FTS Studies Of The Isotopologues Of CO2

Toward Creating A Complete And Highly Accurate Reference Standard

Ben Elliott, Keeyoon Sung, Charles MillerJPL, NASA ORAU

International Symposium On Molecular Spectroscopy18 June 2014

2OCO-2 Retrievals of CO2

• Unsaturated/weak bands in regions dominated by saturated or strongly absorbing features are the most useful for quantifying XCO2

- Features due to the first and even second isotopologues may be completely saturated

- Even strong lines from the lesser species may saturate

• Current CO2 levels have surpassed the XCO2 = 400 ppm mark. Remote sensing missions are requiring higher levels of accuracy from laboratory benchmark measurements

A global fit for rare isotopes:

We need:• Accurate and complete line lists of frequency predictions

• Reasonable intensity estimates of all lines with absorption values above the minimum detection capabilities of remote sensing instrumentation

• Line shapes and contributions from and to nearby lines

• Deconvoluting congested remote retrieval data requires complete and accurate spectroscopic characterization

3Coverage and Remarks on the Isotopologues

MoleculeIsotopologu

e Abundance

HITRAN2012 Spectral Coverage

(cm-1)

HITRAN2012 Number

of Transitions

CO2

626 9.842 10-1 345 - 12785 169 292636 1.106 10-2 406 - 12463 70 611628 3.947 10-3 0 - 9558   116 482627 7.340 10-4 0 - 9600   72 525638 4.434 10-5 489 - 6745   26 737637 8.246 10-6 583 - 6769   2 953828 3.957 10-6 491 - 8161   7 118728 1.472 10-6 626 - 5047   821727 1.368 10-7 535 - 6933   5187838 4.446 10-8 4599 - 4888 

  121

There are 18 total isotopologues available to CO2. Detection capabilities are dependent on abundance and line strength.

Spectral coverage of the 17O enriched isotopologues is significantly less thorough than even the 18O counterparts.

Isotopologue 627 in particular has no laser line data and is significantly undercovered.

13C and 18O isotopologues also need better and more accurate coverage.

4CO2 Line Data

CO2 energy levels form complex polyads due to degeneracy of the bend (n2) and the symmetric stretch (n1).

Frequency data spanning 600 – 8300 cm-1 encompassing multiple polyads have been reported for many isotopologues.

The existing data is used to make identifications of newer more precise data and as a jumping off point for as yet unidentified lines.

OCO-2 Polyad retrieval windows

5CO2 Line Data

Using the data from multiple transitions we can use energy loops to precisely bracket the energies of lesser known states.

Mapping equivalent transitions across all isotopologues allows us to create a frequency grid matrix for future predictions and identification.

6New Data Acquisition at JPLBruker 125HR equipped with and a coolable Herriot cell at JPL

Herriot cell

• New measurements of 17O, 18O, and 13C isotope enriched samples have been taken on the JPL-FTS.

• Regularly achieve line positions accurate to ~5x10-6 cm-1 or better (100 – 150 kHz), nearly an order of magnitude better than the best literature FTS values.

717O-, 18O-, and 13C-Enriched CO2 in the n3 Region

The n3 region of the spectrum provides a reasonable test bed for testing the data and refining the calibration.

CO can be used as a reference standard for calibration of the final spectra in this region.

8Well Resolved Lines and CongestionThe spectra contain

well resolved lines with high signal to noise.

The spectra contain significant contributions from many more isotopologues than desired.

626, 627, and 727 are the main contributors to the 17O-enriched spectrum. 626, 628, and 828 dominate the 18O-enriched spectrum, and 626 and 636 are those for the 13C-enriched.

9CalibrationWe use the highest accuracy CO lines reported by George et al.

and 626 absolute frequency measurements from Shy et al. to bracket the data and obtain the best calibration value.

2000 2050 2100 2150 2200 2250 2300 2350 24000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Wavenumbers, cm-1

Ratio

ed P

eak

Heig

ht, a

rb.

10Calibration ResultThe calibration of the three

separate spectra result in RMS errors of 2.05E-6 cm -1, 1.88E-6 cm -1, and 2.02E-6 cm -1, for 17O-, 18O-, and 13C-enriched spectra, respectively.

We give a conservative estimate of the calibration RMS of 3E-6 cm-1.

Such high quality data is nearing the accuracy levels regularly seen as standard in the microwave spectroscopic techniques, and is an order of magnitude better than previous measurements for most transitions recorded for FTS.

11Assigned Lines 17O-Enriched

2260 2280 2300 2320 2340 2360 23800.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9626627727628728828636637

Wavenumbers, cm-1

Ratio

ed P

eak

Heig

ht, a

rb.

