Search

A large set of validated experimental transitions and empirical rovibrational energy levels are reported for the fifth most abundant carbon dioxide isotopologue, 16O13C18O (in a shorthand notation, 638). Validation of the transitions and determination of the empirical energy levels are based on a compiled and carefully checked dataset, collected from 35 literature sources, containing 12 348/7432 measured/unique lines in the wavenumber range of 578–9318 cm−1. The MARVEL (Measured Active Rotational‐Vibrational Energy Levels) protocol, built upon the theory of spectroscopic networks, not only validates the vast majority of the measured transitions, but also yields 3975 empirical rovibrational energy levels, with uncertainty estimates compliant with the experimental uncertainties of the transitions. [ABSTRACT FROM AUTHOR]

Empirical rovibrational energy levels are presented for the third most abundant, asymmetric carbon dioxide isotopologue, 16O12C18O, based on a compiled dataset of experimental rovibrational transitions collected from the literature. The 52 literature sources utilized provide 19,438 measured lines with unique assignments in the wavenumber range of 2–12,676 cm−1. The MARVEL (Measured Active Rotational‐Vibrational Energy Levels) protocol, which is built upon the theory of spectroscopic networks, validates the great majority of these transitions and outputs 8786 empirical rovibrational energy levels with an uncertainty estimation based on the experimental uncertainties of the transitions. Issues found in the literature data, such as misassignment of quantum numbers, typographical errors, and misidentifications, are fixed before including them in the final MARVEL dataset and analysis. Comparison of the empirical energy‐level data of this study with those in the line lists CDSD‐2019 and Ames‐2021 shows good overall agreement, significantly better for CDSD‐2019; some issues raised by these comparisons are discussed. [ABSTRACT FROM AUTHOR]

A model based on the finite-basis representation of a vibrational Hamiltonian expressed in internal coordinates is developed. The model relies on a many-mode, low-order expansion of both the kinetic energy operator and the potential energy surface (PES). Polyad truncations and energy ceilings are used to control the size of the vibrational basis to facilitate accurate computations of the OH stretch and HOH bend intramolecular transitions of the water dimer ( H 2 16 O)2. Advantages and potential pitfalls of the applied approximations are highlighted. The importance of choices related to the treatment of the kinetic energy operator in reduced-dimensional calculations and the accuracy of different water dimer PESs are discussed. A range of different reduced-dimensional computations are performed to investigate the wavenumber shifts in the intramolecular transitions caused by the coupling between the intra- and intermolecular modes. With the use of symmetry, full 12-dimensional vibrational energy levels of the water dimer are calculated, predicting accurately the experimentally observed intramolecular fundamentals. It is found that one can also predict accurate intramolecular transition wavenumbers for the water dimer by combining a set of computationally inexpensive reduced-dimensional calculations, thereby guiding future effective-Hamiltonian treatments. [ABSTRACT FROM AUTHOR]

Network theory has fundamentally transformed our comprehension of complex systems, catalyzing significant advances across various domains of science and technology. In spectroscopic networks, hubs are the quantum states involved in the largest number of transitions. Here, utilizing network paths probed via precision metrology, absolute energies have been deduced, with at least 10-digit accuracy, for almost 200 hubs in the experimental spectroscopic networks of H216O and H218O. These hubs, lying on the ground vibrational states of both species and the bending fundamental of H216O, are involved in tens of thousands of observed transitions. Relying on the same hubs and other states, benchmark-quality line lists have been assembled, which supersede and improve, by three orders of magnitude, the accuracy of the massive amount of data reported in hundreds of papers dealing with Doppler-limited spectroscopy. Due to the omnipresence of water, these ultraprecise line lists could be applied to calibrate high-resolution spectra and serve ongoing and upcoming space missions. Ultraprecise spectral line lists of molecules such as water, omnipresent in various environments, can be used to calibrate high-resolution spectra, which is particularly relevant for exoplanet transit observations. Here, the authors use measured spectra and network theory to achieve ultraprecise characterization of H216O and H218O hubs, the most relevant quantum states within a spectroscopic network. [ABSTRACT FROM AUTHOR]

