ν 3 Q BRANCH OF 12 CH 4 NEAR 33 µm V MALATHY DEVI and D CHRIS BENNER The College of William and Mary Williamsburg VA USA ROBERT R GAMACHE University of Massachusetts Lowell Lowell MA USA ID: 641955
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Slide1
SPECTRAL LINE SHAPES IN THE ν3 Q BRANCH OF 12CH4 NEAR 3.3 µm
V. MALATHY DEVI and D. CHRIS BENNER The College of William and Mary, Williamsburg, VA, U.S.A.ROBERT R. GAMACHE University of Massachusetts Lowell, Lowell, MA, U.S.A.MARY ANN H. SMITH NASA Langley Research Center, Hampton, VA, U.S.A.ROBERT L. SAMS Pacific Northwest National Laboratory, Richland, WA, U.S.A.
FA01
–
72nd
International Symposium on Molecular Spectroscopy, June
19-23, 2017Slide2
2
Present Work: Analyze air-broadened CH4 spectra recorded at room temperature to determine ν3 Q branch line shape parameters needed for terrestrial atmospheric retrievals. Since air-broadened and N2
-broadened line shape parameters for CH
4
are very similar (within 2% according to Tran et al. [2006]), these results are relevant to all planetary atmospheres that are predominantly N2.
Self- and foreign-broadened CH4 line parameters are needed for quantitative analysis of spectroscopic observations of Earth and planetary atmospheres, both to retrieve atmospheric methane abundances and to model the CH4 absorption overlapping features of other species.
Previous lab studies of CH
4
broadening with line mixing have involved mostly P and R branch manifolds, and only a few studies of Q-branches have been reported: most recently
ν
2
+
ν
3
[
Malathy
Devi
et
al
., JQSRT
152 (2015)
149-165] and
2
ν
3
[
Malathy
Devi
et al
., JQSRT 177 (2016) 152-169].
Previous studies of line shapes in the CH
4
ν
3
band system:
See
review of measurements
in the article of Brown
et al
. [
JQSRT
130 (2013) 201-219
] and references therein.
High-resolution
ν
3
Q-branch line mixing
measurements (N
2
, O
2
, H
2
, He,
Ar
, and CH
4
) by Pine [
J. Chem. Phys.
97 (1992)
773-785
] and Pine and
Gabard
[
J. Mol.
Spectrosc
.
217 (2003) 105-114].
Tran
et al
. [JQSRT 101 (2006) 284-305] have
modeled
line mixing for
N
2
- and air-broadening in the
ν
4
and
ν
3
bands, including Q-branches.Slide3
3Summary of Lab Spectra Used in this Analysis
aSpectrum file names are given for authors’ identification. All spectra except #3 were recorded using the McMath-Pierce FTS at a resolution of 0.01 cm-1. Experimental details are in Benner et al. [JQSRT 50 (1993) 65-89].Spectrum #3
was recorded using the
Bruker IFS 120 HR FTS
at Pacific Northwest National Laboratory at a resolution of 0.0011 cm-1. Details of the spectrometer setup are in Malathy Devi et al. [JQSRT 82 (2003)
319-341].1 atm = 101.3kPa = 760 Torr.Serial #Spectraa
Cell length
(m
)
Total Pressure
(
Torr
)
Sample temperature
(K
)
Volume mixing ratio of CH
4
CH
4
1
150x3000.bus
0.25
1.065
296.95
1.0
2
164x3000.bus
1.5
0.408
296.05
1.0
3
922x3000.ars
0.1995
1.068
298.20
1.0
Air-broadened
CH
4
4
154x3000.bus
0.05
75.3
298.25
0.00954
5
153x3000.bus
0.05
150.51
298.35
0.00954
6
152x3000.bus
0.05
301.0
298.35
0.0097
7
151x3000.bus
0.05
500.20
298.25
0.0097
8
149x3000.bus
0.25
50.30
296.75
0.0098
9
148x3000.bus
0.25
125.30
296.65
0.0098
10
147x3000.bus
0.25
250.50
296.55
0.0098
11
146x3000.bus
0.25
400.60
296.35
0.0098
12
163x3000.bus
1.50
60.60
296.15
0.01
13
162x2000.bus
1.50
110.60
296.15
0.01Slide4
Sample Spectra4Resolution:0.01 cm-1 (upper)0.0011 cm-1 (lower)Slide5
5Analysis
Nonlinear least squares multispectrum fitting [Benner et al., JQSRT 53 (1995) 705-721; Letchworth and Benner, JQSRT 107 (2007) 173-192] is used to retrieve spectroscopic parameters consistent with the entire set of laboratory spectra. All spectra are calibrated to the same wavenumber scale
with reference
to H
2O line positions [Benner et al., JQSRT 50 (1993) 65-89].
