Search

For line intensity: • Systematic investigation on the isotopologue consistency of CO 2 and SO 2 IR/MW intensity. • Interesting TDM/Einstein-A patterns found for CO 2 vibrational polyads, SO 2 and CO 2 MW, fundamentals, hotbands, etc. For line positions: • First 2nd-round implementation of BTRHE strategy to minimize the isotope/mass dependent residuals. • –– Two orders of magnitude improvement for SO 2 MW prediction accuracy: 0.01-0.02 MHz (A/B/C), 0-5 MHz (J/Ka<20 lines). • This approach starts from and targets at higher accuracy, can easily extend to other bands or molecules. The semi-empirical molecular rovibrational IR line lists, such as ExoMol, TheoReTs, and Ames, combine the experimental accuracy and theoretical power to reach better than 0.1 cm−1 accuracy for line positions and better than 80–90% agreement for line intensities. The quality of these existing semi-empirical IR lists allows further improvements of intensity and line positions for those unobserved minor isotopologues. This paper presents our new BTRHE (Best Theory + Reliable High-resolution Experiment) strategy implementation. For line intensity, the isotopologue consistency and the patterns of mass dependence in the Ames-296 K SO 2 and CO 2 IR lists are quantitatively presented along the mass-inverse coordinates. The consistency and patterns are better than those in existing experimental data. The methodology proposed here can be used to identify inconsistencies, outliers, and mistakes in intensities, and help improve Effective Dipole Model (EDM) and molecular IR databases. We call for an experimental study on the 50006 and 60007 bands of CO 2 628. For line position predictions, a simple approach combining the variational IR line lists with Effective Hamiltonian (EH) model may refine the effective rotational constants A 0 /B 0 /C 0 and quartic centrifugal distortion constants of minor isotopologues. The prediction accuracy may be improved by two orders of magnitude, i.e. reaching 0–5 MHz prediction accuracy in the range of J < 20–30, K a < 10–20, and 0.01–0.02 MHz accuracy for A 0 /B 0 /C 0. Several important factors have been systematically investigated and discussed, e.g. convergence, uncertainties, higher order terms, fixing EH parameters, mass coordinates, etc. A microwave (MW) line set consisting of 644,636 strong transitions (at 296K) for all 30 isotopologues and corresponding refined EH(Ames) parameters are reported in the supplementary material. This approach may be easily extended to rovibrational bands, hot bands, and other molecular systems. [ABSTRACT FROM AUTHOR]

Highlights • First quantitative validation for the dipole moment surface adopted in Ames-296K SO 2 IR intensity calculations, which integrates variational line lists and effective Hamiltonian and effective dipole model approaches. • Systematic check on the reliability and convergence of vibrational dependence of effective dipole of 13 SO 2 vibrational states. Partition Sum convergence check at 296 K along J and E'. • Isotopologue consistency is superior relative to regular effective dipole models. • Combine the high quality Ames IR intensity with the reliable high-resolution experimental line positions or rovibrational energy levels. • Provide three sets of IR lists for 5 SO 2 isotopologues, the best available alternative for SO 2 high-resolution IR database updates Abstract The quality of Ames-296K SO 2 Infrared (IR) line list intensities is first validated by quantitative exploration of several dipole moment surfaces (DMSs) and partition sum convergence. The DMSs are computed with several of Dunning's correlation-consistent basis sets and their vibrational dependence are compared to the empirical model derived from Stark effect experiments reported by D. Patel, D. Margolese, and T.R. Dyke [ J. Chem. Phys. 70 , 2740 (1979)]. The effective dipole deviations from the DMS adopted in the Ames IR lists is 0.2–0.4% for vibrational states up to 3ν 3. The vibrational dependence of the dipole moment is also in good agreement, except for n ν 1. Partition sum convergence at 296 K is confirmed by new calculations with rotational quantum number J up to 150 and upper state E' up to 8000 cm−1. The isotopologue consistency of the Ames IR line lists is superior relative to the regular Effective Hamiltonian (EH) models and Effective Dipole Moment (EDM) models. The ν 1 + ν 2 and ν 2 + ν 3 intensity consistency check reveals the recently reported experimental intensities need significant improvement or re-analysis. After the accuracy, convergence, and isotopologue consistency have been confirmed, the theoretical Ames-296K intensities are combined with the experimental line positions or EH models that experimental spectroscopists published after 2009. Three high-resolution IR line sets are reported for the 32/33/34S16O 2 , 32S18O 2 and 16O32S18O isotopologues: (1) the "New Lines Sets" include experimentally measured line positions; (2) the "Expanded Line Sets" include possible transitions among new rovibrational levels assigned in experiments and ground state (GS) levels predicted by reliable EH models; (3) the "Ames + MARVEL Sets" include possible transitions among all those levels reported in a recent MARVEL analysis. [Tóbiás et al , JQSRT 208 , 152 (2018)]. Compared to the limited data in High-resolution TRANsmission molecular absorption database (HITRAN), these line sets have significantly improved the data coverage up to 4000 cm−1. Some missing bands can be traced to the unpublished experimental data. The isotopologue consistency of these line sets will help identify the uncertainties and defects in the experimental EH and EDM models. These line sets are good candidates for the next HITRAN update, if line shape parameters are available. The line sets can be downloaded from supplementary files or from the Ames Molecular Spectroscopic Database at http://huang.seti.org. [ABSTRACT FROM AUTHOR]