Lamb dips of twenty lines in the P, Q, and R branches of the ν1 + ν3 + ν41 vibrational band of 12C2H2, in the spectral window of 7125–7230 cm−1, have been measured using an upgraded comb-calibrated frequency-stabilized cavity ring-down spectrometer, designed for extensive sub-Doppler measurements. Due to the large number of carefully executed Lamb-dip experiments, and to the extrapolation of absolute frequencies to zero pressure in each case, the combined average uncertainty of the measured line-center positions is 15 kHz (5 × 10−7 cm−1) with a 2-σ confidence level. Selection of the twenty lines was based on the theory of spectroscopic networks (SN), ensuring that a large number of transitions, measured previously by precision-spectroscopy investigations, could be connected to the para and ortho principal components of the SN of 12C2H2. The assembled SN contains 331 highly precise transitions, 119 and 121 of which are in the ortho and para principal components, respectively, while the rest remain in floating components. The para- and ortho-12C2H2 energy-level lists, determined during the present study, contain 82 and 80 entries, respectively, with an accuracy similar to that of the lines. Based on the newly assembled lists of para- and ortho-12C2H2 empirical energy levels, a line list, called TenkHz, has been generated. The TenkHz line list contains 282 entries in the spectral range of 5898.97–7258.87 cm−1; thus far, only 149 of them have been measured directly via precision spectroscopy. The TenkHz line list includes 35 intense lines that are missing in the HITRAN2020 database. [ABSTRACT FROM AUTHOR]

Detailed understanding of the energy-level structure of the quantum states as well as of the rovibronic spectra of the ethylidyne (CH) and the hydroxyl (OH) radicals is mandatory for a multitude of modelling efforts within multiple chemical, combustion, astrophysical, and atmospheric environments. Accurate empirical rovibronic energy levels, with associated uncertainties, are reported for the low-lying doublet electronic states of 12CH and 16OH, using the Measured Active Rotational-Vibrational Energy Levels (M ARVEL) algorithm. For 12CH, a total of 1521 empirical energy levels are determined in the primary spectroscopic network (SN) of the radical, corresponding to the following seven electronic states: X 2Π, A 2Δ, B 2Σ−, C2 Σ+, D 2Π, E 2Σ+, and F 2Σ+. The energy levels are derived from 6348 experimentally measured and validated transitions, collected from 29 sources. For 16OH, the lowest four doublet electronic states, X 2Π, A 2Σ+, B 2Σ+, and C 2Σ+, are considered, and a careful analysis and validation of 15 938 rovibronic transitions, collected from 45 sources, results in 1624 empirical rovibronic energy levels. The large set of spectroscopic data presented should facilitate the refinement of line lists for the 12CH and 16OH radicals. For both molecules hyperfine-resolved experimental transitions have also been considered, forming SNs independent from the primary SNs. [ABSTRACT FROM AUTHOR]

The technique of Noise-Immune Cavity Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS) is employed to detect rovibrational transitions of H 2 16 O at wavelengths of 1.4 μ m. This intracavity-saturation approach narrows down the typical Doppler-broadened linewidths of about 600 MHz to the sub-MHz domain. The locking of the spectroscopy laser to a frequency-comb laser and the assessment of collisional and further line broadening effects result in transition frequencies with an absolute uncertainty below 10 kHz. The lines targeted for measurement are selected by the spectroscopic-network-assisted precision spectroscopy (SNAPS) approach. The principal aim is to derive precise and accurate relative energies from a limited set of Doppler-free transitions H 2 16 O . The 71 newly observed lines, combined with further highly accurate literature transitions, allow the determination of the relative energies for all of the 59 rovibrational states up to J = 6 within the (v 1 v 2 v 3) = (2 0 0) vibrational parent of H 2 16 O , where J is the overall rotational quantum number and v 1 , v 2 , and v 3 are quantum numbers associated with the symmetric stretch, bend, and antisymmetric stretch normal modes, respectively. An experimental curiosity of this study is that for strong transitions an apparent signal inversion in the Lamb-dip spectra is observed; a novelty reserved to the NICE-OHMS technique. [ABSTRACT FROM AUTHOR]

