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*
Institute for Molecules and Materials
SRONJanuary
2007+.*St.-Petersburg State University
Nijmegen Science Faculty
NMR pavillion (Kentgens et al.)HFML
Science faculty: opening 2007
HFML
NMRFEL
HFML
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
LM and CIA in O2 -A
LM and CIA in O2-A
Why:
‘SRON’ problems:n(z)Air mass (clouds)(Brigtness T)
LM and CIA in O2-A
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)
WHY ATTENTION FOR LINESHAPES BEYOND HITRAN
LM and CIA in O2-A
The O2-A Band (780 nm)
12850 12900 12950 13000 13050 13100 13150 13200 13250
0,0
2,0x10-4
4,0x10-4
6,0x10-4
8,0x10-4
1,0x10-3
1,2x10-3
1,4x10-3
1,6x10-3
Absorp
tion c
oeff
icie
nt,
cm
-1
atm
-1
Wavenumber, cm-1
A-band of oxygen
LM Model
LM and CIA in O2-A
),',',()780(),,,( 12
32 velrotvelrot vibbOnmhvibXO
Q: How long does photo-absorption take in a molecule ?A: It depends . .
LM and CIA in O2-A
Molecular Eigenstate: energy infinitely precise
Doppler Shift: apparent photon energy changes
Molecular Eigenstate: energy infinitely precise
NCAS
Absorption without collisions
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’)
A Boltzmann distribution without collisions (education) . . . .
0 50 100 150 2000 50 100 150 200
Voigt . . . .
‘time’
LM and CIA in O2-A
)',',()780(
)'',,,()',,,(),,,(1
2
32
32
32
rot
velrotvelrotvelrot
vibbOnmh
vibXOXvibXOXvibXO
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
Frequent interruption of the photo-absorption process.
+ h??
A)
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:
From photon-molecule interaction to collisions in gases . . . .
Absorption in between collisions:
An idea of the formalism:
fi
ifi ti
tEEiiXffXidtG
,
)exp()(
exp..)(
EE
Dipole operator
Line Shape Eigen-
energies
Fourier Transform
If everything is time independent: )()( if EEG
From photon-molecule interaction to collisions in gases . . . .
Absorption in between collisions:
An idea of the formalism:
fi
ifi ti
tEEiiXffXidtG
,
)exp()(
exp..)(
EE
If only i is time dependent and exponentially decaying:
!)( LorentzianG
From photon-molecule interaction to collisions in gases . . . .
fi
ifi ti
tEEiiXffXidtG
,
)exp()(
exp..)(
EE
Absorption in between collisions:
itXtXittidtGi
i )(.)0(.)()exp()( EE
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 . . . . .
Ht
tXHt
tX exp)0(exp)( And the misery starts . . Line mixing!
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
13016 13018 13020 13022 13024 13026 13028
0,0
3,0x10-5
6,0x10-5
9,0x10-5
Abs
orpt
ion,
cm
-1
Wavenumber, cm-1
LM Model, 1 atm LM Model, 5 atm LM Model, 10 atm
12850 12900 12950 13000 13050 13100 13150 13200 13250
0,0
2,0x10-4
4,0x10-4
6,0x10-4
8,0x10-4
1,0x10-3
1,2x10-3
1,4x10-3
1,6x10-3
Abso
rpti
on c
oeff
icie
nt,
cm
-1atm
-1
Wavenumber, cm-1
A-band of oxygen
LM Model
LM and CIA in O2-A
LM and CIA in O2-A
+ h??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
‘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
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
13016 13018 13020 13022 13024 13026 13028
0,0
3,0x10-5
6,0x10-5
9,0x10-5
Abs
orpt
ion,
cm
-1
Wavenumber, cm-1
LM Model, 1 atm LM Model, 5 atm LM Model, 10 atm
Nearly independent of pressure
Nearly quadratic with pressure:one factor is increase in density, one factor is broadening!
0 2 4 6 8 10
0,0
5,0x10-7
1,0x10-6
1,5x10-6
2,0x10-6
2,5x10-6
3,0x10-6
3,5x10-6
Abs
orpt
ion,
cm
-1
Pressure, atm
13016.5 cm-1
LM Model Foigt
Voigt: (Hitran)
LM model
Cavity Ring Down Spectroscopy
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!
The Hunt for LM and CIA in an Experiment:requirements: Very sensitive detection techniqueSignals as function of pressure.
Principle: after a nanosecond light pulse in . . . .Exponential decaying intensity leaking out determined by mirrors and in-cell absorption
Cavity Ring Down Spectroscopy
Pressure D
ecay
tim
e
Fit: decay= a*p + b*p2
a: Rayleigh scatteringb: CIA + Line Mixing (if measured in the far wing)
: fixed
Each point is the result of ONE exponential decay
Cavity Ring Down Spectroscopy
Pressure
Dec
ay t
ime
Fit: decay= a*p + b*p2: b contains LM and CIA
: fixed
13150 13200 13250 13300 13350
0,0
2,0x10-7
4,0x10-7
6,0x10-7
8,0x10-7
1,0x10-6
1,2x10-6
1,4x10-6
1,6x10-6
1,8x10-6 R branch
Bin
ary
abso
rpti
on c
oeff
icie
nt, c
m-1at
m-2
Wavenumber, cm-1atm-2
LM Model Experimental data from different days
LM-model
Observation
CIA!
12850 12900 12950 13000 13050 13100 13150 13200 13250
0,0
2,0x10-4
4,0x10-4
6,0x10-4
8,0x10-4
1,0x10-3
1,2x10-3
1,4x10-3
1,6x10-3
Abso
rpti
on c
oeff
icie
nt,
cm
-1atm
-1
Wavenumber, cm-1
A-band of oxygen
LM Model
Cavity Ring Down Spectroscopy
Pressure
Dec
ay t
ime
Fit: decay= a*p + b*p2: b contains LM and CIA
: fixed
12900 12950 13000 13050 13100 13150 13200 13250 13300 13350
0,0
5,0x10-8
1,0x10-7
1,5x10-7
2,0x10-7
2,5x10-7
Bin
ary
abso
rptio
n co
effi
cien
t, cm
-1at
m-2
Wavenumber, cm-1
Difference between the experimental data and the LM Model - CIA
CIA: smooth no peaks
Above the R branch
In between the P lines An imperfection of ?
12850 12900 12950 13000 13050 13100 13150 13200 13250 13300 13350 13400
0,0
5,0x10-8
1,0x10-7
1,5x10-7
2,0x10-7
2,5x10-7
3,0x10-7
Bin
ary
abso
rptio
n co
effi
cien
t, cm
-1at
m-2
Wavenumber, cm-1
Difference between the experimental data and the LM Model - CIA (French)
Cavity Ring Down Spectroscopy
Pressure
Dec
ay t
ime
Fit: decay= a*p + b*p2: b contains LM and CIA, assuming LM model works
: fixed
Comparison with Tran/Hartmann (JGR, 2006) FT high pressure
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)
