Vibration-rotation Transitions Research Articles

Anharmonic Vibrational Spectroscopy of Germanium-Containing Clusters, GexC4-x and GexSi4-x (x = 0-4), for Interstellar Detection.

An extensive, high-level theoretical study on tetra-atomic germanium carbide/silicide clusters is presented. Accurate harmonic and anharmonic vibrational frequencies and rotational constants are calculated at the CCSD(T)-F12a(b)/cc-pVT(Q)Z-F12 levels of theory. With growing capabilities to discern more of the chemical composition of the interstellar medium (ISM), an accurate database of reference material is required. The presence of carbon is ubiquitous in the ISM, and silicon is known to be present in interstellar dust grains; however, germanium-containing molecules remain elusive. To begin understanding the presence and role of germanium in the ISM, we present this study of the vibrational and rotational spectroscopic properties of various germanium-containing molecules to aid in their potential identification in the ISM with modern observational tools such as the James Webb Space Telescope. Structures studied herein include rhomboidal (r-), diamond (d-), and trapezoidal (t-) tetra-atomic molecules of the form GexC4-x and GexSi4-x, where x = 0-4. The most promising structure for detection is r-Ge2C2 via the ν4 mode with a frequency of 802.7 cm-1 (12.5 μm) and an intensity of 307.2 km mol-1. Other molecules that are potentially detectable, i.e., through vibrational modes or rotational transitions, include r-Ge3C, r-GeSi3, d-GeC3, r-GeC3, and t-Ge2C2.

Fermi Resonance and the Quantum Mechanical Basis of Global Warming

Although the scientific principles of anthropogenic climate change are well-established, existing calculations of the warming effect of carbon dioxide rely on spectral absorption databases, which obscures the physical foundations of the climate problem. Here, we show how CO2 radiative forcing can be expressed via a first-principles description of the molecule’s key vibrational-rotational transitions. Our analysis elucidates the dependence of carbon dioxide’s effectiveness as a greenhouse gas on the Fermi resonance between the symmetric stretch mode ν 1 and bending mode ν 2. It is remarkable that an apparently accidental quantum resonance in an otherwise ordinary three-atom molecule has had such a large impact on our planet’s climate over geologic time, and will also help determine its future warming due to human activity. In addition to providing a simple explanation of CO2 radiative forcing on Earth, our results may have implications for understanding radiation and climate on other planets.

Characterizing amyloid protein conformation with a multi-resonant metasurface based biosensor in the infrared window.

Misfolding of amyloid protein will cause neurodegeneration and trigger conformational disease. The lack of an effective detection approach is a brake on unveiling the mechanism of protein misfolding. We theoretically proposed a novel metasurface-based biosensor for characterizing the protein's conformation. The coupling complementary split ring resonator (cSRR) was engineered to manipulate incident waves in the near-infrared (NIR) and mid-infrared (MIR) windows at the same sensing surface. The cSRRs had the advantages of intensifying the electric field and sharpening the resonance profile, resulting in a highly qualified biosensing performance. In the NIR window, the biolayer's refractive index and thickness change were detected by the dual-wavelength, which resolved into an optogeometrical parameter of the amyloid biolayer. In the MIR window, the resonant wave specifically triggered the rotation-vibration transition of amyloid protein molecules with different conformations, which was shown as the unique Amide I and II bands in the fingerprint spectrum. Thus, our proposed biosensor presented sensitive detection of biolayer and specific identification of constituent molecules. It is helpful to interpret the protein's misfolding behavior on the molecular level by associating the biolayer's structure and the constituent molecule's conformational change.

