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To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt 'Best Theory + Reliable High-resolution Experiment' (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The 'Ames-1' potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σrms = 0.02–0.03 cm-1 for five isotopologues. The 'Ames-1' dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (SAmes) are demonstrated through comparisons with HITRAN (SHITRAN), NOSL-296 (SNOSL), recent observed intensities (Sobs) and Effective Dipole Model (EDM) intensities (SEDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for SAmes. The SAmes provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at and https://doi.org/10.48667/9kmk-0334. [ABSTRACT FROM AUTHOR]

A purely ab initio potential energy surface (PES) was refined with selected 32S16O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (σRMS) for all J = 0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm-1. Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296 K and covers up to 8000 cm-1. Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85%- 90%. Our predictions for 34S16O2 band origins, higher energy 32S16O2 band origins and missing 32S16O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict 32/34S16O2 band origins below 5500 cm-1 with 0.01-0.03 cm-1 uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The Ka-dependence of both line position and line intensity errors is discussed. The line list will greatly facilitate SO2 IR spectral experimental analysis, as well as elimination of SO2 lines in high-resolution astronomical observations. [ABSTRACT FROM AUTHOR]

An isotopic-independent, highly accurate potential energy surface (PES) has been determined for CO2 by refining a purely ab initio PES with selected, purely experimentally determined rovibrational energy levels. The purely ab initio PES is denoted Ames-0, while the refined PES is denoted Ames-1. Detailed tests are performed to demonstrate the spectroscopic accuracy of the Ames-1 PES. It is shown that Ames-1 yields σrms (root-mean-squares error) = 0.0156 cm-1 for 6873 J = 0-117 12C16O2 experimental energy levels, even though less than 500 12C16O2 energy levels were included in the refinement procedure. It is also demonstrated that, without any additional refinement, Ames-1 yields very good agreement for isotopologues. Specifically, for the 12C16O2 and 13C16O2 isotopologues, spectroscopic constants Gv computed from Ames-1 are within ±0.01 and 0.02 cm-1 of reliable experimentally derived values, while for the 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 12C18O2, 17O12C18O, 12C17O2, 13C18O2, 13C17O2, 17O13C18O, and 14C16O2 isotopologues, the differences are between ±0.10 and 0.15 cm-1. To our knowledge, this is the first time a polyatomic PES has been refined using such high J values, and this has led to new challenges in the refinement procedure. An initial high quality, purely ab initio dipole moment surface (DMS) is constructed and used to generate a 296 K line list. For most bands, experimental IR intensities are well reproduced for 12C16O2 using Ames-1 and the DMS. For more than 80% of the bands, the experimental intensities are reproduced with σrms(ΔI) < 20% or σrms(ΔI/δobs) < 5. A few exceptions are analyzed and discussed. Directions for future improvements are discussed, though it is concluded that the current Ames-1 and the DMS should be useful in analyzing and assigning high-resolution laboratory or astronomical spectra. [ABSTRACT FROM AUTHOR]

A global potential energy surface (PES) that includes short and long range terms has been determined for the NH3 molecule. The singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations and the internally contracted averaged coupled-pair functional electronic structure methods have been used in conjunction with very large correlation-consistent basis sets, including diffuse functions. Extrapolation to the one-particle basis set limit was performed and core correlation and scalar relativistic contributions were included directly, while the diagonal Born–Oppenheimer correction was added. Our best purely ab initio PES, denoted “mixed,” is constructed from two PESs which differ in whether the ic-ACPF higher-order correlation correction was added or not. Rovibrational transition energies computed from the mixed PES agree well with experiment and the best previous theoretical studies, but most importantly the quality does not deteriorate even up to 10 300 cm-1 above the zero-point energy (ZPE). The mixed PES was improved further by empirical refinement using the most reliable J=0–2 rovibrational transitions in the HITRAN 2004 database. Agreement between high-resolution experiment and rovibrational transition energies computed from our refined PES for J=0–6 is excellent. Indeed, the root mean square (rms) error for 13 HITRAN 2004 bands for J=0–2 is 0.023 cm-1 and that for each band is always ≤=0.06 cm-1. For J=3–5 the rms error is always ≤=0.15 cm-1. This agreement means that transition energies computed with our refined PES should be useful in the assignment of new high-resolution NH3 spectra and in correcting mistakes in previous assignments. Ideas for further improvements to our refined PES and for extension to other isotopolog are discussed. [ABSTRACT FROM AUTHOR]

