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					Combining Ab Initio Theory with Experiment 	


    to Obtain Highly Accurate Line Lists	


                    and
Producing Limited Line Lists with Pure Theory

 Timothy J. Lee, Xinchuan Huang, Ryan Fortenberry, and
                   David W. Schwenke
          Space Science and Astrobiology Division
     NASA Ames Research Center, Moffett Field, CA, USA
                         Some Recent &
                         Current Projects
•  High-resolution rovibrational spectroscopy: NH3, CO2, CH3OH, CH3CN, SO2,
   CH3OCH3 (X. Huang, D. W. Schwenke, and others)
•  Highly accurate quartic force fields => spectroscopic data for small
   astrochemistry molecules and their isotopologues: C3H3+, HC2N, C3H+, N2OH+,
   HOCO isomers, etc. (X. Huang, N. Inostroza Pino, R. Fortenberry, and others)
•  Comparison of basis set extrapolation vs. use of explicitly correlated R12 (or
   F12) methods at the CCSD(T) level of theory (E. Valeev and X. Huang)
•  Global warming studies, specifically the radiative efficiency of various
   fluorinated compounds used in industry (P. Bera, J. Francisco, S. Kokkila)
•  Determination of the mechanism for the UV-induced oxidation of pyrimidine/
   water ice mixtures into uracil (P. Bera, S. Sandford, M. Nuevo, S. Milam)
•  Studies of ionic complexes between small astrochemistry molecules and their
   growth into larger ringed organic molecules (P. Bera and M. Head-Gordon)
•  On the use of Morse-Cosine coordinates for variational calculations of
   rovibrational levels and spectroscopic constants with QFFs (R. Fortenberry,X.
   Huang, W. Thiel)
             Early HIFI Spectra	






HIFI spectrum of water and organics in the Orion Nebula	


© ESA, HEXOS, and the HIFI consortium. E. Bergin	


                                   Outline
•  Brief summary of the theoretical approach for computing highly
   accurate ab initio potential energy surfaces (PESs)

•  Brief summary of the empirical refinement procedure to
   improve the PES

•  Illustrative applications to:
    –  NH3
    –  CO2
    –  SO2

•  Example of a limited line list: trans-HOCO

•  Conclusions
               Approach for Accurate Ab Initio
               Potential Energy Surfaces (PESs)
•  Determine “reference” geometry (5Z basis set; include core-correlation)
•  Set up grid of points for a PES about the reference geometry
•  Calculate CCSD(T) energies for the TZ, QZ, and 5Z basis sets
•  Compute ic-ACPF energies (or different higher-order method); TZ or QZ basis
•  Compute core-correlation correction with CCSD(T) and QZ basis set
•  Compute scalar relativity effects at CCSD(T)/TZ level
•  Compute correction for diffuse functions or include explicitly
•  If desired, compute DBOC and non-adiabatic corrections
•  Extrapolate CCSD(T) TZ/QZ/5Z energies to basis set limit
•  Include higher-order correlation, core-correlation, scalar relativity, diffuse
   function corrections (+DBOC)
•  Fit the “local” part of the PES to high precision
•  Combine with the long range part of the PES that allows dissociation
•  Run many tests on the PES to eliminate holes and improve fit (more points;
   low weight “bridge” points; etc.)
 X. Huang, D. W. Schwenke, and T. J. Lee, JCP 129, 214304 (2008); Huang, Schwenke, and Lee, JCP 134, 044320
 (2011); Huang, Schwenke, and Lee, JCP 134, 044321 (2011); X. Huang, D. W. Schwenke, S. Tashkun, and T. J.
 Lee, J. Chem. Phys., 136, 124311 (2012).	


