—Kelly—Javan (RKJ) experiment on the other. To resolve this discrepancy, the RKJ experiment is analyzed in detail, and a new interpretation is given that explains one of the observed transient effects as caused by stimulated two‐photon processes and the other by rotational relaxation of the upper laser level.

Energy transfer between vibrationally excited CO and CO2 has been used to excite the bending mode of CO2. The rate of deactivation of this mode by CO2 and by Ar has been measured down to 150 K.

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The acoustic absorption in mixtures of CO2 and O2 has been measured for 90%, 80%, and 70% concentrations of O2 at 300 °K. The absorption has been analyzed to extract the rate of energy transfer between the vibration of the bending mode of CO2 and the O2 vibration and the rate at which O2 de‐excites the bending mode of CO2 in a v‐t process. The rate constants for the v‐t de‐excitation of the bending mode of CO2 by O2 was found to be about the same as de‐excitation by CO2. The v‐v exchange between CO2 and O2 increases only slightly from 1.6×105 (sec atm)−1 at 300 °K to 2.5×105 at 600°K.

Vibrational relaxation in CO2-N2 and CO2-O2 mixtures is studied via the optic-acoustic effect.The relaxation of the bending vibration of CO2 by N2 and O2 can be explained by a simple one-step relaxation. For CO2-N2 a relaxation time of 12.8 ± 1.5 μs atm is obtained, for CO2-O2 8.8 ± 0.3 μs atm.The relaxation of the asymmetric stretching vibration of CO2 by N2 can be described by a two-step mechanism. The result of 11.9 ± 0.25 μs atm for the relaxation time is in reasonable agreement with laser-fluorescence results.The frequency and pressure dependences of the relaxation observed in the CO2-O2 mixtures cannot be explained by a two-step mechanism.

Vibrational relaxation times have been measured in CO2 and CO2 mixtures from 360 to 1500 K by a laser-schlieren method. The scatter in the results is small and there is excellent agreement with recent ultrasonic measurements. Within the experimental error the relaxation times for a given pressure are a function of the translational temperature alone and do not depend upon how close the system is to equilibrium. Simple theories of vibrational relaxation do not account for the results satisfactorily. This applies particularly to the temperature coefficients of the relaxation times of CO2 relaxed by H2 and D2. In general it seems that above 1000 K the relaxation time may be controlled largely by the reduced mass of the collision partners while at lower temperatures this may be true for the inert gases, but not for other molecules.

Vibrational relaxation in mixtures of CO2 with 10% He-3, 10% o-D2 or 3% HD was measured in the temperature range 1000-360 K using a shock tube and a laser schlieren system, and results compared with data on other hydrogen isotopes and isomers. There is clear evidence of vibration-rotation exchange between CO2 and n-H2, HD, and D2. An important role of long-range interactions in the coupling reaction is not indicated, since the relaxation of CO2 by p-H2, in which a rotational transition near resonant with the v2 vibration of CO2 is not possible, was found to be temperature-dependent. The high efficiency of HD in relaxing CO2 suggests that the rate of rotational relaxation is a limiting process for H2 and D2 but not for HD. Calculations based on these measurements indicate that the first-order Sharma (1969) model underestimates the coupling rate by a factor of 2.

The optic-acoustic method has been used to study, at 300 K, the vibrational collisional transfers in a CO2CO mixture, after CO2(00°1) or CO (1) has been excited. Parameters, not obtained through optical or thermodynamic techniques (such as flourescence, shockwaves, etc.), are thus determined.

In order to study the thermal vibrational relaxation of CO2, the gas is given a perturbation such that the bending mode, b, and the symmetric-stretching mode, s, remain in equilibrium with each other while the asymmetric stretching mode, a, undergoes a different evolution. Two relaxation times, τVT and τVV, occur in the collisional exchanges of energy: respectively, that of vibration-translation (V-T) between the set bs and the degrees of translation-rotation; and that of vibration-vibration (V-V) between a and bs. A third parameter, G, characterizes the ratio of energies, gained by bs and lost by a, during the V-V exchange. τVT can be obtained from thermodynamic experiments and τVV by a fluorescence technique. The spectrophone method used here allows the simultaneous determination of τVT, τVV and G; one can therefore determine the quantum levels concerned in the exchanges and compute the corresponding transition probabilities.