The linear molecular ions H2He+, HHe +2 , and He +3 are the central units (chromophores) of certain He-solvated complexes of the H2He +n , HHe +n , and He +n families, respectively. These are complexes which do exist, according to mass-spectrometry studies, up to very high n values. Apparently, for some of the H2He +n and He +n complexes, the linear symmetric tetratomic H2He +2 and the diatomic He +2 cations, respectively, may also be the central units. In this study, definitive structures, relative energies, zero-point vibrational energies, and (an)harmonic vibrational fundamentals, and, in some cases, overtones and combination bands, are established mostly for the triatomic chromophores. The study is also extended to the deuterated isotopologues D2He+, DHe +2 , and D2He +2. To facilitate and improve the electronic-structure computations performed, new atom-centered, fixed-exponent, Gaussian-type basis sets called MAX, with X = T(3), Q(4), P(5), and H(6), are designed for the H and He atoms. The focal-point-analysis (FPA) technique is employed to determine definitive relative energies with tight uncertainties for reactions involving the molecular ions. The FPA results determined include the 0 K proton and deuteron affinities of the 4He atom, 14 875(9) cm−1 [177.95(11) kJ mol−1] and 15 229(8) cm−1 [182.18(10) kJ mol−1], respectively, the dissociation energies of the He +2 → He+ + He, HHe +2 → HHe+ + He, and He +3 → He +2 + He reactions, 19 099(13) cm−1 [228.48(16) kJ mol−1], 3948(7) cm−1 [47.23(8) kJ mol−1], and 1401(12) cm−1 [16.76(14) kJ mol−1], respectively, the dissociation energy of the DHe +2 → DHe+ + He reaction, 4033(6) cm−1 [48.25(7) kJ mol−1], the isomerization energy between the two linear isomers of the [H, He, He]+ system, 3828(40) cm−1 [45.79(48) kJ mol−1], and the dissociation energies of the H2He+ → H +2 + He and the H2He +2 → H2He+ + He reactions, 1789(4) cm−1 [21.40(5) kJ mol−1] and 435(6) cm−1 [5.20(7) kJ mol−1], respectively. The FPA estimates of the first dissociation energy of D2He+ and D2He +2 are 1986(4) cm−1 [23.76(5) kJ mol−1] and 474(5) cm−1 [5.67(6) kJ mol−1], respectively. Determining the vibrational fundamentals of the triatomic chromophores with second-order vibrational perturbation theory (VPT2) and vibrational configuration interaction (VCI) techniques, both built around the Eckart–Watson Hamiltonian, proved unusually challenging. For the species studied, VPT2 has difficulties yielding dependable results, in some cases even for the fundamentals of the H-containing molecular cations, while carefully executed VCI computations yield considerably improved spectroscopic results. In a few cases unusually large anharmonic corrections to the fundamentals, on the order of 15% of the harmonic value, have been observed. [ABSTRACT FROM AUTHOR]

Motivated by recent experiments, the laser‐induced alignment‐and‐orientation (A&O) dynamics of the prolate symmetric top CH3X (X = F, Cl, Br, I) molecules is investigated, with particular emphasis on the effect of halogen substitution on the rotational constants, dipole moments, and polarizabilities of these species, as these quantities determine the A&O dynamics. Insight into possible control schemes for preferred A&O dynamics of halogenated molecules and best practices for A&O simulations are provided, as well. It is shown that for accurate A&O ‐dynamics simulations it is necessary to employ large basis sets and high levels of electron correlation when computing the rotational constants, dipole moments, and polarizabilities. The benchmark‐quality values of these molecular parameters, corresponding to the equilibrium, as well as the vibrationally averaged structures are obtained with the help of the focal‐point analysis (FPA) technique and explicit electronic‐structure computations utilizing the gold‐standard CCSD(T) approach, basis sets up to quintuple‐zeta quality, core‐correlation contributions and, in particular, relativistic effects for CH3Br and CH3I. It is shown that the different A&O behavior of the CH3X molecules in the optical regime is mostly caused by the differences in their polarizability anisotropy, in other terms, the size of the halogen atom. In contrast, the A&O dynamics of the CH3X series induced by an intense few‐cycle THz pulse is mostly governed by changes in the rotational constants, due to the similar dipole moments of the CH3X molecules. The A&O dynamics is most sensitive to the B rotational constant: even the difference between its equilibrium and vibrationally‐averaged values results in noticeably different A&O dynamics. The contribution of rotational states having different symmetry, weighted by nuclear‐spin statistics, to the A&O dynamics is also studied. [ABSTRACT FROM AUTHOR]