                   Empirical Refinement of
               Potential Energy Surfaces (PESs)
•  Acquire and examine the available high-resolution rovibrational data for the
   molecule of interest and assess its precision (quality)
•  Try to include as many J values as possible (this improves the J dependence of
   our extrapolations); weight the data according to its assessed precision
•  Refinement performed on PES parameters using energy levels that are derived
   from observed rovibrational transitions to within a cutoff (0.02 cm-1 or better)
•  Do not include in the refinement procedure any energy levels that have been
   obtained strictly through rovibrational models (i.e., a rovibrational model
   constructed from observed transitions and then extrapolated)
•  Invariably, the energy levels from these models are not precise enough and
   degrade the empirical refinement
•  Perform many refinements, tests, look for outliers, etc. in order to make the
   refined PES as robust as possible and useful for extrapolating beyond the
   experimental data included.
•  Once completed, work with experimentalists on assigning new spectra, and
   once these have been assigned, go back to step 1.
H. Partridge, and D. W. Schwenke, JCP 106, 4618 (1997); X. Huang, D. W. Schwenke, and T. J. Lee, JCP 129,
214304 (2008); Huang, Schwenke, and Lee, JCP 134, 044320 (2011); Huang, Schwenke, and Lee, JCP 134,
044321 (2011); X. Huang, D. W. Schwenke, S. Tashkun, and T. J. Lee, J. Chem. Phys., 136, 124311 (2012).	


                  Ammonia in the Universe
•     Found in a wide range of celestial environments and objects:
     1.  Cold ISM (ices and mixed ices); 0-100 K
     2.  Uranus, Neptune, Saturn, and Titan; 50-100 K
     3.  External galaxies (NGC 253, etc.); 140-400 K
     4.  Atmosphere of Jupiter; ≈120 K to much hotter nearer the core
     5.  Sgr B2 molecular cloud complex; ≈700 K
     6.  T dwarfs: e.g., Gl 570D (≈800 K), and Gl 229B (≈1000 K)
     7.  L dwarfs; ≈1500K
•     Ammonia’s rovibrational spectrum is highly temperature sensitive due to
      the presence of the umbrella or inversion mode – its spectrum can be used
      to characterize the temperature of its environment.
•     Until recently, knowledge of its rovibrational spectrum is not adequate,
      especially for high temperature environments (i.e., anything over 300 K).
•     Our goal is to produce an accurate line list, with intensities, for NH3 and all
      isotopologues that is high-resolution and reliable for high temperatures – up
      to 20,000 cm-1 above ZPE.
                                Global PESs: NH3
•  We have reported previously on our purely ab initio PES for NH3 (HSL-0), and
   an initial refined PES (HSL-1), refined using high-resolution experimental data.
•  These are global PESs that allow for dissociation to all possible molecular/
   atomic fragments – but the PES is designed for high-resolution spectroscopy,
   not dynamics calculations.
•  For HSL-1, the rms error for 13 HITRAN bands for J=0-2 was 0.023 cm-1; for
   J=3-5 the rms error for each band was ≤0.15 cm-1.
•  For inversion splittings, the rms error was ≤ 0.03 cm-1 for all J values up to 5,
   and ≤ 0.05 cm-1 for J=6.
•  We proposed further work that would improve our PES and allow us to
   compute accurate transition frequencies and intensities up to 20,000 cm-1 above
   the zero-point level:
    –  Inclusion of non-adibatic corrections to reduce the deterioration on going to higher J values
    –  Further refinement including up to J=6 transition frequencies that are reliable
•  In early 2011, we reported a new PES, HSL-2.
X. Huang, D. W. Schwenke, and T. J. Lee, JCP 129, 214304 (2008); Huang, Schwenke, and Lee, JCP 134, 044320 (2011);
Huang, Schwenke, and Lee, JCP 134, 044321 (2011).
                       NH3:
             The HSL-0 and HSL-1 PESs




•    The purely ab initio global PES showed good agreement with experiment
     for a global surface.
•    HSL-1, our first empirically refined PES, showed very good agreement with
     experiment – the best to date of any PES.
•    HSL-1 exhibits deterioration on going to higher J values.
                        NH3:
              The HSL-1 and HSL-2 PESs