Vibrational relaxation times in gases are calculated with the method of Zener using an exponential repulsion in a one‐dimensional model. The constants of the interaction potential are determined by fitting it to the data of Hirschfelder, et al. The great effect which some impurities have is accounted for either by their low mass and resultant high velocity or by ``near resonance'' transfers in which the vibrational quantum of the substratum is used partly to excite the vibration of the impurity, only the difference being transferred to translation. However, there are other impurities, the action of which cannot be explained in this manner. The theoretical values for the relaxation times are 10 to 30 times shorter than the experimental ones, which difference may be accounted for by the use of the one‐dimensional model. Macroscopic equations governing the more complex relaxation processes in polyatomic gases and gas mixtures are developed.

Vibrational relaxation has been studied in CO2 and CO2☒Ar mixtures over the temperature range 360°–3000°K using a laser–schlieren method. The purpose of this investigation was to compare the results obtained by this technique with those deduced using a Mach–Zehnder interferometer and to provide further evidence as to whether relaxation times depend upon how far the system is from equilibrium as well as on the translational temperature. Relaxation times measured by these two methods agree well. The laser–schlieren method is the more satisfactory for measuring the rate of relaxation and the Mach–Zehnder for finding the total density change during the process. These new results support the view that relaxation times do not depend upon how far the system is from equilibrium. The measurements using CO2 and CO2☒Ar mixtures show that CO2 is about five times as effective as Ar in causing relaxation at 360°K and two times as effective at 2000°K.

Theoretical and experimental evidence is presented which leads to a vibrational relaxation time appropriate for the v2 vibration of CO2 at 15 μ under atmospheric conditions at 210°K and standard pressure of 6·0 × 10−6sec. The effect of this on the atmospheric cooling rate near 90 km due to emission by CO2 is discussed. It is shown that absorption of solar radiation by the v3 band (at 4·3 μ) and the combination bands of CO2 (at 2·7 μ) leads to a heating rate of about 2°C (12 hr)−1 near 80 km, this being one of the largest contributions to the radiative heating rate at this altitude. The processes by which relaxation from the v3 vibration of CO2 occurs involve vibrationally excited oxygen and the v2 vibration of H2O. The magnitude of heating-rate depends considerably, therefore, on the H2O concentration. For thermal radiative exchange by the v3 band, thermodynamic equilibrium begins to break down at 30 km; its contribution to the radiative budget of the mesosphere is consequently very small.

X to5 s-r ~trn-~, Cannemeyer and de Vries (0.89 +O.IO) X IO5 s-l aim-r, and Tame [7] ako using spectrophone (9.20 kO.65) X IO4 s-l atm-* . (This last value was obtained from the kbs quoted by the author

- Merrillandammegiving

MerrillandAmmegiving(l.lOtO.t3)X to5 s-r ~trn-~, Cannemeyer and de Vries (0.89 +O.IO) X IO5 s-l aim-r, and Tame [7] ako using spectrophone (9.20 kO.65) X IO4 s-l atm-*. (This last value was obtained from the kbs quoted by the author.) An impact tube me~urement by Chevalier and Huetz-Aubert

Ia4 s-1 atm-* _ Although the difference in efficienciesof 02 and N2 is small it seems that 02 does relax CO&-,) faster than does N2_ One cannot expect crude theo-[Ill LT

- C J S M Simpson
- T R D Chandler
- . D C Allen
- T J Price
- C J S M Simpson

gives a rate constant of (5.15 t 0.45) X Ia4 s-1 atm-* _ Although the difference in efficienciesof 02 and N2 is small it seems that 02 does relax CO&-,) faster than does N2_ One cannot expect crude theo-[Ill LT. Houghton, Quart. J. Roy. Met. Sot. 95 (1969) 1. C.J.S.M. Simpson and T.R.D. Chandler, Proc. Roy. Sot. A317 (1970) 265. D.C. Allen, T.J. Price and C.J.S.M. Simpson, Chem. Phys. Letters 45 (1977) 183. C.J.S.M. Simpson, T.R.D. Chandler and AC. Strawson, J. Chem. Phys. 51 (1969) 2214. P. Chevalier and M. Huetz-Hubert, Advan. Mol. Relaxa-tion Processes 2 (1970) 101. J. Taint, Chcm. Phys. Letters 41 (1976) 297. J. Taine, Thesis, l'l'niversitt Pierre et Marie Curie, Paris VI (1976).