Institute for Molecules and Materials
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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 *. SRON January 2007.

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Institute for molecules and materials

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


Institute for molecules and materials

Nijmegen Science Faculty

HFML

NMR pavillion (Kentgens et al.)

HFML

Science faculty: opening 2007

HFML

FEL

NMR


Contents

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 collisionsCIA (Color of liquid oxygen)

    Our approach: cavity ring down spectroscopy

  • Testing and improving LM-theories


Institute for molecules and materials

LM and CIA in O2-A

Why:

‘SRON’ problems:n(z)Air mass (clouds)(Brigtness T)


Institute for molecules and materials

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)


Lm and cia in o 2 a

The O2-A Band (780 nm)

LM and CIA in O2-A


Lm and cia in o 2 a1

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


Institute for molecules and materials

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 . . . .


Lm and cia in o 2 a2

+ 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 psectime in between collisions at 1 Bar: 50 ps


The role of collisions interruption of the coherent interaction hitran

Absorption in between collisions:

The role of collisions: interruption of the ‘coherent’ interaction: HITRAN


From photon molecule interaction to collisions in gases

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


From photon molecule interaction to collisions in gases1

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:


From photon molecule interaction to collisions in gases2

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!


Institute for molecules and materials

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


Lm and cia in o 2 a3

B)

+ h??

If the photon decide to ‘disappear’ when two molecules are ‘intimate’:What happens then?

A reference: collision time 0.2 psectime 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


Institute for molecules and materials

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


Institute for molecules and materials

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


Institute for molecules and materials

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)


Institute for molecules and materials

Cavity Ring Down Spectroscopy

Fit: decay= a*p + b*p2: b contains LM and CIA

Observation

Decay time 

: fixed

Pressure 

CIA!

LM-model


Institute for molecules and materials

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


Institute for molecules and materials

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


Institute for molecules and materials

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)


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