Highlights • Spectroscopic data for the remote sensing of :CNH 2 + and :CCH 2 in Titans atmosphere are provided. • :CNH 2 + has the same m/z = 28 value as the HCNH + ion believed to have been sampled by Cassinis INMS. • :CNH 2 + has a large (2.2 D) dipole moment and a bright infrared feature at 5.8 µm. Abstract The highest peak in Cassini 's INMS data for stratospheric flybys of Titan's atmosphere is m / z = 28. While this has mostly been attributed to HCNH + , minor contributions from N 2 + and C 2 H 2 + are also likely. However, this work shows that :CNH 2 + may also be present in a kinetically-favorable potential well based on high-level quantum chemical computations. The ionization energy of N 2 is much higher than the isomerization barrier between HCNH + and :CNH 2 +. As such, we present computations that provide vibrational and rotational spectroscopic data for the possible remote sensing of this molecule in Titan's atmosphere. Such data are also computed for the isoelectronic :CCH 2 molecule, and comparison to previous laboratory experiments and quantum chemical computations, where available for the hydrocarbon, is excellent. Consequently, the data provided in this work should allow for initial searches for :CNH 2 + as well as refinements of data for :CCH 2 both in the laboratory and even in Titan's atmosphere. [ABSTRACT FROM AUTHOR]

The equilibrium structures, dipole moments, harmonic vibrational frequencies, and infrared intensities of NH3, FON, Be3, BeC2, and BeO2 have been determined using the coupled-cluster and Brueckner electron correlation methods. The singles and doubles coupled-cluster (CCSD) and the Brueckner doubles (BD) methods have been employed and the corresponding methods that include a perturbational estimate of connected triple excitations [i.e., CCSD(T) and BD(T)] have also been investigated. The T1 diagnostic [Int. J. Quantum Chem. Symp. 23, 199 (1989)] is found to provide a good indication of the magnitude of the difference between the results obtained with the coupled-cluster and Brueckner methods. For NH3, the T1 diagnostic is small and so the differences between results obtained from coupled-cluster and Brueckner theories are quite small. For the other four molecules the T1 diagnostic is larger, and so the differences between the coupled-cluster and Brueckner methods become larger. However, it is found for all of the molecules considered in this study that inclusion of the contribution from connected triple excitations is more important than the differences between the Brueckner and coupled-cluster correlation methods. [ABSTRACT FROM AUTHOR]

The importance of including triple and quadruple excitations (relative to a single Hartree–Fock determinant) in ab initio electronic structure configuration interaction (CI) theory is investigated for several small molecules [HF, N2, CO, H2O, NH3, (3B1) CH2, and (1A1) CH2]. Specifically the effects of these high order electron correlations on equilibrium molecular geometries, dipole moments, harmonic vibrational frequencies, and infrared intensities are reported. Triple and quadruple excitations are generally found to affect the dipole moment, in an absolute sense, only slightly. In some cases, infrared intensities show a medium to large dependence on higher excitations. Molecular geometries, and subsequently the harmonic vibrational frequencies, however, are significantly more dependent upon these higher excitations. Quadruple excitations are found to be significantly more important than triple excitations for all closed shell systems except for CO, where the relative importance of triples to quadruples is roughly 2:3 in predicting for vibrational frequencies. On the other hand, it is found that triples and quadruples are of nearly equal importance for 3B1 CH2. The equilibrium bond length and molecular properties of the multiply bonded species CO and N2 show a larger absolute dependence on the higher than double excitations. Several additional levels of theory [e.g., all singles, doubles, and quadruples (CISDQ)] have been applied to HF and N2 in a more detailed investigation of the structure of the CI Hamiltonian matrix. It is concluded that only a very small subset of the triply and quadruply excited configurations account for nearly all of the higher excitation effects on harmonic frequencies. [ABSTRACT FROM AUTHOR]