•    HSL-2 shows an order of magnitude improvement over HSL-1!
•    The deterioration on going to higher J values is markedly less!
•    The rms error for J=0-6 energy levels is only 0.015 cm-1!
•    For J=7/8 the rms error is only 0.020 and 0.023 cm-1, respectively!
•    The rms error for inversion splittings is about 1/3 that for energy levels!
                        NH3: Highlights of HSL-2
•  Selected J=0-4/6 HITRAN levels used in the PES refinement
•  Non-adiabatic & DBOC correction terms included
•  0.01 ~ 0.02 cm-1 accuracy for J ≤ 8 and energy levels < 5300 cm-1
•  Reproduced most high-resolution HITRAN and CDMS line positions
•  Determined that the experimental 2ν4 models are unreliable
•  Proposed new analysis for some 2ν4 and n3+n4 transitions
•  Identified some missing levels (e.g. 2ν4 62l=0s/a) in existing HITRAN data
•  Identified new bands (e.g. 2ν2+ν4, (ν3+ν4)l=0, etc) in existing HITRAN data
•  Achieved ~10 MHz accuracy for 15NH3 pure inversion-rotational transitions
•  15N Isotopic shifts have been determined for all HITRAN levels.

•  Assessed accuracy of line positions beyond 5300 cm-1 through comparisons
   with work by Lees & Xu, and by comparison with new spectra from Keeyoon
   Sung and Linda Brown (varie between 0.4 to 1.5 cm-1)
•  This latter work has lead to the start of a newly refined PES, HSL-Pre3
Huang, Schwenke, and Lee, JCP 134, 044320 (2011); Huang, Schwenke, and Lee, JCP 134, 044321 (2011);
K. Sung, L. R. Brown, X. Huang, D. W. Schwenke, T. J. Lee, S. L. Coy, and K. K. Lehmann, JQSRT, 113, 1066 (2012).	


.
                    Comparison of New
                JPL Experiments to HSL-Pre3
•  Observed 14NH3 spectrum in top panel
   with 6 computed bands (under
   experimental conditions) below.
•  Sum of intensity for the 6 bands is 63% of
   the total 14NH3 opacity.
•  The bottom panel shows the remaining
   unassigned features.
•  From HSL-1 to HSL-Pre3:
    –  We use 6 J=0/1/2/4/6 A” symmetry blocks, 112
       HITRAN levels + 29 previously analyzed levels
       to refine HSL-1
    –  Final σRMS = 0.019 cm-1
•  We have computed J=0-8 spectra on HSL-
   Pre3 and used this for the synthetic spectra
   at right
•  The level of precision found for HSL-2 for
   < 5300 cm-1 has been expanded to
   approximately 7000 cm-1
•  Work continues on a newly refined PES
                              CO2 : Motivation
•  Venus Express is an ESA mission with NASA participation
•  Venus Express completed its Primary Mission Sept 2007, and Extended
   Mission no. 1 Dec 2009
•  Extended Mission no. 2 extends to Dec 2014 subject to validation in mid-2012
•  Two of the goals of Venus Express are to study the atmospheric dynamics of
   Venus, and to study the atmospheric composition and chemistry
•  CO2 is the principle component of the Venusian atmosphere
•  But the spectroscopy of CO2 is not well characterized under the high
   temperature (750 K) and high pressure (100 bar) conditions present on Venus
•  The current state of knowledge severely limits the analysis of data from the
   PFS and SOIR instruments
•  Our goals:
   –  to use state-of-the art ab initio calculations to construct a global PES for CO2 and to use the
      best high-resolution experimental data to refine the PES (similar to NH3 and H2O)
   –  To compute an accurate dipole moment surface (DMS) and to generate a highly accurate line
      list for CO2 up to 20,000 cm-1 above zero-point
   –  To determine line shape parameters relevant to the conditions on Venus
   –  To repeat this for the other isotopologues of CO2
                                                  Global PES for CO2: Initial
                                                 Empirical Refinement of Ames-0
                                        4                                                                                     4
       -1




                                                                                              -1
        1st refined PES - HITRAN / cm




                                                                                              2nd refined PES - HITRAN / cm
                                        2                                                                                     2



                                        0                                                                                     0