Initial line list taken from HITRAN2012 [L. S. Rothman et al., JQSRT 130 (2013) 4-50]. Since natural-abundance CH4 samples were used, both 12CH4 and 13CH4
transitions are included.
Voigt
line shape is initially
assumed, and
quadratic speed dependence
is included if residuals indicate it is necessary;
line mixing
is allowed for pairs of lines expected to
mix, or if residuals show evidence of mixing.
Room-temperature
self-broadened spectra
are fit first; then the
air-broadened spectra are added sequentially in order of increasing pressure.Slide6
6Observed Air- and Self-Broadened CH4 Spectra
and Residuals from the Multispectrum FitA total of 13 spectra were fit.Black tick marks in top panel represent the positions of more than 3160 transitions included in the fit.Parameters were retrieved for about 300 transitions of 12CH4
and
13
CH4.Slide7
7Air- and Self-Broadened CH4 Spectra from the Fit: Expanded Scale
Black tick marks at the top of each panel represent the positions of transitions included in the fit.Slide8
8Spectra and Residuals: HITRAN2012 vs. the Multispectrum Fit
A total of 13 spectra were fit.Top panel: Observed spectra. Black tick marks at top represent the positions of more than 3160 transitions included in the fit.Middle panel: Residuals with all line parameters fixed to HITRAN 2012 values.Bottom panel: Residuals from fit to retrieve line parameters for about 300 transitions, including line mixing for 14 pairs of transitions.Slide9
Summary of measured parameters in the Q branch9
a The number of measured positions (in cm-1) is less than the measured line intensities; positions of some transitions were held fixed due to their weakness, blends and proximity to stronger lines.bLine intensity in cm-1/(molecule cm-2)
at 296 K.
c
Lorentz half-width and pressure-shift coefficients and the off-diagonal relaxation matrix elements in units of cm-1
atm-1 at 296 K.d(CH4-air) collisional line mixing coefficients were measured for 14 transition pairs.Parameters
Number of measurements
(
12
CH
4
)
Parameters
Number of measurements
(
13
CH
4
)
Position
(
ν
)
a
252
Position
(
ν
)
a
50
Intensity (S)
b
274
Intensity (S)b51Lorentz air-broadened half-width coefficientc (bL0)103Air-pressure-shiftcoefficientc (86Off-diagonal relaxation matrix element coefficientsc,d(CH4-air) collisions 14
Parameters
Number of measurements
(
12
CH
4
)
Parameters
Number of measurements
(
13
CH
4
)
Position
(
ν
)
a
252
Position
(
ν
)
a
50
Intensity (S)
b
274
Intensity (
S)
b
51
Lorentz air-broadened half-width
coefficient
c
(b
L
0
)
103
86
Off-diagonal relaxation matrix element
coefficients
c,d
(CH
4
-air) collisions
14
Slide10
10Results: Comparison with HITRAN2012 parametersSlide11
11Results: Comparison of Air-Broadening Coefficients
References: Rothman et al. [JQSRT 130 (2013) 4-50]; Pine and Gabard [J. Mol. Spectrosc. 217 (2003) 105-114]. Mean ratios are PS/(Other Ref.).Slide12
12Results: Comparison of Line Mixing Parametersa
See Brown et al. [JQSRT 130 (2013) 201-219].bLine positions from present study.cThe off-diagonal relaxation matrix element coefficients measured for the CH4-air collision system in the present study. dThe off-diagonal relaxation matrix element coefficients calculated
