0 band Z Reed O Polyansky J Hodges National Institute of Standards and Technology University College of London Carbon monoxide Line Shapes and Intensities ID: 630674
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Slide1
Line-shapes and intensities of carbon monoxide transitions in the (3 0) band
Z. Reed,* O. Polyansky,† J. Hodges** National Institute of Standards and Technology† University College of LondonSlide2
Carbon monoxide Line Shapes and IntensitiesCarbon monoxide is present in the planetary atmospheres of most planets in this solar system and is a useful probe of atmospheric dynamics CO is an excellent test case for lineshape modelingCO can readily be modeled
theoretically, presenting a possible approach to link optical measurements to the SI without the use of artifact gas standardsSlide3
Previous WorkExtensive study has been performed on self-, nitrogen-, and air-broadened CO in the
,
, and bands [1]
Intensities of the
band have been previously determined [1-3]
Systematic variation from the Voight profile has been revealed, along with deviations from HITRAN2012 line intensities and a dependence on chosen line shape model
[1]
Mondelain
, D., et al., Broadband and highly sensitive comb-assisted cavity ring down spectroscopy of CO near 1.57
μm
with sub-MHz frequency accuracy. Journal of Quantitative Spectroscopy and Radiative Transfer, 2015. 154: p. 35-43
[2]
Wójtewicz
, S., et al., Low pressure line-shape study of self-broadened CO transitions in the (3←0) band. Journal of Quantitative Spectroscopy and Radiative Transfer, 2013. 130: p. 191-200. [3] Henningsen, J., et al., The 0 → 3 Overtone Band of CO: Precise Linestrengths and Broadening Parameters. Journal of Molecular Spectroscopy, 1999. 193(2): p. 354-362. Slide4
frequency
-
stabilized
reference laser
cw
probe laser
cavity stabilization servo
pzt
optical resonator
decay signal
(a)
(b)
time
stabilized comb of
resonant frequencies
n
FSR
= 108 MHz
absorption spectrum
frequency
4
Frequency Stabilized Cavity Ringdown Spectroscopy (FS-CRDS) at NIST Gaithersburg
Hodges, J.T., et al, Rev. Sci.
Instrum
., 2005, 76, 2
1/(c
t)
=
a
0
+
a
(
n
)
time
frequency
I = I
0
exp
-(t/
t
) +
constSlide5
Linking measured line parameters to the SIGas-filled, length-stabilized
ring-down cavity
I2-stabilizedHeNe laser (10 kHz)Probe LaserOptical FrequencyComb
CsClockProbe laser servo
Primary Pressure
Standards
Primary Temperature
Standards
Calibrated
Thermometers (PRT)
Calibrated
Manometers (SRT)
Cavity length
servo
1/(c
t)
=
a
0
+
a
(
n
)
time
frequencySlide6
Measurement of Line Intensity (S) and Absorber Concentration (n)
S
=
∫
a(n
)
d
n
/{
n
∫
g(n)d
n} =
A
/
n
line profile
(unity area)
fitted spectrum area
measured
absorption coefficient
Once the intrinsic property
S
is known, then
n
=
A
/SSlide7
Hartmann-Tran Line ProfileIncludes mechanisms for collisional narrowing, speed dependent narrowing and shifting, and correlation between velocity- and phase- changing collisions
Average broadening
Speed dependent broadening
Average shifting
Speed dependent shifting
Collisional
narrowing
Correlation
η
Average broadening
Speed dependent broadening
Average shifting
Speed dependent shifting
Collisional
narrowing
Correlation
ηSlide8
HTP Profile reduces to:Voight profile (VP) when
,
, , η = 0Nelkin-Ghatak (NGP) when
,
,
η
= 0
Speed-dependent VP when
,
η
= 0
Quadratic speed dependent NGP when
,
η
= 0Where
=
absorber mass
mass
diffusion coefficient
Quadratic approximation
to speed dependence
Complex, normalized
narrowing frequency
Complex profile
Mechanisms: 1) collisional narrowing (hard-collision model), 2) speed-dependent broadening and shifting,
3) partial correlations between velocity-changing and
dephasing
collisionsSlide9
Line Profiles
Measured and fit results of the N
2-broadened 13CO transition P3, measured at a total pressure of 13.33 kPa and 296KUpper panel, measured (symbols) and fit (line) absorption spectrumLower panes show fit residuals and QF values for individual profilesSlide10
Line Profiles
Measured and fit results of the N
2-broadened 13CO transition P3, measured at a total pressure of 13.33 kPa and 296KUpper panel, measured (symbols) and fit (line) absorption spectrumLower panes show fit residuals and QF values for individual profiles
α
(
ν
)=A{Re I (
ν
-
ν
0
) + Y
Im
(I (ν- ν0)) }Where A = fitted area
Y= dimensionless line mixing term Re(I) = real component Im (I)= imaginary componentLine MixingSlide11
Fitted Area Dependence
Relative fitted area of N
2-broadened 13CO transition P3 measured at a total pressure of 13.33 kPa and 296K, as a function of varying line profiles.Voight profile systematically underestimates line areaSlide12
Line Intensity Determination
Once the intrinsic property
S is known, then n = A/S
n
must be known to determine S
NIST
CO in N
2
standard prepared via gravimetric weighing method
11.9858%
±
0.00095 CO in N
2
Slide13
Line Intensity Determination
Linear fit of fitted line areas of N
2-broadened
13CO transition P3 measured at 296K at pressures ranging from 50 torr to 350 torr. Spectra are fitted with SDNGP profile with line mixing.