                                        -2                                                                                    -2
                                                  J=0-4                                                                                J = 0 - 10
                                                  J = 0, 5, 10, 15, ..., 95                                                            J = 0, 5, 10, 15, ..., 95
                                        -4                                                                                    -4
                                             0    3000     6000      9000     12000   15000                                        0   3000     6000      9000     12000   15000
                                                                              -1                                                                                   -1
                                                      HITRAN Levels / cm                                                                   HITRAN Levels / cm
•  Initial attempts to refine the PES used J=0-4 and then J=0-10 data from
   HITRAN2008; the increased J data significantly reduced the J dependent errors.
•  As was done with NH3, only up through the quartic constants were allowed to
   vary (22), and the maximum change was less than 2% in all cases.
•  Use of higher J values (>40) was a disaster; the problem is that many of the
   HITRAN2008 energy levels are from models and not experimentally observed.
•  Enter our collaborator Dr. Sergey Tashkun, who has compiled a set of 8142
   experimentally determined energy levels for 12C16O2.
  X. Huang, D. W. Schwenke, S. Tashkun, and T. J. Lee, J. Chem. Phys., 136, 124311 (2012).	


                Global PES for CO2: Refinement
                   using only Expt (Ames-1)




•  Refinement included all J=0,1,2,10,25,40,55,70,85 IR rovibrational levels (471);
   3 levels above 20,000 cm-1 and one J=85 level given smaller weight.
•  We started with the previous J=0-4 refined PES: the change in all 22 coefficients
   was less than 0.7%.
•  The RMS error is reduced from 0.085 cm-1 on the J=0-4 PES to 0.0197 cm-1 for
   Ames-1 for the 467 equally weighted energy levels.
•  RMS errors range from 0.01 to 0.015 cm-1 up to 8000 cm-1, rising to 0.04 cm-1 at
   14,000 cm-1 (J up to 117), with accumulated RMS of 0.0156 cm-1 (6873 levels).
 X. Huang, D. W. Schwenke, S. Tashkun, and T. J. Lee, J. Chem. Phys., 136, 124311 (2012).	


                                   Initial IR Line List
                                   for 12C16O2 at 296K




•  Computed spectra at 296K using Ames-1 PES and Ames-0 DMS.
•  For energies between 500 cm-1 and about 8400 cm-1, agreement for IR intensities
   is reasonable.
•  Some of the differences (<500 cm-1 and around 10,000 cm-1 and 12,000 cm-1) are
   most likely due to a lack of experimental data in these regions.
•  Some of the differences, such as around 1500 cm-1, are probably due to
   deficiencies with the Ames-0 DMS; differences in other regions are not yet clear.
•  Comparison with HITEMP, HOT-CO2, and CDSD leads to similar conclusions.
  X. Huang, D. W. Schwenke, S. Tashkun, and T. J. Lee, J. Chem. Phys., 136, 124311 (2012).	


                                  12C16O :
                                        Ames296 vs.
                                        2
                                  HITEMP and Wattson


                                                                              Computed by Richard
                                                                              Freedman; unpublished. 	






•    Computed spectra at 3000K using Ames-1 PES and Ames-0 DMS.
•    Regions where HITEMP is incomplete and we are complete, but…
•    Regions where our intensities do not agree
•    Similar comparisons with CDSD show that our Ames-0 DMS is lacking
     X. Huang, D. W. Schwenke, S. Tashkun, and T. J. Lee, J. Chem. Phys., 136, 124311 (2012).	


                                              12C16O :    New DMSs
                                                    2


                                1E-16
                                1E-18                                      HITRAN
                                                                           DMS-0Z
     -1
      Intensity / cm.molecule




                                1E-20                                      DMS-N1
                                1E-22                                      DMS-N2
                                                                           DMS-N3
                                1E-24
                                1E-26
                                1E-28
                                1E-30
                                1E-32
                                1E-34
                                        0   3000   6000        9000           12000   15000
                                                                      -1
                                                     Frequency / cm
•    Computed spectra at 296K using the Ames-1 PES and new DMSs.
•    DMS-N2 (or DMS-N1) are preferred; tests show that DMS-N3 is over determined
•    There are significant changes above 11,500 cm-1.
•    Changes around 2000 cm-1 are not large – minor differences in this region.
                                             12C16O ;New DMSs:
                                                   2
                                               9000 cm-1 region