Examines the equilibrium dipole moment, harmonic vibrational frequencies and infrared intensities of bromine nitrate. Importance of the reaction of ozone with halogen compounds; Implications for the ozone layer depletion; Inquiry on the gas-phase vibrational spectrum of bromine nitrate.

The title molecular anions have been studied at the self-consistent-field (SCF) level of theory with several different basis sets. The smallest of these bases is triple zeta (TZ) in quality while the largest can be labeled near Hartree–Fock limit. The dependence of proton affinities, dipole moments, harmonic frequencies, and infrared intensities on the inclusion of diffuse functions in the basis set is investigated. It is concluded that at the SCF level of theory the addition of diffuse s and p functions (for first row elements) is necessary in order to obtain reliable results. This is true especially for NH-2 and CH-3. A method to extend any standard Gaussian basis set is suggested. Finally, predictions are made for some of the as yet unobserved fundamentals of the anions. [ABSTRACT FROM AUTHOR]

Sulphur dioxide is well-known in the atmospheres of planets and satellites, where its presence is often associated with volcanism, and in circumstellar envelopes of young and evolved stars as well as the interstellar medium. This work presents a line list of 1.3 billion 32S16O2 vibration-rotation transitions computed using an empirically adjusted potential energy surface and an ab initio dipole moment surface. The list gives complete coverage up to 8000 cm-1 (wavelengths longer than 1.25 µm) for temperatures below 2000 K. Infrared absorption crosssections are recorded at 300 and 500 C are used to validated the resulting ExoAmes line list. The line list is made available in electronic form as supplementary data to this article and at www.exomol.com. [ABSTRACT FROM AUTHOR]

The equilibrium structure, dipole moment, harmonic vibrational frequencies, and infrared intensities of XONO[sub 2] (X=Br, OBr, O[sub 2]Br) are determined using density functional theory in conjunction with a TZ2P (triple zeta double polarized) basis set. The B3LYP functional was used since this has previously been shown to perform well for similar bromine compounds. The equilibrium geometry and vibrational spectra of BrONO[sub 2] are shown to be in good agreement with the experimental data and also with high-level coupled-cluster calculations. The vibrational spectrum of O[sub 2]BrONO[sub 2] has been compared with that of the chlorine analog, O[sub 2]ClONO[sub 2], for which some experimental data exist. The bonding in OBrONO[sub 2] is shown to be more similar to that in BrONO[sub 2]. Using large atomic natural orbital basis sets, the singles and doubles coupled-cluster method that includes a perturbative correction for triple excitations, denoted CCSD(T), was employed to compute energies for three isodesmic reactions in order to determine heats of formation for OBrONO[sub 2] and O[sub 2]BrONO[sub 2]. Our best estimates are 36.7 and 38.7 kcal/mol, respectively. Finally, the possible formation of O[sub 2]BrONO[sub 2] in the stratosphere by adduct formation and oxidation of OBrONO[sub 2] and the implications for stratospheric bromine chemistry are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A purely ab initio potential energy surface (PES) was refined with selected 32S16O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (σRMS) for all J = 0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm-1. Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296 K and covers up to 8000 cm-1. Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85%- 90%. Our predictions for 34S16O2 band origins, higher energy 32S16O2 band origins and missing 32S16O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict 32/34S16O2 band origins below 5500 cm-1 with 0.01-0.03 cm-1 uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The Ka-dependence of both line position and line intensity errors is discussed. The line list will greatly facilitate SO2 IR spectral experimental analysis, as well as elimination of SO2 lines in high-resolution astronomical observations. [ABSTRACT FROM AUTHOR]