for
the CH
4-air collision system using the formalism in Tran et al. [JQSRT 101
(2006) 284-305].Quantum IdentificationaLine positionb
Off-diagonal relaxation matrix elements,
W
ij
(cm
-
1
atm
-
1
at 296 K)
J
′
C
′
a
′
J
″
C
″
a
″
(
cm-1)CH4-air Meas.cCH4-air Calc.d12 F1 4412 F2 4612 F2 112 F1 23012.029219(7)2012.062725(7)0.00166(13)Not available13 F1 5113 F2 5013 F2 313 F1 43012.503417(11)3012.710279(10)0.01797(69)Not available12 F2 4712 F1 4612 F1 312 F2 33013.511448(8)3013.407770(7)0.01778(19)Not available12 A2 1512 A1 1712 A1 212 A2 13013.592598(5)3013.167070(6)0.02735(45)0.0118611 F1 4411 F2 42
11 F2 3
11 F1 3
3014.060488(5)
3014.344097(9)
0.02846(36)
0.01020
10 F1 39
10 F2 39
10 F2 2
10 F1 1
3014.095407(4)
3014.171700(4)
0.00255(11)
0.00058
10 F2 40
10 F1 38
10 F1 2
10 F2 1
3014.838247(4)
3015.091512(4)
0.01794(32)
0.00101
9 F2 35
9 F1 36
9 F1 3
9 F2 2
3015.590760(4)
3015.706192(4)
0.01447(17)
0.00714
6 A1 9
6 A2 8
6 A2 1
6 A1 1
3016.565296(3)
3017.466013(2)
0.00679(29)
0.00723
7 F1 29
7 F2 27
7 F2 2
7 F1 2
3016.640437(3)
3016.939553(3)
0.00658(15)
0.00509
5 F219
5 F1 21
5 F1 1
5 F2 1
3017.163091(4)
3017.266616(3)
0.00381(10)
0.00029
6 F1 23
6 F2 25
6 F2 2
6 F1 1
3017.227925(3)
3017.345780(3)
0.01179(11)
0.00451
2 F1 8
1 F2 5
2 F2 1
1 F1 1
3018.650122(3)
3018.824378(3)
0.00434(10)
0.00433
3 F2 12
3 F1 14
3 F1 1
3 F2 1
3018.242053(3)
3018.358514(3)
0.00309(7)
0.00359Slide13
13SummaryThe present study reports
the first experimental measurements of air-broadened half-width and pressure shift coefficients for the ν3 band Q branch transitions of 12CH4. Also the first experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing involving CH4-air collisions.Line
positions and intensities
were also measured for
over 250 12CH4 and 50
13CH4 transitions in the Q branch region (3000-3023 cm-1), by applying a multispectrum fitting technique to 13 room-temperature spectra recorded with two different Fourier transform spectrometers.
Future Work
Expand
the
analysis to include other
air- and self-broadened laboratory spectra in
the
ν
3
region recorded at lower temperatures.
Pursue
similar efforts involving other
broadening gases such as H
2
, N
2
,
CO
2
and
He,
including temperature dependences of width, shift and line mixing coefficients.
Final results will be
contributed
future spectroscopic database
updates.Slide14
14Acknowledgments
The research at NASA Langley Research Center, and the College of William and Mary (Grant NNX15AM01G) is supported by the Atmospheric Composition Laboratory Research program of the National Aeronautics and Space Administration. Research performed at the University of Massachusetts Lowell is supported by the National Science Foundation through Grant No. AGS-1622676.We thank Mike Dulick, Detrick Branston, Claude Plymate and the late Jeremy Wagner of the National Solar Observatory for their assistance in recording spectra at Kitt Peak over many years. NSO is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under contract with the National Science Foundation.