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 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 Coverage and Remarks on the Isotopologues MoleculeIsotopologueAbundance HITRAN2012 Spectral Coverage (cm -1 ) HITRAN2012 Number of Transitions CO 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 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 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 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 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 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 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 Wavenumbers, cm -1 Ratioed Peak Height, arb.

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 Assigned Lines 17 O-Enriched 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 Assigned Lines 18 O-Enriched 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 Assigned Lines 13 C-Enriched 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 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/R B v ”(10 -1 ) (19) (23) -D v ” (10 -7 ) (94) (8) H v ” ( )0.869(140) G v (7) (1) B v ’ (10 -1 ) (18) (45) -D v ’(10 -7 ) (90) (18) H v ’ ( )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/R B v ”(10 -1 ) (20) (82) B v ” (59) -D v ” (10 -7 ) (98) (16)-D v ” (10 -3 ) (29) H v ” ( )1.080(143)0.0 H v ” (10 -9 )0.324(43) G v (9) (9) G v (266) B v ’ (10 -1 ) (19) (103) B v ’ (57) (12) -D v ’(10 -7 ) (94) (27)-D v ’(10 -3 ) (28) (21) H v ’ ( )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/R B v ”(10 -1 ) (22) (80) -D v ” (10 -7 ) (12) (15) H v ” ( )2.81(19) G v (10) (10) B v ’ (10 -1 ) (22) (92) -D v ’(10 -7 ) (12) (18) H v ’ ( )2.64(19)

15 Database Comparison 17 O-Enriched Calculated Line positions versus HITRAN x10 -5 cm x10 -5 cm -1

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) 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/R B v ”(10 -1 ) (18) (16)Bv”Bv” (55) -D v ” (10 -7 ) (80) (42)-D v ” (10 -3 ) (24) H v ” ( )0.626(103)not fitH v ” (10 -9 )0.188(31) 00011GvGv (7) (9)GvGv (212) B v ’ (10 -1 ) (18) (16)Bv’Bv’ (55) (28) -D v ’(10 -7 ) (79) (40)-D v ’(10 -3 ) (24) (52) H v ’ ( )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/R B v ”(10 -1 ) (26)Bv”Bv” (78) -D v ” (10 -7 ) (130)-D v ” (10 -3 ) (39) H v ” ( )1.462(173)H v ” (10 -9 )0.438(52) 00011GvGv (9)GvGv (271) B v ’ (10 -1 ) (27)Bv’Bv’ (80) (4) -D v ’(10 -7 ) (137)-D v ’(10 -3 ) (41) (6) H v ’ ( )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/R B v ”(10 -1 ) (20)Bv”Bv” (61) -D v ” (10 -7 ) (80)-D v ” (10 -3 ) (24) H v ” ( )1.38(9)H v ” (10 -9 )0.414(28) 00011GvGv (8)GvGv (248) B v ’ (10 -1 ) (20)Bv’Bv’ (61) (11) -D v ’(10 -7 ) (80)-D v ’(10 -3 ) (24) (14) H v ’ ( )1.58(9)H v ’ (10 -9 )0.475(28)0.495(72)

17 Database Comparison 18 O-, and 13 C-Enriched Calculated Line positions versus HITRAN x10 -5 cm x10 -5 cm -1

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/R B v ”(10 -1 ) (27) (25) (32) -D v ” (10 -7 ) (127) (123) (237) H v ” ( )2.32(17)0.303(177)0.181(490) 00011GvGv (12) (10) (11) B v ’ (10 -1 ) (27) (25) (32) -D v ’(10 -7 ) (127) (127) (230) H v ’ ( )2.41(17)0.728(183)0.593(470) Average Difference over J range measured: 1.0x10 -6 cm -1

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