Vibration-rotation Energy Levels Research Articles

Ab initio the thermodynamic properties and UV spectrum of AlCl+

AlCl+ as a potential interstellar molecule has attracted significant attention, but gaps remain in our understanding of its thermodynamic properties and spectral line intensities. This study employed the icMRCI+Q method to compute potential energy curves for the 13 Λ-S states of AlCl+. Based on these curves, spectroscopic parameters and vibrational–rotational energy levels were determined. Subsequently, partition functions were calculated over a temperature range from 50 K to 10000 K, and the thermodynamic properties were derived. Using transition dipole moments, the UV spectra for transitions from the ground state (X2Σ+) to the third excited state (22Π) were computed at 298.15 K.

Potential energy curves for F2, Cl2, and Br2 with the i-DMFT method.

The potential energy curves for dihalogens (F2, Cl2, and Br2) are calculated with the i-DMFT method proposed recently [Wang and Baerends, Phys. Rev. Lett. 128, 013001]. All electrons are correlated in a set of self-consistent-field eigenvalue equations, with the orbital occupation numbers obeying the Fermi-Dirac distribution. The only input is the dissociation energies of the molecules, which are usually available from an experimental database. The quality of the computed potential energy curve is examined by extracting spectroscopic parameters and rotation-vibration energy levels, which are compared with experiment data and other theoretical calculations.

MARVEL analysis of high-resolution rovibrational spectra of 16O12C18O.

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.

Ab Initio Ground-State Potential Energy Function and Vibration-Rotation Energy Levels of Magnesium Monohydride.

The accurate potential energy function of magnesium monohydride in its X2Σ+ state has been determined from ab initio calculations. The vibration-rotation energy levels of the main isotopologue 24MgH were predicted to near the "spectroscopic" accuracy. The scalar relativistic, adiabatic, and nonadiabatic effects were discussed.

ExoMol line lists – LVIII. High-temperature molecular line list of carbonyl sulphide (OCS)

ABSTRACT A new molecular line list covering wavelengths λ > 1 μm (the 0–10 000 cm−1 range) for the main isotopologue of carbonyl sulphide 16O12C32S is presented. The OCS line list, named OYT8, contains almost 2.5 billion transitions between 2.4 million rotation-vibration energy levels with the total angular momentum up to J = 223. It is suitable for high-temperature environments up to T = 2000 K. Line list calculations were performed with the variational nuclear motion code trove in conjunction with a highly accurate, empirically refined potential energy surface and a newly computed ab initio dipole moment surface of OCS. The OYT8 line list is adapted for high-resolution applications by replacing computed energy levels with empirically derived values of OCS where available. Comparisons of the OYT8 line list with other OCS line lists and spectra yields excellent agreement for both strong and weak spectroscopic bands. The increased coverage of the OYT8 line list and the many new spectral features that are available will greatly facilitate the future observation of OCS on exoplanets. Carbonyl sulphide joins a growing number of sulphur-bearing molecules available from the ExoMol database. The OYT8 line list along with the associated temperature- and pressure-dependent molecular opacities can be downloaded from www.exomol.com and the CDS astronomical database.

Cationized orthogonal triad as a photosensitizer with enhanced synergistic antimicrobial activity

Single-molecule-based synergistic phototherapy holds great potential for antimicrobial treatment. Herein, we report an orthogonal molecular cationization strategy to improve the reactive oxygen species (ROS) and hyperthermia generation of heptamethine cyanine (Cy7) for photodynamic and photothermal treatments of bacterial infections. Cationic pyridine (Py) is introduced at the meso‑position of the asymmetric Cy7 with intramolecular charge transfer (ICT) to construct an atypical electron-transfer triad, which reduces ΔES1-S0, circumvents rapid charge recombination, and simultaneously enhances intersystem crossing (ISC) based on spin-orbit charge-transfer ISC (SOCT-ISC) mechanism. This unique molecular construction produces anti-Stokes luminescence (ASL) because the rotatable CN bond enriched in high vibrational-rotational energy levels improves hot-band absorption (HBA) efficiency. The obtained triad exhibits higher singlet oxygen quantum yield and photothermal conversion efficiency compared to indocyanine green (ICG) under irradiation above 800 nm. Cationization with Py enables the triad to target bacteria via intense electrostatic attractions, as well as biocidal property against a broad spectrum of bacteria in the dark. Moreover, the triad under irradiation can enhance biofilm eradication performance in vitro and statistically improve healing efficacy of MRSA-infected wound in mice. Thus, this work provides a simple but effective strategy to design small-molecule photosensitizers for synergistic phototherapy of bacterial infections. Statement of SignificanceWe developed an orthogonal molecular cationization strategy to enhance the reactive oxygen species and thermal effects of heptamethine cyanine (Cy7) for photodynamic and photothermal treatments of bacterial infections. Specifically, cationic pyridine (Py) was introduced at the meso‑position of the asymmetric Cy7 to construct an atypical electron-transfer triad, which reduced ΔES1-S0, circumvented rapid charge recombination, and simultaneously enhanced intersystem crossing (ISC). This triad, with a rotatable CN bond, produced anti-Stokes luminescence due to hot-band absorption. The triad enhanced antimicrobial performance and statistically improved the healing efficacy of MRSA-infected wounds in mice. This site-specific cationization strategy may provide insights into the design of small molecule-based photosensitizers for synergistic phototherapy of bacterial infections.