A new 626-based Ames-2 PES refinement and Ames-2016 line lists for 13 CO 2 isotopologues are reported. A consistent σ RMS = ±0.02 cm −1 is established for hundreds of isotopologue band origins using the Ames-2 PES. Ames-2016 line lists are computed at 296 K, 1000 K and 4000 K using the Ames-2 PES and the same DMS-N2 dipole surface used previously, with J up to 150, E ′ up to 24,000 cm −1 or 18,000 cm −1 and appropriate intensity cutoffs. The lists are compared to the CDSD-296, CDSD-4000 databases, UCL line lists, and a few recent highly accurate CO 2 intensity measurements. Both agreements and discrepancies are discussed. Compared to the old Ames CO 2 lists, the Ames-2016 line lists have line position deviations reduced by 50% or more, which consequently leads to more reliable intensities. The line shape parameters in the Ames-2016 line lists are predicted using the newly assigned conventional vibrational polyad quantum numbers for rovibrational levels below 12,000 cm −1 so the quality of the line shape parameters is similar to that of CDSD or HITRAN. This study further proves that a semi-empirically refined PES (Ames-1 and Ames-2) coupled with a high quality ab initio DMS (DMS-N2 and UCL) may generate IR predictions with consistent accuracy and is thus helpful in the analysis of laboratory spectra and simulations of various isotopologues. The Ames-2016 lists based on DMS-N2 have reached the ∼1% intensity prediction accuracy level for the recent 626 30013-00001 and 20013-00001 bands, but further quantification and improvements require sub-percent or sub-half-percent accurate experimental intensities. The inter-isotopologue consistency of the intensity prediction accuracies should have reached better than 1–3% for regular bands not affected by resonances. Since the Effective Dipole Models (EDM) in CDSD and HITRAN have 1–20% or even larger uncertainties, we show that the Ames lists can provide better alternative IR data for many hard-to-determine isotopologue bands. Comparison at 4000 K suggests that the Ames-4000 K 12 C 16 O 2 line list is reliable and consistent within the current cutoffs of J  ≤ 150 and E ′ ≤ 24,000 cm −1 , but intensity contributions involving higher energy levels should not be omitted and future computations need to be converged up to at least 32,000 cm −1 or higher. The remaining issues are discussed regarding the source of energy level discrepancies, intensity underestimations by ∼50% for some weak bands, etc. and also future work. [ABSTRACT FROM AUTHOR]