A large set of validated experimental transitions and empirical rovibrational energy levels are reported for the fifth most abundant carbon dioxide isotopologue, 16 O 13 C 18 O (in a shorthand notation, 638). Validation of the transitions and determination of the empirical energy levels are based on a compiled and carefully checked dataset, collected from 35 literature sources, containing 12 348/7432 measured/unique lines in the wavenumber range of 578-9318 cm -1 . The MARVEL (Measured Active Rotational-Vibrational Energy Levels) protocol, built upon the theory of spectroscopic networks, not only validates the vast majority of the measured transitions, but also yields 3975 empirical rovibrational energy levels, with uncertainty estimates compliant with the experimental uncertainties of the transitions., (© 2024 The Author(s). Journal of Computational Chemistry published by Wiley Periodicals LLC.)

Empirical rovibrational energy levels are presented for the third most abundant, asymmetric carbon dioxide isotopologue, 16 O 12 C 18 O, based on a compiled dataset of experimental rovibrational transitions collected from the literature. The 52 literature sources utilized provide 19,438 measured lines with unique assignments in the wavenumber range of 2-12,676 cm -1 . The MARVEL (Measured Active Rotational-Vibrational Energy Levels) protocol, which is built upon the theory of spectroscopic networks, validates the great majority of these transitions and outputs 8786 empirical rovibrational energy levels with an uncertainty estimation based on the experimental uncertainties of the transitions. Issues found in the literature data, such as misassignment of quantum numbers, typographical errors, and misidentifications, are fixed before including them in the final MARVEL dataset and analysis. Comparison of the empirical energy-level data of this study with those in the line lists CDSD-2019 and Ames-2021 shows good overall agreement, significantly better for CDSD-2019; some issues raised by these comparisons are discussed., (© 2024 The Author(s). Journal of Computational Chemistry published by Wiley Periodicals LLC.)

A set of empirical rovibrational energy levels, obtained through the MARVEL (measured active rotational-vibrational energy levels) procedure, is presented for the   13 C   16 O   2 isotopologue of carbon dioxide. This procedure begins with the collection and analysis of experimental rovibrational transitions from the literature, allowing for a comprehensive review of the literature on the high-resolution spectroscopy of   13 C   16 O   2 , which is also presented. A total of 60 sources out of more than 750 checked provided 14,101 uniquely measured and assigned rovibrational transitions in the wavenumber range of 579-13,735 cm   - 1 . This is followed by a weighted least-squares refinement yielding the energy levels of the states involved in the measured transitions. Altogether 6318 empirical rovibrational energies have been determined for   13 C   16 O   2 . Finally, estimates have been given for the uncertainties of the empirical energies, based on the experimental uncertainties of the transitions. The detailed analysis of the lines and the spectroscopic network built from them, as well as the uncertainty estimates, all serve to pinpoint possible errors in the experimental data, such as typos, misassignment of quantum numbers, and misidentifications. Errors found in the literature data were corrected before including them in the final MARVEL dataset and analysis., (© 2024 The Authors. Journal of Computational Chemistry published by Wiley Periodicals LLC.)