Empirical rovibrational energy levels for nitrous oxide

A survey of the huge number of measured rovibrational transitions of the 14N216O isotopologue of nitrous oxide is performed which either confirms the positions, the assignments, and the uncertainties of the measurements or refutes at least one of them. Data from 95 literature sources are analyzed and their assignments adjusted to a uniform set of polyads and associated counting numbers. This is an important result of the present study and this canonical set of vibrational state assignments is recommended for future studies. The adjusted list of 67930 transitions (43246 unique ones) then underwent a thorough Marvel (Measured Active Rotational–Vibrational Energy Levels) analysis, yielding 17561 empirical rovibrational energy levels. Uncertainties for these levels are determined using a newly implemented bootstrap approach. The bootstrap uncertainties indicate that the uncertainties for about 1.5% of the energy levels had to be increased significantly, often by more than 10 times compared to previous level uncertainty estimates. This study yields empirical values for 78 band origins of 14N216O for states with ℓ=0, where ℓ is the vibrational angular momentum quantum number. The measured transitions and the empirical energy levels are compared to the SISAM and the recent NOSL-296 line lists with the result that while the overall agreement is good, there are still a number of issues requiring further careful experimental and modeling studies.

Empirical rovibrational energy levels for methane

A Marvel (Measured Active Rotational Vibrational Energy Levels) analysis of the available spectroscopic data on methane (12C1H4) is performed. A total of 82173 measured rovibrational transitions were gathered from 96 literature sources and put through the Marvel procedure which led to the determination of 23292 empirical energy levels with uncertainties, up to 9900 cm−1 covering the lowest eight polyads. A comparison with Effective Hamiltonian evaluated levels, variational calculations by the TheoReTS project, and the MeCaSDa database is performed. The new levels generated will be used to improve the upcoming ExoMol MM line list.

MARVEL analysis of high-resolution rovibrational spectra of C O .

A set of empirical rovibrational energy levels, obtained through the MARVEL (measured active rotational-vibrational energy levels) procedure, is presented for the C O 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 C O , which is also presented. A total of 60sources out of more than 750 checked provided 14,101uniquely measured and assigned rovibrational transitions in the wavenumber range of 579-13,735 cm . This is followed by a weighted least-squares refinement yielding the energy levels of the states involved in the measured transitions. Altogether 6318empirical rovibrational energies have been determined for C O . 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.

A highly accurate potential energy surface for carbonyl sulphide (OCS): how important are the ab initio calculations?

Ab initio quantum chemical methods can produce accurate molecular potential energy surfaces (PESs) capable of predicting the fundamental vibrational wavenumbers to within 1 cm-1. However, for high-resolution applications this is simply not good enough and empirical refinement is necessary, i.e. adjusting the PES to better match laboratory spectroscopic data. Here, the impact of the underlying ab initio calculations is rigorously investigated within the context of empirical refinement. For carbonyl sulphide (OCS), state-of-the-art electronic structure calculations are employed to construct higher- and lower-level ab initio PESs, which are then empirically refined in near-identical procedures. The initial ab initio calculations are shown to considerably affect the accuracy of the final refined PES, with an order-of-magnitude improvement in computed rotation-vibration energy levels achieved for OCS. In demonstrating this, the most accurate PES of the electronic ground state of OCS is produced, reproducing the fundamentals with a root-mean-square error (RMSE) of 0.004 cm-1, and 884 rovibrational energy levels below 14 000 cm-1 with an RMSE of 0.060 cm-1.

