1. FTS Studies Of The Isotopologues Of CO 2 Toward Creating A Complete And Highly Accurate Reference Standard Ben Elliott, Keeyoon Sung, Charles Miller JPL, NASA ORAU International Symposium On Molecular Spectroscopy 18 June 2014

2. 2 OCO-2 Retrievals of CO 2 Unsaturated/weak bands in regions dominated by saturated or strongly absorbing features are the most useful for quantifying X CO 2 - Features due to the first and even second isotopologues may be completely saturated - Even strong lines from the lesser species may saturate Current CO 2 levels have surpassed the X CO 2 = 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

3. 3 Coverage and Remarks on the Isotopologues MoleculeIsotopologueAbundance HITRAN2012 Spectral Coverage (cm -1 ) HITRAN2012 Number of Transitions CO 2 6269.842 10 -1 345 - 12785169 292 6361.106 10 -2 406 - 1246370 611 6283.947 10 -3 0 - 9558 116 482 6277.340 10 -4 0 - 9600 72 525 6384.434 10 -5 489 - 6745 26 737 6378.246 10 -6 583 - 6769 2 953 8283.957 10 -6 491 - 8161 7 118 7281.472 10 -6 626 - 5047 821 7271.368 10 -7 535 - 6933 5187 8384.446 10 -8 4599 - 4888 121 There are 18 total isotopologues available to CO 2. Detection capabilities are dependent on abundance and line strength. Spectral coverage of the 17 O enriched isotopologues is significantly less thorough than even the 18 O counterparts. Isotopologue 627 in particular has no laser line data and is significantly undercovered. 13 C and 18 O isotopologues also need better and more accurate coverage.

4. 4 CO 2 Line Data CO 2 energy levels form complex polyads due to degeneracy of the bend ( 2 ) and the symmetric stretch ( 1 ). 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

5. 5 CO 2 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.

6. 6 New Data Acquisition at JPL Bruker 125HR equipped with and a coolable Herriot cell at JPL Herriot cell New measurements of 17 O, 18 O, and 13 C 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.

7. 7 17 O-, 18 O-, and 13 C-Enriched CO 2 in the 3 Region The 3 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.

8. 8 Well Resolved Lines and Congestion The 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 17 O-enriched spectrum. 626, 628, and 828 dominate the 18 O-enriched spectrum, and 626 and 636 are those for the 13 C-enriched.

9. 9 Calibration We 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. 200020502100215022002250230023502400 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Wavenumbers, cm -1 Ratioed Peak Height, arb.

10. 10 Calibration Result The 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 17 O-, 18 O-, and 13 C-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.

11. 11 Assigned Lines 17 O-Enriched 2260228023002320234023602380 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 626 627 727 628 728 828 636 637 Wavenumbers, cm -1 Ratioed Peak Height, arb. 626, 627 and 727 the most prominent contributors. Significant amounts of 18 O 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.

12. 12 Assigned Lines 18 O-Enriched 222022402260228023002320234023602380 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 626 628 828 627 728 638 838 Wavenumbers, cm -1 Ratioed Peak Height, arb. 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.

13. 13 Assigned Lines 13 C-Enriched 222022402260228023002320234023602380 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 636 00011-00001 636 01111-01101 638 626 Wavenumbers, cm -1 Ratioed Peak Height, arb. 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.

14. 14 The Fit of the 3 Region 17 O-Enriched 1 J MOL SPEC 189,153–195 ( 1998); 2 IEEE J Quant Elec 22, 234 (1986) StateConstant (cm ‑ 1 ) This Work (RMS 0.974) Claveau et al. (Ref 1) J max (obs)P63/R66P72/R79 00001 B v ”(10 -1 )3.786 135 66(19)3.786 135 04(23) -D v ” (10 -7 )1.255 360(94)1.254 49(8) H v ” (10 -14 )0.869(140)0.0 00011 G v 2340.013 364 0(7)2340.013 299(1) B v ’ (10 -1 )3.756 304 02(18)3.756 303 69(45) -D v ’(10 -7 )1.252 179(90)1.251 50(18) H v ’ (10 -14 )0.949(130)0.4(1) StateConstant (cm ‑ 1 ) This Work (RMS 0.970) Claveau et al. (Ref [1]) Constant (MHz) This Work (RMS 0.938) Bradley et al. (Ref [2]) J max (obs)P62/R62P66/R69J max (obs)P62/R62P35/R37 00001 B v ”(10 -1 )3.671 944 77(20)3.671 946 20(82) B v ”11008.213 47(59) -D v ” (10 -7 )1.180 735(98)1.180 53(16)-D v ” (10 -3 )3.539 76(29) H v ” (10 -14 )1.080(143)0.0 H v ” (10 -9 )0.324(43) 00011 G v 2330.593 018 1(9)2330.592 955(9) G v 69869420.949 2(266) B v ’ (10 -1 )3.643 032 39(19)3.643 033 93(103) B v ’10921.536 35(57)10921.535 61(12) -D v ’(10 -7 )1.177 977(94)1.177 81(27)-D v ’(10 -3 )3.531 49(28)3.530 96(21) H v ’ (10 -14 )1.375(133)0.39(20) H v ’ (10 -9 )0.412(40)-0.087(150) StateConstant (cm -1 ) This Work (RMS 0.954) Claveau et al. (Ref [1]) J max (obs)P61/R61P71/R69 00001 B v ”(10 -1 )3.569 315 96(22)3.569 318 72(80) -D v ” (10 -7 )1.116 38(12)1.115 66(15) H v ” (10 -14 )2.81(19)0.0 00011 G v 2322.434 530 6(10)2322.434 478(10) B v ’ (10 -1 )3.541 235 65(22)3.541 238 15(92) -D v ’(10 -7 )1.113 71(12)1.112 92(18) H v ’ (10 -14 )2.64(19)0.0 627 727 728