A global potential energy surface (PES) that includes short and long range terms has been determined for the NH3 molecule. The singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations and the internally contracted averaged coupled-pair functional electronic structure methods have been used in conjunction with very large correlation-consistent basis sets, including diffuse functions. Extrapolation to the one-particle basis set limit was performed and core correlation and scalar relativistic contributions were included directly, while the diagonal Born–Oppenheimer correction was added. Our best purely ab initio PES, denoted “mixed,” is constructed from two PESs which differ in whether the ic-ACPF higher-order correlation correction was added or not. Rovibrational transition energies computed from the mixed PES agree well with experiment and the best previous theoretical studies, but most importantly the quality does not deteriorate even up to 10 300 cm-1 above the zero-point energy (ZPE). The mixed PES was improved further by empirical refinement using the most reliable J=0–2 rovibrational transitions in the HITRAN 2004 database. Agreement between high-resolution experiment and rovibrational transition energies computed from our refined PES for J=0–6 is excellent. Indeed, the root mean square (rms) error for 13 HITRAN 2004 bands for J=0–2 is 0.023 cm-1 and that for each band is always ≤=0.06 cm-1. For J=3–5 the rms error is always ≤=0.15 cm-1. This agreement means that transition energies computed with our refined PES should be useful in the assignment of new high-resolution NH3 spectra and in correcting mistakes in previous assignments. Ideas for further improvements to our refined PES and for extension to other isotopolog are discussed. [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]

The azirinyl cation (C2H2N+) and its geometrical isomers could be present in the interstellar medium. The C2H2N+ isomers are, however, difficult to identify in interstellar chemistry because of the lack of high-resolution spectroscopic data from laboratory experiments. Ab initio quantum chemical methods were used to characterize the structures, relative energies, and spectroscopic and physical properties of the low energy isomers of the azirinyl cation. We have employed second-order Møller-Plesset perturbation theory (MP2), second-order Z-averaged perturbation theory (ZAPT2), and coupled cluster theory with singles and doubles with perturbative triples CCSD(T) methods along with large correlation consistent basis sets such as cc-pVTZ, cc-pCVTZ, cc-pVQZ, cc-pCVQZ, and cc-pV5Z. Harmonic vibrational frequencies, dipole moments, rotational constants, and proton affinities for the lowest energy isomers were calculated using the CCSD(T) method. Azirinyl cation, a cyclic isomer, is lowest in energy at all levels of theory employed. Azirinyl cation is followed by the cyanomethyl cation (H2CCN)+, isocyanomethyl cation (H2CNC)+, and a quasilinear HCCNH+ cation, which are 13.8, 17.3, and 21.5 kcal mol-1 above the cyclic isomer, respectively, at the CCSD(T)/cc-pV5Z level of theory. The lowest three isomers all have C2v symmetry and ¹A1 ground electronic states. The quasilinear HCCNH+ cation has a Cs symmetry planar structure, and a ³A" electronic ground state, unlike what some previous work suggested. [ABSTRACT FROM AUTHOR]