We have carried out extensive ab initio calculations of the electronic structure of methane, and these results are used to compute vibrational energy levels. We include basis set extrapolations, core–valence correlation, relativistic effects, and Born–Oppenheimer breakdown terms in our calculations. Our ab initio predictions of the lowest lying levels are superb. [ABSTRACT FROM AUTHOR]

Total internal partition sums (TIPS) are reported for 166 isotopologues of 51 molecules important in planetary atmospheres. Molecules 1 to 50 are taken from the HITRAN2016 list, and, in some cases, additional isotopologues are considered for some of the molecules. Molecules 51–53 are C 3 H 4 , CH 3 , and CS 2 , respectively. TIPS are not reported for the O atom and CF 4 ; thus, while there are 53 species in the list, data are reported for 51 molecules. The TIPS are determined by various methods from 1 K to a T max that ensures the TIPS reported have converged. These data are provided with HITRAN2016 and a new version of the TIPS code is available in both FORTRAN and python languages. [ABSTRACT FROM AUTHOR]

Reliable infrared (IR) line lists are reported for the 13 isotopologues of carbon dioxide in HITRAN notation: 626, 636, 628, 627, 828, 727, 827, 638, 637, 737, 838, 738, and 646. Three IR lists are available for each istotopologue: a complete list at 296K, a reduced-size list at 296K, plus a reduced-size list at 1000K. They are denoted Ames-296K, Ames-296K.reduced and Ames-1000K.reduced. With J up to 150, and energy up to 18,000cm−1 above the zero point energy, these lists are expected to cover the temperature range up to 1500K. Line shape parameters including temperature dependence are calculated and reported for four temperature ranges: Mars, Earth, Venus, and Hotter (700-2000K). Comparisons are made against the available transition data in the HITRAN2012 models. Line position accuracy for most transitions up to 10,000-13,000cm−1 is better than 0.03-0.05cm−1. Computed transition intensities agree well with most HITRAN data but there exist suspicious exceptions for isotopologues. These line lists will expedite CO2 IR experimental data analysis and provide the scientific community with trustworthy alternatives for unknown IR bands. These line lists may be combined with existing experimental databases to facilitate the analysis of future laboratory experiments or astronomical observations. [ABSTRACT FROM AUTHOR]

Abstract: New semi-empirical Infrared (IR) line lists for 12C16O2, Ames-296K and Ames-1000K, have been computed using a newly updated ab initio CCSD(T)/aug-cc-pVQZ dipole moment surface (denoted DMS-N2) and an empirically refined potential energy surface (Ames-1). J=0–150 rovibrational levels are computed up to 30,000cm−1, and related transitions are cut off at 1E−42cmmolecule−1 (296K) and 1E−36cmmolecule−1 (1000K). These are the first line lists available to cover reliably the energy region as high as ~20,000cm−1. Recent experimental data at 1.1μm has confirmed the predicted intensities for the 50013-00001 and 50014-00001 band transitions have better than 90% agreement. Comparisons are made against the Wattson 750K line list and HITEMP/HITRAN at 300K, 500K, 725K, 1000K, 1500K, 2000K and 3000K. The temperature dependence and accuracy of the new Ames-296K/1000K line lists are investigated and we claim both line lists are capable of providing reliable opacities up to 18,000–23,000cm−1, while the highest applicable wavenumber range drops as T rises. We suggest caution is used for T>1000K simulations. Comparison to recent experiments at 1000K, 1550K and 1773K shows that the Ames-1000K line list and HITEMP perform similarly in the 3200–3800cm−1 and 4600–5200cm−1 ranges. In the 2000–2100cm−1 range, Ames-1000K yields better agreement relative to experiment. Existing problems and possible future solutions in the new Ames-296K/1000K line lists for line positions and intensities are also discussed. [Copyright &y& Elsevier]

