Self- and air-broadened line shape parameters in the n2+n3 band of 12CH4:

4500-4630 cm-1

 V. Malathy Devi

Department of Physics The College of William and Mary

Williamsburg, Virginia

International Symposium on Molecular Spectroscopy

69th Meeting - June 16-20, 2014 - Champaign-Urbana, Illinois

ACKNOWLEDGMENTThe research performed at the College of William and Mary, Connecticut College and NASA Langley Research Center was supported by NASA’s ASCENDS program. Part of the research conducted at the Jet Propulsion Laboratory was performed under contract with National Aeronautics and Space Administration. A. Predoi-Cross was funded by the Natural Sciences and Engineering Research Council of Canada.

D. Chris BennerDepartment of Physics, The College of William and Mary,

Williamsburg, Virginia, USA

Mary Ann H. SmithScience Directorate, NASA Langley Research center, Hampton, VA,

USA

Arlan W. Mantz Department of Physics, Astronomy and geophysics, Connecticut

College, Connecticut, USA

Keeyoon Sung, Linda R. Brown, Timothy J. CrawfordJet Propulsion Laboratory, California Institute of Technology,

Pasadena, California,USA

Adriana Predoi-CrossDepartment of Physics and Astronomy, The University of Lethbridge,

4401 University Drive, Lethbridge, Alberta, Canada

co-authors are:

1. Objective

2. Prior studies of the band investigated in this work

3. Experimental details

4. Sample Spectra

5. Instrumental line shape effects

6. Analysis technique

7. Sample multispectrum fits

8. Results

9. Off-diagonal Relaxation Matrix Element Coefficients

10. Summary and Future plans

The following topics will be briefly discussed

ObjectivesThe methane band system in the 2.3-mm region (Octad) is of interest not only for measurements of CH4 atmospheric profiles, but also because it overlaps the spectra of other atmospheric molecules such as CO and HF

The level of accuracy for line shape parameters in the Octad region of both 12CH4 and 12CH4 is less compared to those for the lower polyads, Dyad and Pentad

Information on line shapes for bands in this spectral region do not meet the desired accuracy requirements to support remote sensing applications such as ASCENDS (Active Sensing of CO2 Emissions over Nights, Days and Seasons) retrievals

One of the major goals of this study was to measure the temperature dependences of Lorentz self- and air-broadened halfwidth, pressure-shift and line mixing (off-diagonal relaxation matrix elements) coefficients for transitions in the n2+n3 band of 12CH4

A multispectrum fitting technique to include speed dependent Voigt profile and full line mixing is applied to fit several spectra (room and cold) simultaneously

Prior line shape studies include the following: Multispectrum analysis of 12CH4 in the 4100-4635 cm-1(room temperature air-

broadening) A. Predoi-Cross et al. J. Mol. Spectrosc 236 (2006) 201-215.

Multispectrum analysis of 12CH4 in the 4100-4635 cm-1(room temperature

self-broadening) A. Predoi-Cross et al. J. Mol. Spectrosc 232 (2005) 231-246.

Line mixing effects in the n2+n3 band (room temperature air-broadening). A.

Predoi-Cross et al. J. Mol. Spectrosc. 246 (2007) 65-76.

Air-broadening and pressure shifts in the 2.3 mm region (room temperature air-broadening) V. Malathy Devi et al. J. Mol. Spectrosc 157 (1993) 95-111.

Temperature dependences of Lorentz air-broadening and pressure shifts in the 2.3 mm region. V. Malathy Devi et al. J. Quant Spectrosc Radiat Transfer

51 (1994) 439-465.