15. 15 Database Comparison 17 O-Enriched Calculated Line positions versus HITRAN2012 3.6x10 -5 cm -1 8.0x10 -5 cm -1

16. 16 The Fit of the 3 Region 18 O-, 13 C-Enriched 1 J MOL SPEC 189,153–195 ( 1998); 2 IEEE J Quant Elec 22, 234 (1986) 628 828 636 StateConstant (cm ‑ 1 ) This Work (RMS 0.968) 17 O-Enriched (RMS 0.915) Constant (MHz) This Work (RMS 0.968) Bradley et al. (Ref [2]) J max (obs)P67/R67P59/R59 J max (obs)P67/R67 00001B v ”(10 -1 )3.681 845 57(18)3.681 845 58(16)Bv”Bv”11037.895 34(55) -D v ” (10 -7 )1.187 385(80)1.187 017(42)-D v ” (10 -3 )3.559 69(24) H v ” (10 -14 )0.626(103)not fitH v ” (10 -9 )0.188(31) 00011GvGv 2332.112 217 3(7)2332.112 210 4(9)GvGv 69914965.395 5(212) B v ’ (10 -1 )3.652 868 04(18)3.652 867 99(16)Bv’Bv’10951.022 88(55)10951.022 64(28) -D v ’(10 -7 )1.184 505(79)1.184 039(40)-D v ’(10 -3 )3.551 05(24)3.550 91(52) H v ’ (10 -14 )0.834(102)not fitH v ’ (10 -9 )0.250(31)0.074(400) StateConstant (cm ‑ 1 ) This Work (RMS 0.928) Constant (MHz) This Work (RMS 0.928) Bradley et al. (Ref [2]) J max (obs)P70/R62 00001B v ”(10 -1 )3.468 167 81(26)Bv”Bv”10397.305 52(78) -D v ” (10 -7 )1.053 398(130)-D v ” (10 -3 )3.158 01(39) H v ” (10 -14 )1.462(173)H v ” (10 -9 )0.438(52) 00011GvGv 2314.048 259 8(9)GvGv 69373421.574 5(271) B v ’ (10 -1 )3.440 900 29(27)Bv’Bv’10315.559 57(80)10315.559 54(4) -D v ’(10 -7 )1.051 112(137)-D v ’(10 -3 )3.151 15(41)3.150 55(6) H v ’ (10 -14 )1.743(187)H v ’ (10 -9 )0.523(56)-0.267(39) StateConstant (cm ‑ 1 ) This Work (RMS 0.967) Constant (MHz) This Work (RMS 0.967) Bradley et al. (Ref [2]) J max (obs)P70/R70 00001B v ”(10 -1 )3.902 372 82(20)Bv”Bv”11699.019 40(61) -D v ” (10 -7 )1.333 002(80)-D v ” (10 -3 )3.996 24(24) H v ” (10 -14 )1.38(9)H v ” (10 -9 )0.414(28) 00011GvGv 2283.487 096 3(8)GvGv 68457220.941 3(248) B v ’ (10 -1 )3.872 734 59(20)Bv’Bv’11610.166 21(61)11610.164 90(11) -D v ’(10 -7 )1.329 266(80)-D v ’(10 -3 )3.985 04(24)3.984 58(14) H v ’ (10 -14 )1.58(9)H v ’ (10 -9 )0.475(28)0.495(72)

17. 17 Database Comparison 18 O-, and 13 C-Enriched Calculated Line positions versus HITRAN2012 1.7x10 -5 cm -1 6.1x10 -5 cm -1

18. 18 The Fit of the 3 Region Main Isotopologue 626 StateConstant (cm ‑ 1 ) 17 O-Enriched (RMS 0.892) 18 O-Enriched (RMS 0.888) 13 C-Enriched (RMS 0.989) J max (obs)P63/R66P72/R79 00001B v ”(10 -1 )3.902 190 66(27)3.902 188 81(25)3.902 189 10(32) -D v ” (10 -7 )1.334 207(127)1.333 267(123)1.333 154(237) H v ” (10 -14 )2.32(17)0.303(177)0.181(490) 00011GvGv 2349.142 789 8(12)2349.142 786 8(10)2349.142 793 1(11) B v ’ (10 -1 )3.871 415 03(27)3.871 413 29(25)3.871 413 48(32) -D v ’(10 -7 )1.330 690(127)1.329 861(127)1.329 719(230) H v ’ (10 -14 )2.41(17)0.728(183)0.593(470) Average Difference over J range measured: 1.0x10 -6 cm -1

19. 19 Conclusions 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 3 region of the CO 2 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.

20. 20 Acknowledgements Charles Miller Keeyoon Sung Linda Brown Brian Drouin Adam Daly Shanshan Yu Timothy Crawford David Jacquemart Iouli Gordon