626, 627 and 727 the most prominent contributors.

Significant amounts of 18O present in the sample give 728 and 628 fundamental bands for analysis.

First hotbands of the three main isotopologues are present but peak height is not sufficient to give reliable positions.

12Assigned Lines 18O-Enriched

2220 2240 2260 2280 2300 2320 2340 2360 23800.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

626628828627 728 638 838

Wavenumbers, cm-1

Ratio

ed P

eak

Heig

ht, a

rb.626, 628 and 828 the

most prominent contributors.

Only small amounts of other isotopes present in the sample not having sufficient peak height to give reliable positions.

First hotbands are present but peak height is not sufficient to give reliable positions.

13Assigned Lines 13C-Enriched

2220 2240 2260 2280 2300 2320 2340 2360 23800.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

636 00011-00001636 01111-01101638626

Wavenumbers, cm-1

Ratio

ed P

eak

Heig

ht, a

rb.Only 636 is present in

high enough quantity to give significant peak height.

Even 626 is significantly suppressed.

The first hotband of 636 is present with sufficient peak heights to give reliable positions.

14The Fit of the n3 Region 17O-Enriched

1 J MOL SPEC 189,153–195 ( 1998); 2 IEEE J Quant Elec 22, 234 (1986)

State Constant (cm‑1)

This Work(RMS 0.974)

Claveau et al.(Ref 1)

  Jmax(obs) P63/R66 P72/R7900001

Bv”(10-1) 3.786 135 66(19)

3.786 135 04(23)

  -Dv” (10-7) 1.255 360(94) 1.254 49(8)  Hv” (10-

14)0.869(140) 0.0

       00011

Gv 2340.013 364 0(7)

2340.013 299(1)

  Bv’ (10-1) 3.756 304 02(18)

3.756 303 69(45)

  -Dv’(10-7) 1.252 179(90) 1.251 50(18)  Hv’ (10-14) 0.949(130) 0.4(1)

State Constant (cm‑1)

This Work(RMS 0.970)

Claveau et al.(Ref [1])

Constant (MHz)

This Work(RMS 0.938)

Bradley et al.(Ref [2])

  Jmax(obs) P62/R62 P66/R69 Jmax(obs) P62/R62 P35/R3700001

Bv”(10-1) 3.671 944 77(20)

3.671 946 20(82)

Bv” 11008.213 47(59)  

  -Dv” (10-7) 1.180 735(98) 1.180 53(16) -Dv” (10-3) 3.539 76(29)    Hv” (10-

14)1.080(143) 0.0 Hv” (10-9) 0.324(43)  

             00011

Gv 2330.593 018 1(9)

2330.592 955(9) Gv 69869420.949 2(266)

 

  Bv’ (10-1) 3.643 032 39(19)

3.643 033 93(103)

Bv’ 10921.536 35(57) 10921.535 61(12)

  -Dv’(10-7) 1.177 977(94) 1.177 81(27) -Dv’(10-3) 3.531 49(28) 3.530 96(21)  Hv’ (10-14) 1.375(133) 0.39(20) Hv’ (10-9) 0.412(40) -0.087(150)

State Constant (cm-1)

This Work(RMS 0.954)

Claveau et al.(Ref [1])

  Jmax(obs) P61/R61 P71/R6900001

Bv”(10-1) 3.569 315 96(22) 3.569 318 72(80)

  -Dv” (10-7) 1.116 38(12) 1.115 66(15)  Hv” (10-

14)2.81(19) 0.0

       00011

Gv 2322.434 530 6(10)

2322.434 478(10)

  Bv’ (10-1) 3.541 235 65(22) 3.541 238 15(92)

  -Dv’(10-7) 1.113 71(12) 1.112 92(18)  Hv’ (10-14) 2.64(19) 0.0

627

727

728

15Database Comparison 17O-EnrichedCalculated Line positions versus HITRAN2012

3.6x10-5 cm-1

8.0x10-5 cm-1

16The Fit of the n3 Region 18O-, 13C-Enriched

1 J MOL SPEC 189,153–195 ( 1998); 2 IEEE J Quant Elec 22, 234 (1986)

628

828

636

State Constant (cm‑1)

This Work(RMS 0.968)

17O-Enriched(RMS 0.915)

Constant (MHz)

This Work(RMS 0.968)

Bradley et al.(Ref [2])

Jmax(obs) P67/R67 P59/R59 Jmax(obs) P67/R6700001

Bv”(10-1) 3.681 845 57(18)