This computational study of line-broadening effects is based on an accurate, analytical representation of the intermonomer potential energy surface (PES) of the CO 2  ⋅ Ar van der Waals (vdW) complex. The PES is employed to compute collisional broadening coefficients for rovibrational lines of CO 2 perturbed by Ar. The semiclassical computations are performed using the modified Robert-Bonamy approach, including real and imaginary terms, and the exact trajectory model. The lines investigated are in the 10001←00011, 01101←00001, 00011←00001, and 00031←00001 vibrational bands and the computations are repeated at multiple temperatures. The computed results are in good agreement with the available experimental values, validating both the intermonomer PES developed and the methodology used. For lines in the 01101←00001 band of CO 2 , temperature-dependent Ar-broadening coefficients are reported for the first time. The parameters presented should prove useful, among other applications, for the accurate experimental determination of CO 2 and Ar abundances in planetary atmospheres., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Lamb dips of twenty lines in the P, Q, and R branches of the ν 1 + ν 3 + ν 4 1 vibrational band of 12 C 2 H 2 , in the spectral window of 7125-7230 cm -1 , have been measured using an upgraded comb-calibrated frequency-stabilized cavity ring-down spectrometer, designed for extensive sub-Doppler measurements. Due to the large number of carefully executed Lamb-dip experiments, and to the extrapolation of absolute frequencies to zero pressure in each case, the combined average uncertainty of the measured line-center positions is 15 kHz (5 × 10 -7 cm -1 ) with a 2-σ confidence level. Selection of the twenty lines was based on the theory of spectroscopic networks (SN), ensuring that a large number of transitions, measured previously by precision-spectroscopy investigations, could be connected to the para and ortho principal components of the SN of 12 C 2 H 2 . The assembled SN contains 331 highly precise transitions, 119 and 121 of which are in the ortho and para principal components, respectively, while the rest remain in floating components. The para - and ortho - 12 C 2 H 2 energy-level lists, determined during the present study, contain 82 and 80 entries, respectively, with an accuracy similar to that of the lines. Based on the newly assembled lists of para - and ortho - 12 C 2 H 2 empirical energy levels, a line list, called TenkHz, has been generated. The TenkHz line list contains 282 entries in the spectral range of 5898.97-7258.87 cm -1 ; thus far, only 149 of them have been measured directly via precision spectroscopy. The TenkHz line list includes 35 intense lines that are missing in the HITRAN2020 database.

Experimental and computational results about the structure, dynamics, and rovibrational spectra of protonated methane have challenged a considerable number of traditional chemical concepts. Hereby theoretical and computational results are provided about the dynamical structure of CH 5 + . It is shown that the ground vibrational state investigated thus far by computations, forbidden by nuclear-spin statistics, has a structure similar to the first allowed vibrational state and, in fact, the structures of all vibrational states significantly below 200 cm -1 are highly similar. Spatial delocalization of the nuclei, determined by nuclear densities computed from accurate variational vibrational wave functions, turns out to be limited when viewed in the body-fixed frame, confirming that the effective structure of CH 5 + is well described as a CH 3 + tripod with a H 2 unit on top of it. The interesting and unusual qualitative aspects of the sophisticated state-dependent variational results receive full explanation via simple quantum-graph models.

A non-linear spectroscopic study of the HDO molecule is performed in the wavelength range of 1.36-1.42 μ m using noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS). More than 100 rovibrational Lamb dips are recorded, with an experimental precision of 2-20 kHz, related to the first overtone of the O-H stretch fundamental of HD 16 O and HD 18 O. Significant perturbations, including distortions, shifts, and splittings, have been observed for a number of Lamb dips. These spectral perturbations are traced back to an AC-Stark effect, arising due to the strong laser field applied in all saturation-spectroscopy experiments. The AC-Stark effect mixes parity pairs, that is pairs of rovibrational states whose assignment differs solely in the K c quantum number, where K c is part of the standard J K a , K c asymmetric-top rotational label. Parity-pair mixing seems to be especially large for parity pairs with K a  ≥ 3, whereby their energy splittings become as small as a few MHz, resulting in multi-component asymmetric Lamb-dip profiles of gradually increasing complexity. These complex profiles often include crossover resonances. This effect is well known in saturation spectroscopy, but has not been reported in combination with parity-pair mixing. Parity-pair mixing is not seen in H2 16O and H2 18O, because their parity pairs correspond to ortho and para nuclear-spin isomers, whose interaction is prohibited. Despite the frequency shifts observed for HD 16 O and HD 18 O, the absolute accuracy of the detected transitions still exceeds that achievable by Doppler-limited techniques.

