Deactivation of Vibrationally Excited Carbon Dioxide (ν3) by Collisions with Carbon Dioxide or with Nitrogen

The relaxation of sulfur hexafluoride has been monitored by observation of infrared absorption intensities following passage of an infrared laser pulse through the gas. The laser pulse saturates a small number of rotational lines in the va<--O transition of SF6 at 944 cml , producing a transient "hole" in the absorption spectrum at that frequency. This hole is filled in very rapidly by rotational relaxation processes. The specific vibrational excitation is, at essentially the same time, transformed into a vibrational temperature in excess of the gas's translational temperature, by means of very efficient vibration .... vibration energy transfer collisions. The energy released in this step also heats the gas translationally by the order of 25°K. The vibrational temperature then relaxes to the translational temperature by a binary collision process, with pr= (122±8) ~sec·torr in pure SF 6 . The rate-controlling step is concluded to be the vibration->translation relaxation of the v. level at 363 cml . The mean efficiency per collision of this step has been measured for He, Ne, Ar, Kr, C2HG, (CHa)20, CH., CHaBr, CHF2Cl, H20, H2, N2, and Cb,inadditionto SF6itself. A transient absorption spectrum arising from the vibrationally hot SF 6 is also given. The slowest relaxation observed in the system is the bulk cooling of the translational temperature of the gas, which occurs in the order of milliseconds under typical experimental conditions. The dominant mechanism for this relaxation appears to be cooling by thermal conduction.

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“…27 A typical example is shown in Fig. A similar type of behavior has been observed in CO2 fluorescence experiments.…”

Section: Transient Absorption Effectssupporting

confidence: 72%

Infrared Double Resonance in Sulfur Hexafluoride

Steinfeld

Burak

Sutton

et al. 1970

The Journal of Chemical Physics

237

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“…They probably appear from two different mechanisms influenced by the buffer gas pressure. A similar type of behaviour has been seen in vibrational relaxation data in pure SF 6 [32] and in CO 2 fluorescence measurements [33].…”

Section: (A) the Functional Dependence Of I (M)supporting

confidence: 79%

A Simple Detector for Measuring the Density of Air Using an α-Ray Source

Matsumoto

Toyooka

1993

Jpn. J. Appl. Phys.

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The IR pulsed photoacoustic method was used to investigate rotational relaxation processes in MPA. We have examined the bulk rotational relaxation times (t R ) and the bulk rotational relaxation cross sections (σ R ), related to R-R and R-T relaxation mechanisms. The saturation intensities for SF 6 gas molecules have been measured in the gas mixtures with CH 4 (buffer) molecules, at constant SF 6 gas pressure (0.47 mbar) and variable CH 4 gas pressure (1-140 mbar), using the 10P(16) CO 2 laser line in the fluences range 0.1-0.7 J cm −2 . It has been found that for proper investigation of the rotational relaxation processes, the buffer gas pressure range must be divided into two parts: the low pressure range (0-20 mbar) and the high pressure range (20-140 mbar), according to the behaviour of the saturation intensities versus buffer gas pressure. Consequently, two different sets of values for rotational relaxation parameters are obtained. The found step-function behaviour for σ R shows that the rotational hole-filling effect during MPA only dominates at low buffer gas pressure (p CH 4 20 mbar). At higher buffer gas pressures (between 20-140 mbar) collisional deactivation takes place. We also derive the enhanced absorption cross sections for absorbing SF 6 gas molecules from the measured saturation intensities data (at zero buffer gas pressure) confirming the expectation that the enhanced absorbing cross sections are not only a function of laser fluence and buffer gas pressure, but are very strongly dependent on laser beam parameters, too.

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“…3 The good agreement between the calculated 3 and experimental 5 values leaves no room for ambiguity.…”

Section: ͑2͒mentioning

confidence: 99%

Near-resonant energy transfer from highly vibrationally excited OH to N2

Burtt

Sharma

2008

The Journal of Chemical Physics

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The probability per collision P͑T͒ of near-resonant vibration-to-vibration energy transfer ͑ET͒ of one quantum of vibrational energy from vibrational levels = 8 and = 9 of OH to N 2 ͑ =0͒, OH͑͒ +N 2 ͑0͒ → OH͑ −1͒ +N 2 ͑1͒, is calculated in the 100-350 K temperature range. These processes represent important steps in a model that explains the enhanced 4.3 m emission from CO 2 in the nocturnal mesosphere. The calculated energy transfer is mediated by weak long-range dipole-quadrupole interaction. The results of this calculation are very sensitive to the strength of the two transition moments. Because of the long range of the intermolecular potential, the resonance function, a measure of energy that can be efficiently exchanged between translation and vibration-rotation degrees of freedom, is rather narrow. A narrow resonance function coupled with the large rotational constant of OH is shown to render the results of the calculation very sensitive to the rotational distribution, or the rotational temperature if one exists, of this molecule. The calculations are carried out in the first and second orders of perturbation theory with the latter shown to give ET probabilities that are an order of magnitude larger than the former. The reasons for the difference in magnitude and temperature dependence of the first-and second-order calculations are discussed. The results of the calculations are compared with room temperature measurements as well as with an earlier calculation. Our calculated results are in good agreement with the room temperature measurements for the transfer of vibrational energy for the exothermic OH͑ =9͒ ET process but are about an order lower than the room temperature measurements for the exothermic OH͑ =8͒ ET process. The cause of this discrepancy is explored. This calculation does not give the large values of the rate coefficients needed by the model that explains the enhanced 4.3 m emission from CO 2 in the nocturnal mesosphere.

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Deactivation of Vibrationally Excited Carbon Dioxide (ν3) by Collisions with Carbon Dioxide or with Nitrogen

Cited by 178 publications

References 13 publications

Infrared Double Resonance in Sulfur Hexafluoride

Infrared Double Resonance in Sulfur Hexafluoride

A Simple Detector for Measuring the Density of Air Using an α-Ray Source

Near-resonant energy transfer from highly vibrationally excited OH to N2

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