GP
SDNGP
SDNGP+LM
S (cm
-1
/(
molec
. cm
-2
)1.0146E-25
1.0151E-251.0153E-25
Uncertainty (%)
0.031
0.010
0.0083Slide14
Measurement repeatability
Transition
Transition no.
S (NIST
)
(cm
-1
/(
molec
. cm
-2
)
uncertainty (%)
12C16O P26
1
1.161E-25
0.043
12
C
16
O
P27
2
7.239E-26
0.054
12
C
16
O
P28
3
4.416E-26
0.12
13
C
16O P1
43.77E-26
0.14
13C16O P2
5
7.20E-260.10
13C16
O P36
1.013E-25
0.29
13C16O R0
7
3.972E-260.23
12C18O R4
8
3.26E-260.19
Normalized line strengths determined via repeated experiment (symbols). Error bar represent individual fit uncertainty
Calculated line strengths and combined uncertaintySlide15
Comparison to Literature and TheoryAll electron MRCI calculations with highest available basis set in MOLPROAug-cc-pCV6Z results are extrapolated to complete basis set limitFirst and second order relativistic corrections and adiabatic corrections included
[1] Wójtewicz, S., et al., Low pressure line-shape study of self-broadened CO transitions in the (3←0) band. JQSRT, 2013. 130: p. 191-200.
[2] A. A. Kyuberis, L. Lodi, V. Ebert, N. F. Zobov, J. Tennyson, O. L. Polyansky
Isotope
Transition
Wojtewicz
1
% diff w.r.t NIST
HITRAN
% diff w.r.t NIST
Ab initio
% diff w.r.t NIST
12
C
16
O
P26
-
0.34
-
0.13
P27
-2.51
-
0.67
-
0.06
P28
-3.06
-
0.58
0.05
13
C
16
O
P1
-1.25
10.61
P2
-1.71
10.44
P3
-0.49
10.89
R0
9.44
12
C
18
O
R4
3.28Slide16
Error Budget
Isotope
Transition
Intensity
Uncertainty
(cm
-1
/
(
molec
. cm
-2
)
%
12
C
16
O
P26
1.16E-25
0.043
P27
7.24E-26
0.054
P28
4.42E-26
0.12
13
C
16
O
P1
3.77E-26
0.14
P2
7.20E-26
0.1
P3
1.01E-25
0.29
R0
3.97E-26
0.23
12
C
18
O
R4
3.26E-26
0.19
NIST uncertainties (not including fit)
unc. (%)
unc
2
pressure
5.00E-03
2.50E-05
composition
7.93E-03
6.28E-05
isotopic composition
1.00E-02
1.00E-04
Temperature
5.00E-02
2.50E-03
Pressure zero drift
2.00E-03
4.00E-06
combined (%)
0.05188Slide17
ConclusionsLine strengths of selected 12C16O, 13
C16O, and 12C18O transitions in the (3
0) band measured at highest precision to dateCalculated line strengths vary significantly from HITRAN and previous literature values, but compare well to ab initio calculationsLink to SI and theoretical line strengths demonstrates possible route to artifact-free determination of molecular concentrations, including isotope ratios
Funding: NIST Greenhouse Gas Measurements and Climate Research Program