Other research groups are investigating N2-broadened line shape

parameters for the Octad bands

Experimental setup and gas conditionsConfiguration and conditions JPL Bruker IFS 125HR FTS

Spectrum Band pass (cm-1) 3750-5200

Light Source Globar

Beam Splitter CaF2

Detector InSb

Resolution (cm-1) (unapodized) 0.005

Maximum Optical Path Difference (cm) 100

Focal length of the collimating lens (mm) 418

Source aperture diameter (mm) 1.0

Sample pressure

Pure CH4 (Torr)

4.5-385

Total sample pressure (Torr) for CH4+air 95-300

Volume mixing ratio

of CH4 in air-broadened spectra

0.04-0.097

Gas sample temperature (K) 298-150

Absorption Path length (cm) 20.38

Cell windows ZnSe

Vacuum box windows KBr (wedged)

Scanning time (h) 3-4

Signal-to-noise ~2000-2500

Calibration standards used H2Oa, COb,CH4b

a Relative calibration of wavenumber scales

with respect to n3 H2O lines [HITRAN12]

b Absolute calibration with respect to CH4

lines [Predoi-Cross et al. J. Mol. Spectrosc. 232 (2005) 231-246]

Summary of Experimental Conditions of Spectra AnalyzedSpectrum # Gas sample Volume

mixing ratioPressure

(Torr)T (K) Calibration

2534 12CH4 1.00 385.0 298.4 0.9999999885

2557 12CH4 1.00 22.20 250.0 0.9999998113

2556 12CH4 1.00 121.51 250.0 0.9999998275

2551 12CH4 1.00 9.90 200.0 0.9999998140

2550 12CH4 1.00 43.95 200.0 0.9999998070

2549 12CH4 1.00 169.00 200.0 0.9999997685

2540 12CH4 1.00 4.52 148.4 0.9999998142

2537 12CH4 1.00 149.06 148.5 0.9999997806

           

2560 12CH4+air 0.055 112.60 250.0 0.9999998276

2559 12CH4+air 0.057 254.58 250.0 0.9999998276

2554 12CH4+air 0.073 148.49 200.0 0.9999998418

2553 12CH4+air 0.074 299.95 200.0 0.9999998269

2543 12CH4+air 0.0965 95.07 148.4 0.9999998048

2544 12CH4+air 0.0413 225.37 148.4 0.9999998232760 Torr = 1 atm =101.325 kPa = 1.01325 barThe 12CH4 sample was 99.95% enriched in 12C

Additional spectra for background and calibration were recorded but not listed here

Three of the 14 spectra analyzed in this studyCell path length = 20.38 cm

(a) Self-broadened 12CH4

spectrum with 385 Torr at 298.4 K

(b) Self-broadened 12CH4 spectrum with 169 Torr at 200 K

(c) 12CH4+air with 225 Torr total pressure and

methane volume mixing ratio of 0.04

The self- and air-broadened Lorentz half widths, self- and air- pressure-induced shift coefficients and their temperature dependences were measured on a line-by-line basis in the constrained multispectrum fits using the following expressions:

and d0 represent pressure broadening and pressure-shift coefficients (in cm-1 atm-1 at 296 K), respectively. bL (p, T) is the Lorentz half width (in cm-1) of the spectral line at pressure p and temperature T, (Gas)(p0, T0) is the Lorentz half width coefficient of the line at the reference pressure p0 (1 atm) and temperature T0 (296 K) of the broadening gas (either air or CH4), and c is the ratio of the partial pressure of CH4 to the total sample pressure in the cell. Temperature dependences of air- and self-broadened half width and pressure-induced shift coefficients were measured separately for each transition in the same fit.

2

000

0

1

000

0 ),)(()1)(,)((),(n

L

n

LL T

TTpselfb

T

TTpairbpTpb

)()1)(( 000 selfairp

)()()( 0000 TTTT

Equations used to retrieve: Lorentz self- and air-broadened widths, shifts and their

temperature variations

Multispectrum fit of the P(4) manifold in n2+n3

Path length = 20.38 cm

(a) Weighted (obs-calc) fit

residuals

(b) Multispectrum fit of 14 spectra on

an expanded (0.8-1.0) vertical

scale

(c) Same as in the above panel (b), but on a (0-1) vertical scale

The short vertical lines are positions of transitions

included in the fit

Multispectrum fit of the R(6) manifold in n2+n3

(a) Weighted (obs-calc) fit residuals; Voigt with speed

dependence

(b) Weighted (obs-calc) fit residuals; Voigt, with speed

dependence and full line mixing

(c) Multispectrum fit (on an expanded vertical scale: top

10%)