                                                                                HITRAN
                              1E-25                                             DMS-0Z
   -1
    Intensity / cm.molecule




                                                     50014	

   50013	

        DMS-N1
                                                                                DMS-N2
                                                                                DMS-N3
                              1E-27



                              1E-29



                              1E-31
                                      8400    8600   8800          9000          9200    9400
                                                                           -1
                                                        Frequency / cm


•  Computed spectra at 296K using the Ames-1 PES and new DMSs.
•  Still significant disagreement (two orders of magnitude) with HITRAN
•  Which is correct?
                                                      12C16O ;    New DMSs:
                                                            2
                                                            9000 cm-1 region
                                          -26
                                       1x10                                    New Experiments (2012)
             -1
             Intensity / cm.molecule

                                          -27                                  Ames-296K Predictions
                                       8x10
                                                                               Watson Hot-CO2
                                          -27
                                       6x10
                                          -27
                                       4x10
                                          -27
                                       2x10

                                              0
                                              8790   8810   8830      8850   8920   8940   8960    8980   9000
                                                            12   16                           -1
                                                             C O2 Transition Frequency / cm

•    Agreement between Ames-296K and the new experiments is excellent!
•    HITRAN intensities 1/100th the Ames-296K/Expt values; do not appear
•    The Ames-296K values are more accurate than the Wattson Hot-CO2 values also.
•    The Ames-296K list is more complete than the new experiments.
•    New experiments by T.M. Petrova, A.M. Solodov, A.A. Solodov, O.M. Lyulin,
     S.A. Tashkun, and V. I. Perevalov; Presented at The XVII Symposium on High
     Resolution Molecular Spectroscopy in July, 2012.
                       Isotopologues of CO2




•  The Ames-1 PES has been used to compute the J=0 band origins for 13 major
   isotopologues of CO2, including:12C16O2, 13C16O2, 12C18O2, 12C17O2, 13C18O2,
   13C17O , 14C16O , 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 17O12C18O, and
          2       2
   17O13C18O.

•  The RMS error is less than 0.13 cm-1 for all isotopologues
•  For all known Gv values of these isotopologues (minus outliers), the RMS error
   from Ames-1 is 0.08 cm-1, with Emax = 25,865 cm-1
•  Gv outliers were confirmed by comparison of Ames-1 values with those
   obtained from an Effective Hamiltonian model (Tashkun, to be published).
                          SO2 : Motivation
•  SO2 has been identified as a “2nd-class weed” by the HIFI community
•  As such, its lines will obscure those from other (more interesting) molecules in
   various astrophysical environments.
•  It is also an important minor constituent in some planetary atmospheres, such
   as Venus.
                                                             •  There are regions
                                                                where there is no
                                                                CO2 absorption, and
                                                                there is SO2
                                                                absorption but it is
                                                                missing in
                                                                HITRAN.	


                                                             •  This is the spectral
                                                                region covered by
                                                                the high resolution
                                                                SOIR instrument on
                                                                Venus Express	


                               From Ames-0 to Ames-1:
                                      Details	
  
489 selected geometries	


CCSD(T)/(aug-)cc-pV(X+d)Z basis, X=T,Q,5	

                            	
  
                                                                 Refined with 465 selected HITRAN levels	


                                                                 5/43/183/158/57 levels at J=0/4/20/50/70 with
CCSD(T)/aug-cc-pcwVXZ, X=T,Q	

                                  weights: 2.5/1.0/1.5/2.0/3.0. 
CCSD(T)/aug-cc-pV(Q+d)Z dipoles	

                               	


core/scalar relativistic effects
                                                                 80/73/49/47/43/30/22/74/28/ levels from GS/
	


219 unique coeffs, i,j,k ≤ 8, i+j+k ≤ 12, i ≤ j 	

              ν3/2ν3/ν2/ν2+ν3/2ν2/ν1/ν1+ν2 	


Higher weights on ~400 points < 30,000 cm-1	

                   Plus 19 high res band origins.	