Detailed understanding of the energy-level structure of the quantum states as well as of the rovibronic spectra of the ethylidyne (CH) and the hydroxyl (OH) radicals is mandatory for a multitude of modelling efforts within multiple chemical, combustion, astrophysical, and atmospheric environments. Accurate empirical rovibronic energy levels, with associated uncertainties, are reported for the low-lying doublet electronic states of 12 CH and 16 OH, using the Measured Active Rotational-Vibrational Energy Levels (MARVEL) algorithm. For 12 CH, a total of 1521 empirical energy levels are determined in the primary spectroscopic network (SN) of the radical, corresponding to the following seven electronic states: X 2 Π, A 2 Δ, B 2 Σ - , C 2 Σ + , D 2 Π, E 2 Σ + , and F 2 Σ + . The energy levels are derived from 6348 experimentally measured and validated transitions, collected from 29 sources. For 16 OH, the lowest four doublet electronic states, X 2 Π, A 2 Σ + , B 2 Σ + , and C 2 Σ + , are considered, and a careful analysis and validation of 15 938 rovibronic transitions, collected from 45 sources, results in 1624 empirical rovibronic energy levels. The large set of spectroscopic data presented should facilitate the refinement of line lists for the 12 CH and 16 OH radicals. For both molecules hyperfine-resolved experimental transitions have also been considered, forming SNs independent from the primary SNs.

The linear molecular ions H 2 He + , HHe+2, and He+3 are the central units (chromophores) of certain He-solvated complexes of the H 2 He+n, HHe+n, and He+n families, respectively. These are complexes which do exist, according to mass-spectrometry studies, up to very high n values. Apparently, for some of the H 2 He+n and He+n complexes, the linear symmetric tetratomic H 2 He+2 and the diatomic He+2 cations, respectively, may also be the central units. In this study, definitive structures, relative energies, zero-point vibrational energies, and (an)harmonic vibrational fundamentals, and, in some cases, overtones and combination bands, are established mostly for the triatomic chromophores. The study is also extended to the deuterated isotopologues D 2 He + , DHe+2, and D 2 He+2. To facilitate and improve the electronic-structure computations performed, new atom-centered, fixed-exponent, Gaussian-type basis sets called MA X , with X = T(3), Q(4), P(5), and H(6), are designed for the H and He atoms. The focal-point-analysis (FPA) technique is employed to determine definitive relative energies with tight uncertainties for reactions involving the molecular ions. The FPA results determined include the 0 K proton and deuteron affinities of the 4 He atom, 14 875(9) cm -1 [177.95(11) kJ mol -1 ] and 15 229(8) cm -1 [182.18(10) kJ mol -1 ], respectively, the dissociation energies of the He+2 → He + + He, HHe+2 → HHe + + He, and He+3 → He+2 + He reactions, 19 099(13) cm -1 [228.48(16) kJ mol -1 ], 3948(7) cm -1 [47.23(8) kJ mol -1 ], and 1401(12) cm -1 [16.76(14) kJ mol -1 ], respectively, the dissociation energy of the DHe+2 → DHe + + He reaction, 4033(6) cm -1 [48.25(7) kJ mol -1 ], the isomerization energy between the two linear isomers of the [H, He, He] + system, 3828(40) cm -1 [45.79(48) kJ mol -1 ], and the dissociation energies of the H 2 He + → H+2 + He and the H 2 He+2 → H 2 He + + He reactions, 1789(4) cm -1 [21.40(5) kJ mol -1 ] and 435(6) cm -1 [5.20(7) kJ mol -1 ], respectively. The FPA estimates of the first dissociation energy of D 2 He + and D 2 He+2 are 1986(4) cm -1 [23.76(5) kJ mol -1 ] and 474(5) cm -1 [5.67(6) kJ mol -1 ], respectively. Determining the vibrational fundamentals of the triatomic chromophores with second-order vibrational perturbation theory (VPT2) and vibrational configuration interaction (VCI) techniques, both built around the Eckart-Watson Hamiltonian, proved unusually challenging. For the species studied, VPT2 has difficulties yielding dependable results, in some cases even for the fundamentals of the H-containing molecular cations, while carefully executed VCI computations yield considerably improved spectroscopic results. In a few cases unusually large anharmonic corrections to the fundamentals, on the order of 15% of the harmonic value, have been observed.