ExoMol line lists – LII. Line lists for the methylidyne cation (CH+)

ABSTRACT Comprehensive and accurate rovibronic line lists for the X 1Σ+ and A 1Π states of 12C1H+ and 13C1H+ which should be applicable up to temperatures of 5000 K are presented. Available empirical potential energy curves and high-level ab initio dipole and transition dipole moment curves are used with the program level to compute rovibronic energy levels and Einstein A coefficients. Λ-doubling is incorporated into the energy levels and A-coefficients involving the A 1Π state using an empirical method. For 12C1H+, line positions are improved by using both laboratory and astronomical observational spectra as input to the MARVEL (Measured Active Rotational-Vibrational Energy Levels) procedure. The 12C1H+ line list contains 1505 states and 34 194 transitions over the frequency range of 0–33 010 cm−1 (λ > 300 nm). Comparisons with observed astronomical and laboratory spectra give very good agreement. The PYT CH+ line lists and partition functions are available from the ExoMol database at www.exomol.com.

Empirical rovibrational energy levels for carbonyl sulphide

ABSTRACT An exhaustive review of the measured rovibrational transitions of the 16 O 12 C 32 S isotopologue of carbonyl sulphide is undertaken. A comprehensive analysis of data from 100 papers is carried out using a consistent set of harmonic oscillator quantum numbers which are recommended for future studies. A corrected compilation of 14,071 OCS transitions is then subjected to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) analysis, resulting in 5729 empirical energy levels. The uncertainties corresponding to these levels are analysed using different procedures; the newly implemented bootstrap method is used to provide final uncertainties.

Empirical rovibronic energy levels of C3

ABSTRACT The carbon trimer, C 3 also known as propadienediylidene, is a quasi-linear molecule with an unusual electronic structure and a very flat bending potential in its ground electronic state. C 3 is an important species in astrophysics and carbon plasmas. Observed transition wavenumbers within and between the X ~ 1 Σ g + and A ~ 1 Π u states of C 3 are extracted from 21 papers and then subjected to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) analysis: a corrected list of 4940 transitions are inverted to yield 1887 empirical energy levels. Uncertainties for these levels are determined using a newly implemented bootstrap method. These levels will provide input for developing a full spectroscopic model for C 3 which can used to generate a line list for the X ~ 1 Σ g + and A ~ 1 Π u states.

ExoMol line lists – LI. Molecular line lists for lithium hydroxide (LiOH)

ABSTRACT New molecular line lists for lithium hydroxide (6Li16O1H and 7Li16O1H isotopologues) covering wavelengths λ > 1 $\mu$m (0–10 000 cm−1 range) are presented. Each line list contains around 300 million transitions between rotation–vibration energy levels with total angular momentum up to J = 95, applicable for temperatures up to T ≈ 3500 K. Line list calculations were based on a previously published, high-level ab initio potential energy surface and a newly computed dipole moment surface of the ground $\tilde{X}\, ^1\Sigma ^+$ electronic state. Lithium-containing molecules are important in a variety of stellar objects and there is potential for LiOH to be observed in the atmospheres of exoplanets. Transit spectra are simulated using the rocky super-Earth 55 Cancri e as an example with two different atmospheric scenarios including LiOH. This work provides the first, comprehensive line lists of LiOH to facilitate its future molecular detection. The OYT7 line lists along with the associated temperature- and pressure-dependent molecular opacities can be downloaded from the ExoMol database at www.exomol.com and the CDS astronomical database.

Ab Initio Potential Energy Surface and Vibration-Rotation Energy Levels of Aluminum Monohydroxide.

The potential energy surface and vibration-rotation energy levels of aluminum monohydroxide in the X̃ 1A' electronic state have been determined from ab initio calculations. The equilibrium configuration of the AlOH molecule was found to be bent, although with a wide AlOH angle of 163° and a small barrier to linearity of just 4 cm-1. The AlOH molecule was definitely confirmed to be quasilinear. The predicted spectroscopic constants of the AlOH, AlOD, 26AlOH, and Al18OH isotopologues can be useful in a future analysis of high-resolution vibration-rotation spectra of these species.

Optical frequency comb Fourier transform spectroscopy of formaldehyde in the 1250 to 1390 cm−1 range: Experimental line list and improved MARVEL analysis

We use optical frequency comb Fourier transform spectroscopy to record high-resolution, low-pressure, room-temperature spectra of formaldehyde (H212C16O) in the range of 1250 to 1390 cm−1. Through line-by-line fitting, we retrieve line positions and intensities of 747 rovibrational transitions: 558 from the ν6 band, 129 from the ν4 band, and 14 from the ν3 band, as well as 46 from four different hot bands. We incorporate the accurate and precise line positions (0.4 MHz median uncertainty) into the MARVEL (measured active vibration-rotation energy levels) analysis of the H2CO spectrum. This increases the number of MARVEL-predicted energy levels by 82 and of rovibrational transitions by 5382, and substantially reduces uncertainties of MARVEL-derived H2CO energy levels over a large range: from pure rotational levels below 200 cm−1 up to multiply excited vibrational levels at 6000 cm−1. This work is an important step toward filling the gaps in formaldehyde data in the HITRAN database.