3.681 845 58(16)

Bv” 11037.895 34(55)  

  -Dv” (10-7) 1.187 385(80) 1.187 017(42) -Dv” (10-3) 3.559 69(24)    Hv” (10-14) 0.626(103) not fit Hv” (10-9) 0.188(31)               00011

Gv 2332.112 217 3(7)

2332.112 210 4(9)

Gv 69914965.395 5(212)

 

  Bv’ (10-1) 3.652 868 04(18)

3.652 867 99(16)

Bv’ 10951.022 88(55) 10951.022 64(28)

  -Dv’(10-7) 1.184 505(79) 1.184 039(40) -Dv’(10-3) 3.551 05(24) 3.550 91(52)  Hv’ (10-14) 0.834(102) not fit Hv’ (10-9) 0.250(31) 0.074(400)

State Constant (cm‑1)

This Work(RMS 0.928)

Constant (MHz)

This Work(RMS 0.928)

Bradley et al.(Ref [2])

Jmax(obs) P70/R62 P70/R6200001

Bv”(10-1) 3.468 167 81(26)

Bv” 10397.305 52(78)  

  -Dv” (10-7) 1.053 398(130) -Dv” (10-3) 3.158 01(39)    Hv” (10-14) 1.462(173) Hv” (10-9) 0.438(52)             00011

Gv 2314.048 259 8(9)

Gv 69373421.574 5(271)

 

  Bv’ (10-1) 3.440 900 29(27)

Bv’ 10315.559 57(80) 10315.559 54(4)

  -Dv’(10-7) 1.051 112(137) -Dv’(10-3) 3.151 15(41) 3.150 55(6)  Hv’ (10-14) 1.743(187) Hv’ (10-9) 0.523(56) -0.267(39)

State Constant (cm‑1)

This Work(RMS 0.967)

Constant(MHz)

This Work(RMS 0.967)

Bradley et al.(Ref [2])

Jmax(obs) P70/R70 P70/R7000001

Bv”(10-1) 3.902 372 82(20)

Bv” 11699.019 40(61)  

  -Dv” (10-7) 1.333 002(80) -Dv” (10-

3)3.996 24(24)  

  Hv” (10-14) 1.38(9) Hv” (10-9) 0.414(28)             00011

Gv 2283.487 096 3(8)

Gv 68457220.941 3(248)

 

  Bv’ (10-1) 3.872 734 59(20)

Bv’ 11610.166 21(61) 11610.164 90(11)

  -Dv’(10-7) 1.329 266(80) -Dv’(10-3) 3.985 04(24) 3.984 58(14)  Hv’ (10-14) 1.58(9) Hv’ (10-9) 0.475(28) 0.495(72)

17Database Comparison 18O-, and 13C-EnrichedCalculated Line positions versus HITRAN2012

1.7x10-5 cm-1

6.1x10-5 cm-1

18The Fit of the n3 Region Main Isotopologue

626 State Constant(cm‑1)

17O-Enriched(RMS 0.892)

18O-Enriched(RMS 0.888)

13C-Enriched(RMS 0.989)

Jmax(obs) P63/R66 P72/R79 P72/R7900001

Bv”(10-1) 3.902 190 66(27) 3.902 188 81(25) 3.902 189 10(32)

  -Dv” (10-

7)1.334 207(127) 1.333 267(123) 1.333 154(237)

  Hv” (10-

14)2.32(17) 0.303(177) 0.181(490)

         00011

Gv 2349.142 789 8(12)

2349.142 786 8(10)

2349.142 793 1(11)

  Bv’ (10-1) 3.871 415 03(27) 3.871 413 29(25) 3.871 413 48(32)  -Dv’(10-7) 1.330 690(127) 1.329 861(127) 1.329 719(230)  Hv’ (10-14) 2.41(17) 0.728(183) 0.593(470)

Average Difference over J range measured: 1.0x10-6 cm-1

19Conclusions

New data being taken on the FTS at JPL is of high accuracy and precision to the 3x10-6 cm-1 level in line position measurements.

Fits of these new data in the n3 region of the CO2 spectrum have been produced for the 627, 727, 728, 628, 828, and 636 isotopologues, and line lists from them produced. This work helps to addresses a long-standing issue of low coverage of the rarer isotopologues.

Similarly high quality data in the higher energy regions, especially in the 4800 – 6500 cm-1 range, has been recorded and is being processed.

20Acknowledgements

Charles MillerKeeyoon SungLinda BrownBrian DrouinAdam DalyShanshan YuTimothy Crawford

David JacquemartIouli Gordon