Using the latest published, empirically refined potential energy surface (PES) Ames-1 and purely ab initio CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), we have computed infrared line lists for five symmetric isotopologues of sulfur dioxide: 32 S 16 O 2 (626), 33 S 16 O 2 (636), 34 S 16 O 2 (646), 36 S 16 O 2 (666), and 32 S 18 O 2 (828). The line lists are based on J = 0–80 rovibrational variational calculations with E ′ ⩽ 8000 cm −1 . The 34 S 16 O 2 and 33 S 16 O 2 line lists are compared to the experiment-based models in the HIgh-resolution TRANsmission molecular absorption database (HITRAN2012, http://www.cfa.harvard.edu/hitran/ ) and the Cologne Database for Molecular Spectroscopy, CDMS ( http://www.astro.uni-koeln.de/cdms/ ). The accuracy for computed 646 band origins is similar to what has been reported for the main isotopologue, i.e. 0.01–0.03 cm −1 for bands up to 5500 cm −1 . For rovibrational transitions, the 646 line position and intensity deviation patterns are much simpler and more self-consistent than those of the main isotopologue 626. The discrepancies are mainly found for higher K a / J transitions. 626 and 646 exhibit comparable line position and intensity agreement for lower K a / J transitions. The line position deviations for the 636 purely rotational band are parallel to those of 626 and 646, while its line intensity deviations do not show branching patterns as we found in the 626 and 646 cases. Predictions for the other minor isotopologues are expected to exhibit similar accuracy. These line lists are accurate enough to provide alternatives for missing bands of 626 and the minor isotopologues. It may significantly facilitate the laboratory spectroscopic measurement and analysis, as well as to identify these isotopologues in various astrophysical environments. [ABSTRACT FROM AUTHOR]

• The next most likely isomer of H 2 CS present in the ISM is trans-HCSH. • Even so, the cis-HCSH isomer may be the most likely to be observed. • H 2 SC is more observable but is likely too high in energy to be observed.. The missing sulfur of the interstellar medium may be hiding in molecules for which there are no spectral data yet available for any astrophysical observation, molecules like isomers of H 2 CS a known interstellar compound. Every known interstellar molecule is a pointer to the presence and detectability of related molecules in the ISM. This quantum chemical study provides the necessary spectral data for the observation of cis -, trans -, and 3 A HCSH as well as for 1 A 1 and 3 A ″ H 2 SC. Benchmarks of the CCSD(T)-F12/cc-pVTZ-F12 quartic force field for the known thioformaldehyde provide anharmonic vibrational frequencies of with an average of 1.9 cm−1 of gas-phase experiment demonstrating reliability for the computed fundamental frequencies. The 1 A 1 H 2 SC form has bright spectral features in the infrared and millimeter-wave regimes, but is the highest-energy species of this set. The trans -HCSH isomer is the lowest-energy (43.69 kcal/mol or 1.90 eV) isomer next to thioformaldehyde, but the slightly higher cis -HCSH isomer has greater intensities for its brightest fundamental frequencies and a larger dipole moment making it potentially more likely to be observed. These data determined here may also assist in laboratory characterization of these molecules and how their chemistry will likely progress. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hot CO 2 IR line list covering 0 – 20,000 cm−1 and up to 3000 K. • CDSD2019-based PES refinement and one of the best CO 2 DMS are adopted. • Using CDSD2019 energy levels (J < 150 and E' < 24,000 cm−1) for more accurate line positions. • Using the more accurate A 21 of Ames-2021 296K IR line list for E ' < 15,000 cm−1 transitions. • Better overall agreement with Shock Tube experiments up to 2000 K, compared to HITEMP and UCL-4000. AI-3000K is a semi-empirical IR line list constructed for hot CO 2 spectra analysis and simulation up to 3000 – 4000 K. Compared to previously published Ames-1000K and UCL-4000, it represents a major upgrade, utilizing a new algorithm for optimization and including the latest improvements in potential energy surface (PES), dipole moment surface (DMS), and room temperature IR line list (Ames-2021 296K). To maximize the success of introducing experimental based accurate line positions, a new PES (X01d) was refined with respect to >800 selected CDSD2019 [Tashkun et al. JQSRT (2019) 228 , 124] energy levels in the range of 0 – 24,000 cm−1, with σ rms = 0.5 – 0.7 cm−1. Most differences between the X01d PES based levels and CDSD2019 energies are within ± 2 cm−1. A new DMS is fitted from extrapolated CCSD(T)/aug-cc-pV(T,Q,5)Z dipole calculations, with σ rms = 5.1 × 10−6 au for 11,155 geometries up to 40,000 cm−1, denoted Ames-2021–40K. Compared to the best available Ames-2021 DMS and room temperature IR line list [Huang et al J. Phys. Chem. A (2022) 126 , 5940], the relative intensity differences are expected to be ∼ 1 ‰. The line position accuracy of ''X01d + Ames-2021–40K'' IR line list is significantly improved by adopting CDSD2019 energy levels up to 24,000 cm−1 (J ≤ 150). The Einstein A 21 coefficients for E ' < 15,000 cm−1 transitions are replaced by more accurate values from the Ames-2021 296K IR line list. In short, the AI-3000K is the X01d PES and Ames-2021–40K DMS based line list enhanced with the A 21 of Ames-2021 296K line list and CDSD energy levels. It provides continuous coverage from 0 to 20,000 cm−1 for the four most abundant isotopologues: 12C16O 2 (6 2 6), 13C16O 2 (6 3 6), 16O12C18O (6 2 8), and 16O12C17O (6 2 7). The impacts of isotopologue and E '/ E '' cutoffs have been examined. Intensity convergence (not accuracy) of AI-3000K line list is quantitatively estimated in 1 cm−1 bins. It is better than 99% in the whole range of 0 – 20,000 (or 10,000) cm−1 at 1000 K (or 2000 K), or better than 90% in the whole range of 0 – 15,000 (or 9000) cm−1 at 2000 K (or 3000 K), respectively. Convergence beyond 3000 K will require a new PES and DMS for E ' > 40,000 cm−1. The AI-3000K and HITEMP based IR simulations are compared to high resolution shock tube experiments for CO 2 -Ar mixture up to 2000 K. With line position accuracy comparable to that of HITEMP, AI-3000K IR line list yields better agreements at more frequencies. Potential sources of discrepancies with experiment are discussed. [ABSTRACT FROM AUTHOR]