(d) Same as in panel (c), plotted on a 0.4-

1.0 vertical scale

The short vertical lines are positions of transitions

included in the fit

Multispectrum fit of the “allowed” Q branch transitions in the n2+n3 band

(a) Weighted (obs-calc) fit residuals

with speed dependence and full

line mixing

(b) Weighted (obs-calc) fit residuals

using the HITRAN12 line parameters

(c) Final fit of all 14 experimental spectra

The short vertical lines are positions of

transitions included in the fit

Comparisons of line positions and

Ratios of line Intensities

Line intensities and Lorentz width and shift coefficients

Comparisons of self- and air- widths and

pressure-shifts coefficients

Comparisons of temperature dependences of

widths and pressure-shifts Coefficients

Sample of measured line parameters

J′ C′ n′a J″ C″n″b Position(cm-1) Sc % err d×103 % err n ()e×103

% err f×103 ′g×105 SDh×102

3 F1 44 4 F2 1 4500.55451( 3)

 

4500.55453(3)i

6.403 0.02 815

629

801i

631j

0.09

1.30

0.40

0.50

820

854

 

0.18

0.40

-11.81(7)

-8.32(12)

-11.5(3)

-8.8(3)

8.13(6)

3.49(11)

69(1)

3 E 29 4 E 1

4501.23934(4) 

4501.23938(3) 

4501.23912(12)

4.181 0.03 761589751i

586j

603k

0.091.300.700.800.58

833867

  

694

0.220.58

  

2.90

-13.80(8) -8.65(24)

-11.9(5)-10.4(4)

-10.91(33)

10.55(8) 5.91(22)

  

-1.35(55)

69(2)

3 F2 42 4 F1 1 4501.30848(3) 

4501.30858(3) 

4501.30828(10)

5.635 0.02 824651816i

657j

673k

0.111.270.500.600.51

825879

  

777

0.240.45

  

2.32

-11.90(8) -8.36(13)

-11.7(4)-10.3(4)

-10.82(32)

9.63(8) 4.59(13)

  

-2.12(53)

54(1)

a Upper state rotational quantum identifications; b Lower state rotational quantum identifications c S corresponds to line intensities in units of 10-22 cm/molecule at 296 K and the % errors are listed in the column next to it.d are the Lorentz half-width coefficients in cm-1 atm-1 at 296 K; self- width coefficients are given at the top of each row and air-width coefficients are listed at the bottom. The corresponding % errors are listed in the column adjacent to their values.e n ( ) represents the temperature dependence exponents of Lorentz half-width coefficients. They have no units. The values at the top of each row correspond to the temperature dependence exponents for self-width coefficients while the bottom values for the air-width coefficients. The % errors are listed under the next columns.f are the pressure-shift coefficients in cm-1 atm-1 at 296 K; self- shift coefficients are given at the top of each row and air-shift coefficients are listed at the bottom. The corresponding errors are given in parentheses next to their values.g values are the temperature dependences of the pressure-shift coefficients expressed in cm-1 atm-1 K-1. Values at top row correspond to self shift coefficients and the bottom for air shift coefficients.h Speed dependence and have no units. i Predoi-Cross et al. JMS 232 9225) 231-246; j Predoi-Cross et al. JMS 236 (2006) 201-215; k Devi et al. JQSRT 51 (1994) 439-465.

