Institute for Molecules and Materials

1. Institute for Molecules and Materials Line mixing and collision induced absorption in the A-band of molecular oxygen: catching oxygen in collisions!Wim J. van der Zande, Maria Kiseleva+, Bas van Lieshout, Marko Kamp, Hans Naus,M. Tonkov*, N.N. Filippov* SRONJanuary 2007 +.*St.-Petersburg State University

2. Nijmegen Science Faculty HFML NMR pavillion (Kentgens et al.) HFML Science faculty: opening 2007 HFML FEL NMR

3. LM and CIA in O2 -A Contents: Why study the A-band of Molecular Oxygen? • Atmospheric relevance and fundamental questions Light – molecule Interaction • From idealized two level systems to absorption in a thermal gas:absorption without collisions: Line shapesabsorption in between collisions: Line Mixing (1948 Bloembergen) absorption during collisions CIA (Color of liquid oxygen) Our approach: cavity ring down spectroscopy • Testing and improving LM-theories

4. LM and CIA in O2-A Why: ‘SRON’ problems:n(z)Air mass (clouds)(Brigtness T)

5. LM and CIA in O2-A WHY ATTENTION FOR LINESHAPES BEYOND HITRAN Effects on Satellite Remote Sensing: (a) 15 m CO2: fluctuations in brightness T of 10 K (b) up to 5% deviation (systematic error) determining photon paths in A-band because of incomplete knowledge of lineshapes (2005, Yang et al, JQRST)

6. The O2-A Band (780 nm) LM and CIA in O2-A

7. Molecular Eigenstate: energy infinitely precise Molecular Eigenstate: energy infinitely precise Doppler Shift: apparent photon energy changes LM and CIA in O2-A Q: How long does photo-absorption take in a molecule ?A: It depends . . LM and CIA in O2-A

8. Absorption without collisions A Boltzmann distribution without collisions (education) . . . . Step one: solve the eigen-energy problem: energies are infinitely well defined Step two: if photon can go in, it also can go out  a finite lifetime of the upper state. The ‘energy’ gets a ‘width’. Step three: the velocity distribution gives an inhomogeneous broadening (each velocity group is ‘independent’) NCAS ‘time’ Voigt . . . . 

9. + h?? LM and CIA in O2-A Q: How long does photo-absorption take in a molecule in a gas ?A: It depends on collision rates or not . . . . LM and CIA in O2-A A) Frequent interruption of the photo-absorption process. B) If the photon decide to ‘disappear’ when two molecules are ‘intimate’:What happens then? A reference: collision time 0.2 psec time in between collisions at 1 Bar: 50 ps

10. Absorption in between collisions: The role of collisions: interruption of the ‘coherent’ interaction: HITRAN

11. Absorption in between collisions: If everything is time independent: From photon-molecule interaction to collisions in gases . . . . An idea of the formalism: Fourier Transform Line Shape Eigen-energies Dipole operator

12. Absorption in between collisions: From photon-molecule interaction to collisions in gases . . . . An idea of the formalism: If only iis time dependent and exponentially decaying:

13. Absorption in between collisions: From photon-molecule interaction to collisions in gases . . . . An idea of the formalism: If you put ‘collisions’ in the Schrodinger Equation, then molecular properties become time dependent. Thus: ‘X’ the dipole operator, and Ei,f is no infinitely defined . . . . . And the misery starts . . Line mixing!

14. Absorption in between collisions: The formalism results only in redistribution of the absorption strength! The line strengths of HITRAN remain good! The line wings become weaker, absorption strength creeps to the center  Atmospheric consequences even in low resolution spectra

15. B) + h?? If the photon decide to ‘disappear’ when two molecules are ‘intimate’:What happens then? A reference: collision time 0.2 psec time in between collisions at 1 Bar: 50 ps LM and CIA in O2-A LM and CIA in O2-A ‘During’ a collision: (I) The Dipole Moment changes in AMPLITUDE(II) The photon energy does not go into the INTERNAL ENERGY only but also redistributes the kinetic energy: no more peaks(III) The relative importance scales with the square of the density/pressure

16. Cavity Ring Down Spectroscopy The Hunt for LM and CIA in an Experiment:Very sensitive detection technique: looking in the line wingsSignals as function of pressure: see below Nearly independent of pressure Voigt: (Hitran) Nearly quadratic with pressure:one factor is increase in density, one factor is broadening! LM model

17. Cavity Ring Down Spectroscopy The Hunt for LM and CIA in an Experiment:requirements: Very sensitive detection techniqueSignals as function of pressure. 50 cm pressure cell, motor driven mirror alignmentpmax=10 BarMirror reflectivity: 99.996%Decay time: 100 s (30 km)Up to 150 times the total oxygen amount in our atmosphere! Principle: after a nanosecond light pulse in . . . .Exponential decaying intensity leaking out determined by mirrors and in-cell absorption

18. Cavity Ring Down Spectroscopy Fit: decay= a*p + b*p2 Each point is the result of ONE exponential decay Decay time  : fixed Pressure  a: Rayleigh scatteringb: CIA + Line Mixing (if measured in the far wing)

19. Cavity Ring Down Spectroscopy Fit: decay= a*p + b*p2: b contains LM and CIA Observation Decay time  : fixed Pressure  CIA! LM-model

20. Cavity Ring Down Spectroscopy Fit: decay= a*p + b*p2: b contains LM and CIA An imperfection of ? In between the P lines Decay time  Above the R branch : fixed Pressure  CIA: smooth no peaks

21. Cavity Ring Down Spectroscopy Fit: decay= a*p + b*p2: b contains LM and CIA, assuming LM model works Decay time  : fixed Pressure  Comparison with Tran/Hartmann (JGR, 2006) FT high pressure

22. Conclusions We have observed FAR WING ABSORPTION . . . . . . . . (1) We detect the combination of LM (line shape details) and CIA(2) We observe that (ABC-model: Tonkov) LM model is reasonable in magnitude, not good in details(3) We are confident that we can improve the Line Shape Determinations(4) CRDS does not have the dynamic range to map the full line-shape (5) As other analyses show, the reduction of the far wing absorption due to LM has a significant impact on satellite retrieval of air mass factors (even in low resolution spectra)