Joint survey of the experimental high-resolution spectra of H16O37Cl and H16O35Cl with a reanalysis of the [formula omitted] band

The study starts with a detailed analysis of all the high-resolution rovibrational transitions measured for the minor hypochlorous acid isotopologue H16O37Cl, employing the Marvel (Measured Active Rotational-Vibrational Energy Levels) procedure. The survey considers 16 sources, the wavenumber coverage of the transitions extends from the microwave to the visible region, corresponding to 13 vibrational parent states. Experimental transitions data from older (1994, 1996, and 2000) sources, not published explicitly in the original papers, are presented in here for the first time; the newly reported transitions represent about one third of all the transitions assigned for H16O37Cl. Then a minor update to the transitions and levels of H16O35Cl published in J. Mol. Spectrosc. 384 (2022) 111561 is provided. Proper labelling and internal consistency of the transitions and the empirical rovibrational energies of H16O35Cl and H16O37Cl is enforced utilizing effective Hamiltonian (EH) and first-principles variational nuclear-motion computation results. An iteratively updated line list, based on empirical and EH rovibrational energy levels and first-principles intensities, is used to assign a significant number of new transitions in the 2ν2 band (2300–2800 cm−1) for both isotopologues. At the end, for H16O35Cl/H16O37Cl, from the total of 20349/10266 experimentally measured transitions considered, 20119/10124 could be validated, allowing the derivation of 5760/3933 empirical rovibrational energy levels with well-defined uncertainties. Improved parameters for an effective Hamiltonian corresponding to the 2ν2 state are given. A comparison with data in the canonical spectroscopic line-by-line database HITRAN is also provided.

LED-based Fourier spectroscopy of HD17O in the range of 10000-11300 cm−1. Energy structure of (022), (102), (080), (400), (003), (211), (051), (131), (320), (032), (112) resonating states

We report our investigation of the HD17О absorption spectrum in the range of 10,000–11,300 cm−1. The measurements were performed using an IFS-125 M Fourier spectrometer with a resolution of 0.02 cm−1 at a pressure of 29 mbar and an optical path length of 2400 cm. An EDEN-1L53 LED was used as a light source giving a maximum radiation intensity in the region of 0.95 µm. The absorption spectrum was analyzed using a set of software programs capable of searching for spectral lines, fitting line parameters, and making line assignments. As a result of the analysis, experimental information was obtained for the first time on the parameters of 1137 spectral lines assigned to 12 vibrational bands of HD17О, and 364 vibrational-rotational energy levels of the (022), (102), (080), (400), (003), (211), (051), (131), (320), (032), and (112) vibrational states were determined. The obtained experimental results are compared with calculated data.

Ab initio potential energy surface and vibration-rotation energy levels of magnesium monohydroxide revisited

The accurate potential energy surface of magnesium monohydroxide, MgOH, in its ground electronic state X˜2Σ+ has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. The core-electron correlation, higher-order electron correlation, scalar relativistic, and adiabatic effects were taken into account. The equilibrium configuration of the MgOH molecule was confirmed to be linear, although with the bending potential energy function being very flat near the minimum. The vibration–rotation-spin energy levels of the MgOH, MgOD, 25MgOH, and 26MgOH isotopologues were predicted using a variational approach. The spectroscopic constants of these isotopologues were determined to high accuracy.

NASA Polynomial representation of molecular specific heats

So called NASA polynomials are widely used in plasma and combustion models to represent the specific heat of molecules as a function of temperature. In this work, we compute seven-term NASA polynomials for 464 molecules of which 44 are cations and 9 are anions; polynomials are not currently available for almost 200 of these species. Calculation of the NASA polynomials utilises data provided by the ExoMol database, the HITRAN database, the diatomic partition functions computed by Barklem and Collet, and the JANAF thermodynamic tables. Our results are compared against existing polynomial compilations where available, and for cases where there are multiple datasets the recommended polynomials are identified. As proposed in the original compilation, the seven-term polynomials are fitted separately for the temperature ranges 200 – 1000 K and 1000 – 6000 K. In general, different data sources give good agreement in the lower temperature range but there are significant discrepancies at higher temperatures, which can be attributed to the underlying assumptions made about highly excited rotation-vibration energy levels.