Sample of measured off-diagonal relaxation matrix element coefficientsLine

mixing pair (s)

Line ID Line position(cm-1)

Off-diagonal relaxation matrix element coefficients (in cm-1 atm-1 at 296 K)

      Self-broadening

Air-broadening

T-dep.(self-mixing)

T-dep.(air-mixing)

P(4) F 3F1 44←4F2 1 3F2 42←4F1 1

4500.555 4501.310

0.00429(9)  0.0056(5)a

0.00560(8)e

0.00457(29)  0.0019(3)a

0.00128(6)e

0.00436f

0.8(F) 0.8(F) 

0.8(F)e  0.697f

P(3) F 2F1 30←3F2 1 2F2 32←3F1 1

4511.595 4511.929

0.00466(12)  0.0056(3)a

0.00476(37)  0.0050(1)a

0.00437f

0.82(4) 0.88(15)   0.863f

R(6)A 7A2 33←6A1 1 7A1 31←6A2 1

4626.647 4627.634

0.01484(34)  0.0169(11)a

0.0210(1)b

0.0151(1)d

0.01928(8)e

0.01791(79)  0.0178(5)a

0.0198(0)c

0.0154(2)d

0.01789(4)e

0.01548f

0.8(F)     0.960(8)e

0.8(F)     1.063(6)e

0.788f

R(6)F 7F2 94←6F1 1 7F1 96←6F2 2

4626.814 4626.983

0.00946(13)  0.0088(4)a

0.0093(1)b

0.0105(1)d

0.00650(F)e

0.01123(25)  0.0079(2)a

0.0108(0)c

0.0131(1)d

0.0073(F)e

0.00966f

0.8(F)     0.8(F)e

0.8(F)     0.8(F)e

0.747f

a Predoi-Cross et al. (n2+n3)J. Mol. Spectrosc. 246 (2007)

65-76

b Smith et al. (n4) self-broad.J. Quant. Spectrosc. Radiat

Transfer 111 (2010) 1152-1166

c Smith et al. (n4) air-broad.J. Quant. Spectrosc. Radiat

Transfer 110 (2009) 639-653

d Smith et al. (n2) self- and air- broad.

J. Quant. Spectrosc. Radiat Transfer 153 (2014) 217-234

e Devi et al. (2n3)Self- and air-broad.(Ongoing analysis)

f HaTran (2n3) air-broad.Predicted values (Private

communication)

SUMMARY:I14 spectra (self- and air-broadened) recorded between 150-298 K were fitted simultaneously to retrieve widths, shifts, relaxation matrix elements and speed dependence by employing a non-Voigt line shape model

Off-diagonal relaxation matrix elements were measured for 10 pairs of line-mixed transitions

The mean ratio and standard deviation of the Lorentz self- to air-widths coefficients =1.29(8)

For the 22 comparisons made for the strong CH4 line positions, HITRAN12 values are lower by -0.0008(3) cm-1 compared to HITRAN08

Comparisons of positions in HITRAN08 with our earlier study [Predoi-Cross et al. JMS 232 (2005) 231-246] agree within 0.00003(8) cm-1

Present measurements agree with HITRAN08 values within 0.00001(2) cm-1 and 0.00002(1) cm-1 with our earlier study

Self/air Position Intensity Lorentz Width

Pressure-shift

n (width) δ′ (shift) Speeddependence

self 297 337 183 137 111 95 47air - - 98 85 67 51 -

SUMMARY (cont.)• First measurements of temperature dependence exponents for self-broadening and

a combined analysis of both self- and air-broadened spectra for the n2+n3 transitions

• Line positions, absolute line intensities, Lorentz self- and air-broadened widths, shifts, line mixing coefficients as well as their temperature dependences are determined

• Speed dependence parameter was determined for several transitions

• In most cases, temperature dependence exponents for air-broadened width coefficients were slightly larger compared to self-broadened width coefficients for same transitions

• Overall, for a given transition, temperature dependence for self-shift coefficient was larger compared to that for air-shift coefficient

• Even with data taken in the 150 K-298 K range, temperature dependence exponents of line mixing was determinable only for a few cases

Future plans include similar analyses in the 4100-4500 cm-1 region where the stronger Octad bands n1+n4 and n3+n4 occur

THANK YOU