	

                                                              	


Initial Ames-0: CCSD(T)/cc-pVQZ-DK	

                            In short, a HITRAN-based refinement 	


For 0 – 30,000 cm-1, 	

                                         	


PES Δ(avg) = 0.21 cm-1 , σRMS = 0.31 cm-1	

                     On the Final Refined Ames-1 PES	


DMS δ(avg) = 1.2E-5 D,         σRMS = 1.96E-5 D	

                   σRMS = 0.024 cm-1 (weighted) 	


DMS δ%(avg) = 0.02%	

                                                      0.010 cm-1 (unweighted)	



E = Long-range terms (Morse-type) + Short-range terms * damping function
           2                             2                                    2   2
                                                                                                  2                 4
VLong = ∑ De1 (1 − e − β ⋅Δri ) 2 + ∑ De 2 (1 − e − β ⋅Δri ) 4 + e −0.2⋅( Δr1 + Δr2 ) ⋅ ( Ae1Δa1 + Ae 2 Δa1 )
          i =1                          i =1
                                                                                       2               2
                  969                                                    −damp1 ∑ ( Δri )2 − damp 2 ∑ ( Δri ) 4 −damp 3⋅( Δα1 ) 2 −damp 4⋅( Δα1 )4
                          n         i          j        k
VShort = f damp ∑ C P[(Δr1 ) ( Δr2 ) ](Δα1 ) , f damp = e
                         ijk
                                                                                      i =1            i =1


                  n =1

De1 = 233,156 cm-1, De2 = 5,250 cm-1, Ae1 = 56,000 cm-1, Ae2 = 50,000 cm-1	


β = 1.152733 Å-1, Δri = ri – 1.43108 Å, Δα1 = cosα(∠OSO)-cos(119.3209°) 	


                                                          SO2 : Relabeling a few
                                                          2ν3/ν1+3ν2 Ka=11 levels
                                                                                                                               After relabeling 9 HITRAN levels 	


                                      Based on existing HITRAN assignments	

                                                           and 21 transitions	


                          0.20                  Ka=11 levels of 002/130 in HITRAN                                 0.20                    New Ka=11 levels of 002 and 130
                                                    E(Ames-1) - E(Expt), 002                                                                  E(Ames-1) - E(Expt), 002
                                                    E(Ames-1) - E(Expt), 130                                                                  E(Ames-1) - E(Expt), 130
                          0.15                      E(002) - E(130) Expt                                          0.15
                                                                                                                                              E(002) - E(130) Expt




                                                                                         -1
-1




                                                    E(002) - E(130) Ames-1




                                                                                         Energy Difference / cm
Energy Difference / cm




                                                                                                                                              E(002) - E(130) Ames-1
                          0.10                                                                                    0.10


                          0.05                                                                                    0.05


                          0.00                                                                                    0.00


                         -0.05                                                                                    -0.05


                         -0.10                                                                                    -0.10
                                 10        20      30        40        50           60                                    10        20      30        40        50          60
                                                         J                                                                                        J

                         •  9 HITRAN levels and 21 transitions have been relabeled
                         •  2ν3: J=51-57 è ν1+3ν2: J=51-57
                         •  ν1+3ν2: J=51-52 è 2ν3: J=51-52
                                                   SO2 : Line Lists

                                    1E-16
         -1


                                                                             HITRAN2008
          Intensity / cm.molecule
                                    1E-18
                                                                             Ames-296K (J=0-80)
                                    1E-20

                                    1E-22

                                    1E-24

                                    1E-26

                                    1E-28

                                    1E-30
                                            0   1000   2000    3000    4000     5000   6000   7000
                                                         32 16                   -1
                                                           S O2 IR Frequency / cm


•  32S16O2 Line list above. Results for 34S16O2 look very good as well.
•  Clearly, there are a lot of gaps in HITRAN for 32S16O2 (and for 34S16O2, the
   situation is not improved).
•  But there is work to be done…
                                    Comparison to Fitted CDMS:
                                   Purely rotational GS transitions
                                0.10                                             100