Sulphur dioxide is well-known in the atmospheres of planets and satellites, where its presence is often associated with volcanism, and in circumstellar envelopes of young and evolved stars as well as the interstellar medium. This work presents a line list of 1.3 billion 32S16O2 vibration-rotation transitions computed using an empirically adjusted potential energy surface and an ab initio dipole moment surface. The list gives complete coverage up to 8000 cm-1 (wavelengths longer than 1.25 µm) for temperatures below 2000 K. Infrared absorption crosssections are recorded at 300 and 500 C are used to validated the resulting ExoAmes line list. The line list is made available in electronic form as supplementary data to this article and at www.exomol.com. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quartic Force Fields (QFFs) yield highly accurate spectra including rotational structure. [•] Infrared intensities (IR) are well determined using a CCSD(T) Dipole Moment Surface (DMS). [•] Purely ab initio IR intensities agree extremely well with high-resolution experiment. [•] Purely ab initio transition energies agree very well with high-resolution experiment. [•] Ab initio purely rotational and rovibrational line lists should aid astronomers to assign lines. [Copyright &y& Elsevier]

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]

The vibrational spectra for the HOCO radical in bothof its conformersand deuterated isotopologues are shown here for the first time. Buildingon previous work with coupled cluster quartic force fields (QFFs)in the computation of the fundamental vibrational frequencies forboth cis- and trans-HOCO, coupledcluster dipole surfaces are now provided for both HOCO conformersand their corresponding deuterated isotopologues. These surfaces andsubsequent vibrational configuration interaction (VCI) computationsproduce the intensities of transitions into vibrational states includingthe fundamentals, overtones, and first few combination bands of lessthan 4000 cm–1, slightly beyond the O–H stretch.Simulated spectra with an artificial full width at half-maximum broadeningof 10 cm–1are also provided in order to aid inthe characterization of HOCO’s vibrational frequencies andto assist detection in various laboratory or astronomical observations. [ABSTRACT FROM AUTHOR]