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Collision-Induced Absorption of Oxygen Molecule: CRDS Study at Low Pressure

This study focuses on the Collision-Induced Absorption (CIA) of oxygen, particularly around 630 nm wavelength, measured at very low pressure using Cavity Ring-Down Spectroscopy (CRDS). The results discuss the lineshape of CIA and the effective intermolecular potential states during collision complexes. The study provides insights into the CIA spectrum and proposes a theoretical model to describe the lineshape. Future work includes exploring temperature dependence on the CIA spectrum for potential application in atmosphere monitoring systems.

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Collision-Induced Absorption of Oxygen Molecule: CRDS Study at Low Pressure

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  1. International Symposium on Molecular Spectroscopy 72ND MEETING - JUNE 19-23, 2017 - CHAMPAIGN-URBANA, ILLINOIS P2431 COLLISON-INDUCED ABSORPTION OF OXYGEN MOLECULE AS STUDIED BY HIGH SENSITIVITY SPECTROSCOPY WATARU KASHIHARA, ATSUSHI SHOJI, AKIO KAWAI Department of Chemistry, Tokyo Institute of Technology, Tokyo, Japan

  2. Introduction ■ Collision-Induced absorption (CIA) of oxygen ◇ Absorptionspectra of oxygen[1] ◇ Scheme of CIA • Collision complex • Monomer Monomer Collision complex [1] S.Solomonet al.,1998

  3. Introduction ■ CIA of oxygen in the atmosphere Absorption of solar radiation by CIA of oxygen is small but significant part of the total budget of incoming shortwave radiation. Absorption bands by CIA are used to calibrate the trace gas concentrations measured by an atmosphere monitoring system. However, a theory predicting the lineshape of CIA still remains unknown. ■ Purpose of this study In this study, we measured CIA band of oxygen around 630 nm at very low oxygen pressure by using CRDS(Cavity ring-down spectroscopy). In addition, we discussed the measured lineshape of CIA.

  4. Experimental ■ Cavity ring-down spectroscopy(CRDS) ◇Principle ◇Experimental setup

  5. Resultsand Discussion • ■ Measured CIA of oxygen ◇Numberdensitydependence ◇CIASpectrum around630 nm Wavelength：630 nm Press. ：＜0.5atm [2] T. Hidemori., 2010 Lineshape dose not depend on pressure. =(7.2±0.1)×10-46cm5 molecue-2 Pressure broadening is not observed.

  6. Resultsand Discussion • ■ Measured CIA of oxygen ◇Numberdensitydependence ◇CIASpectrum around630 nm Wavelength：630 nm Press. ：＜0.5atm What is the lineshape of CIA ? [2] T. Hidemori., 2010 Lineshape dose not depend on pressure. =(7.2±0.1)×10-46cm5 molecue-2 Pressure broadening is not observed.

  7. Resultsand Discussion ■ Collision complex ◇Three states of collision complex Effective intermolecularpotential (1)Bound state Oxygen molecules are bound with a clear structure. Energy (2)Metastable state Oxygen molecules are boundby a centrifugal force barrier. r (3)Free state Collision complex of oxygen is transiently generated only during the collision. L : Orbital angular momentum μ:Reduced mass rotation energy

  8. Resultsand Discussion ■ Collision complex ◇Three states of collision complex Effective intermolecularpotential (1)Bound state Oxygen molecules are bound with a clear structure. Energy (2)Metastable state Oxygen molecules are boundby a centrifugal force barrier. r (3)Free state Collision complex of oxygen is transiently generated only during the collision. L : Orbital angular momentum μ:Reduced mass

  9. Resultsand Discussion ■ Collision complex ◇Three states of collision complex Effective intermolecularpotential (1)Bound state Oxygen molecules are bound with a clear structure. Energy (2)Metastable state Oxygen molecules are boundby a centrifugal force barrier. r (3)Free state Collision complex of oxygen is transiently generated only during the collision. L : Orbital angular momentum μ:Reduced mass

  10. Resultsand Discussion ■ Collision complex ◇Three states of collision complex Temperature dependence[3] (1)Bound state (1) Oxygen molecules are bound with a clear structure. (2) (3) (2)Metastable state Oxygen molecules are boundby a centrifugal force barrier. (3)Free state [3] A. A. Vigasin et al., 2000 Collision complex of oxygen is transiently generated only during the collision. Around room temperature ・ Metastable state ・ Freestate ： 30% ： 70%

  11. Resultsand Discussion ■ Approximation model of lineshape • ⇒ Only free state of collision complex is considered.

  12. Resultsand Discussion ■ Model formula

  13. Resultsand Discussion ■ Fitting results ◇ Fitting parameters ◇ Fitting of the measured CIA b-Xtransitionof monomer oxygen

  14. Conclusion ✓ CIAspectrum around 630 nm was measured at low pressure. ✓ It was succeeded to reproduce the measured CIA spectrum. • ✓ This theoretical model can be used to describe the lineshape of CIA of oxygen. Future works ✓ Measuring temperature dependence on CIA spectrum • ✓Application for an atmosphere monitoring system

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