                                                                                       Relative Intensity Deviation δ %
     -1




                                                                                 80
     Transition Freq Dev / cm




                                0.05

                                                                                 60

                                0.00
                                                                                 40


                                -0.05                                            20

                                                                                 0
                                -0.10
                                        0   5   10       15       20   25   30
                                                     Ka + J/100
•  Ames-296K vs. CDMS at 300K: 518 transitions from CDMS fitted set
•  Symmetric residual: δ(I)% = 50% * (IAmes/Iobs - Iobs/Iames)
•  Range for Δfreq = -0.0155 – 0.0203 cm-1; for δ(I)% = -4.5% - 10.7%
                                               Comparison to Full CDMS:
                                             Purely rotational GS transitions
                                     0.10                                 100




                                                                                Relative Intensity Deviation δ %
   -1




                                                                          80
    Trnasition Freq Deviation / cm




                                     0.05

                                                                          60

                                     0.00
                                                                          40


                                     -0.05                                20


                                                                          0
                                     -0.10
                                             0    10     20    30    40
                                  Ka + J/100
•  Clearly there are problems with the extrapolated transitions, especially for
   intensities.
•  A new and improved DMS shows the same behavior.
•  We are working to resolve these differences.
                               Accuracy for 32S16O2:
                                  0.01-0.02 cm-1

         Observed (New Expt)	

                                                                                     3ν1	



         Ames-296K Prediction	


3414.0 3413.8 3413.6 3413.4 3413.2 3413.0 3412.8 3412.6 3412.4 3412.2 3412.0




                                             Ames-296K Prediction	


                                                                                                                 ν2 + ν3	


                                                                                     2ν2 + ν3 ß ν2
                                                                                                  	


                                               Observed (New Expt)	


1870.0   1870.2   1870.4    1870.6         1870.8    1871.0   1871.2        1871.4   1871.6   1871.8    1872.0
                           32S16O
                                    2   Transition Frequency / cm-1   	


•  Agreement with experiment is very good (both 2 cm-1 windows)
•  Experiment from: Ulenikov et al. JQSRT 112, 486 (2011).
            Simulation of the Rovibrational
               Spectrum of trans-HOCO




                X. Huang, R. Fortenberry et al.	






•  This is based on purely ab initio calculations.
•  This is a low-resolution simulation.
•  Based on experience, band centers will be off 1-4 cm-1, but the rotational
   pattern/structure should be spot on.
                Conclusions & Future Work
•  State-of-the art for accurate line lists involves a combination of ab initio theory
   and high-resolution laboratory experiment.
•  For NH3, < 0.03 cm-1 errors for rovibrational transitions (up to 5300 cm-1); for
   J=0-6 levels the RMS error only 0.015 cm-1 (HSL-2; HSL-3 coming soon)!
•  Overall RMS error of 0.0156 cm-1 for 6873 rovibrational energy levels of 12C16O2
   with J up to 117 for the Ames-1 PES.
•  For 32S16O2, the weighted σRMS is 0.023 cm-1 (in preparation); more to come.
•  Molecules with large amplitude motions, such as NH3, can be used by astronomers
   to characterize the environment è accurate line lists needed.
•  It is essential to use quality control in determining which experimental data is
   reliable and thus can be used in the refinement step. (energy levels obtained from
   spectroscopic models should be excluded in the refinement procedure)
•  Determining high-quality molecular rovibrational line lists an iterative procedure.
•  DMSs need to be evaluated with their own (larger) grid of points.
•  Similar work on purely ab initio limited line lists for “flowers” is beginning.
                  Acknowledgements
                                        Collaborations with many
                                        experimentalists and
                                        modelers, are gratefully
                                        acknowledged, particularly
                                        K. Sung, L. Brown, H.
                                        Müller, R. Freedman, and
                                        M. Marley.	




Funding from the following programs is gratefully acknowledged:
 •  Laboratory Astrophysics Consortium (NASA; APRA)
 •  Astrophysics Research and Analysis (NASA; APRA)
 •  Venus Express Participating Scientists (NASA)
See Poster by Xinchuan Huang with more details for CO2 and SO2	



				
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posted:9/28/2013
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