• Laboratory measurement and theoretical analysis for 14NH 3 IR spectra in 5600–6300 cm−1. • Assigned definitive rovibrational quantum numbers to 1602 transitions pertaining to 809 upper levels and eight vibrational bands. Good for h eff models. • The JPL+Ames (JA) line list reports 87 new lines and 179 new assignments. Other assignments agree with Cacciani et al. for 1278 transitions. • Band-by-band quality check uses the δΕ and δΔ consistency analysis. The Ames HSL-Pre3 line positions are still more accurate than C2018 for this range. • The JA lists of 14NH 3 transitions and levels are reported in supplementary files. We report new results from combined efforts of laboratory measurements and theoretical analysis for 14NH 3 in the 5600–6300 cm−1 region, based on Kitt Peak spectra previously used in the study of the 6300–7000 cm−1 region [Sung et al., JQSRT 2012, 113:1066]. Definitive rovibrational quantum numbers were assigned for 1602 transitions pertaining to 809 upper levels and eight vibrational bands: 0111 E , 0111 A , 1101, 0310, 0211, 1300, 0103 and 0302. When compared to the results from Cacciani et al. [JQSRT 2020, 258:107,334], our results, termed as the "JPL+Ames 2021" list (or JA list), showed good agreement for the assignment of 1278 transitions. We have further made new assignments for 179 transitions that were not assigned in their work, plus assignments for 87 new lines reported for the first time. Excellent agreement (± 0.002 cm−1) was observed in the line positions between this work and Cacciani et al., with no systematic discrepancies. Remaining discrepancies on the assignments have been attributed to line blendings, unaccounted resonances, the uncertainties of reference line lists, and limited transition-matching accuracy. An empirical line list (JPL) and a semi-empirical line list adopting the UCL-C2018 [Coles et al., JQSRT 2018, 219:199] intensity with the Ames HSL-Pre3 based line positions were employed as the major reference for our analysis. In addition to the line position / intensity measurements and cross-validation through combination difference analysis, part of the work has also required manual matches for valid transition and level pairs and checking the consistency and patterns of δΕ Calc-Obs , inversion splittings Δ a-s , etc. Band-by-band discussions are presented on the missing intensity of ν 2 +3ν 4 (0103), the unusual sensitivity of ν 1 +3ν 2 (1300) s levels, the borrowed intensity of 6ν 2 (0600), and potential outliers of ν 1 +ν 2 +ν 4 (1101), etc. These will be the topics in our future work. [ABSTRACT FROM AUTHOR]

Abstract: Nearly 4800 features of ammonia between 6300 and 7000cm−1 with intensities ≥4×10−24 cm−1/(molecule·cm−2) at 296K were measured using 16 pure NH3 spectra recorded at various temperatures (296–185K) with the McMath–Pierce Fourier Transform Spectrometer at Kitt Peak National Observatory, AZ. The line positions and intensities were retrieved by fitting individual spectra based on a Voigt line shape profile and then averaging the values to form the experimental linelist. The integrated intensity of the region was 4.68×10−19 cm−1/(molecule·cm−2) at 296K. Empirical lower state energies were also estimated for 3567 absorption line features using line intensities retrieved from 10 spectra recorded at gas temperature between 185 and 233K. Finally, using Ground State Combination Differences (GSCDs) and the empirical lower state energy estimates, the quantum assignments were determined for 1096 transitions in the room temperature linelist, along with empirical upper state energies for 434 levels. The assignments correspond to seven vibrational states, as confirmed from recent ab initio calculations. The resulting composite database of 14NH3 line parameters will provide experimental constraints to ab initio calculations and support remote sensing of gaseous bodies including the atmospheres of Earth, (exo)planets, brown dwarfs, and other astrophysical environments. [Copyright &y& Elsevier]

Rich reactive resonances are found in a 3D quantum dynamics study of the N + N2 exchange reaction using our recently developed ab initio potential energy surface that has a shallow well between two transition states. An L2 analysis confirms that the quasibound states of ‘Lake Eyring’ are responsible for the reactive resonances with some quasibound states, mostly the bending motions, giving rise to strong reasonance peaks, whereas others contributing to the shoulders in the resonance structure. This is the first observation of reactive resonances from a ‘Lake Eyring’ feature in a potential energy surface. [Copyright &y& Elsevier]