Analysis of the calculated and observed X-X ro-vibrational transition intensities in molecular hydrogen

The potential-energy and quadrupole-moment functions of the H2 ground electronic state are well known in literature (Komasa et al., 2019; Wolniewicz et al., 1998), and the line list of the vibrational–rotational transitions was calculated (Roueff et al., 2019). In this paper, we analyze the calculated intensities in order to learn how the intensities will change when analytic quadrupole-moment functions fitted to the ab initio and experimental data are used instead of spline-interpolated functions. We found that the use of splines does not deteriorate the intensities and does not lead to nonphysical saturation, as in heavier molecules, owing to the high precision of the ab initio data and the high density of the grid. The accuracy of the calculated intensities is estimated up to high overtones. Extraction of new spectroscopic information from the observational data that supplements the laboratory measurements is performed. The laboratory and observational data do not help increase the quality of the analytic functions. Numerous anomalies resulting from the destructive interference are identified in the calculated line lists, some of them being situated within the recently observed spectral regions, 1.5–2.5μm. The intensities of these anomalies can be sensitive to the form of the molecular functions as well as to the proton-to-electron mass ratio. In this connection, the similar Le Roy anomalies (Brown and LeRoy, 1973; Le Roy and Vrscay, 1975) also arising due to the destructive interference in the Lyman and Werner systems are discussed.

Radiative forcing due to carbon dioxide decomposed into its component vibrational bands†

AbstractThe radiative forcing (RF) of climate change due to increases in carbon dioxide (CO2) concentration is primarily in the wavenumber region 500–850 cm−1 (wavelengths of approximately 12 to 20 μm). It originates from absorption and emission of infrared radiation due to vibrational–rotational transitions of the CO2 molecule. While this RF has been the subject of intense and detailed study, to date, the contribution of different vibrational transitions to this forcing has not been explored. This article presents an analysis of radiative transfer calculations that quantify the role of different vibrational transitions and illustrates that while the fundamental bending mode contributes nearly 90% of the total infrared intensity, it contributes less than half of the RF at present‐day CO2 concentrations; this is because the absorption at the centre of this fundamental band is so intense that the effect of additional CO2 is strongly muted. By successively adding in additional CO2 bands to the calculations, it is demonstrated that a key spectroscopic phenomenon, known as Fermi Resonance (an interaction between excited states of the bending and the symmetric stretching modes of CO2) leads to a significant spreading of the infrared intensity to both higher and lower wavenumbers, where the fundamental bending mode is less important. The Fermi Resonance transitions contribute only about 4% of the total infrared intensity in this spectral region but cause more than half of the present‐day RF. The less‐abundant isotopologues of CO2 have little impact on the spectrally integrated RF, but this small contribution results from a compensation between more significant positive and negative contributions to the spectral RF. This work does not alter the results of detailed RF calculations available in the literature; rather, it helps explain the physical basis of that forcing.

King-Plot Analysis of Isotope Shifts in Simple Diatomic Molecules

We demonstrate that the isotope shift in isotopomers of diatomic molecules, where the nucleus of one of its constituent atoms is replaced by another isotope, can be expressed as the sum of a field shift and a mass shift, similar to the atomic case. We show that a linear relation holds between atomic and molecular isotopes shifts, thus extending the King-plot analysis to molecular isotope shifts. Optical isotope shifts in YbF and ZrO and infrared isotope shifts in SnH are analyzed with a molecular King-plot approach, utilizing Yb$^{+}$ and Zr$^{+}$ ionic isotope shifts and charge radii of Sn obtained with non-optical methods. The changes in the mean-squared nuclear charge radii $\delta \langle r^2 \rangle$ of $^{170-174,176}$Yb and $^{90-92,94,96}$Zr extracted from the molecular transitions are found to be in excellent agreement with the values from the spectroscopy of Yb$^{+}$ and Zr$^{+}$, respectively. On the contrary, in the case of the vibrational-rotational transition in SnH, no sensitivity to the nuclear volume could be deduced within the experimental resolution, which makes it unsuitable for the extraction of nuclear charge radii but provides insights into the molecular electronic wave function not accessible via other methods. The new opportunities offered by the molecular King-plot analysis for research in nuclear structure and molecular physics are discussed.

Multiple gas phases in supernova remnant IC 443: mapping shocked H2 with VLT/KMOS

ABSTRACT Supernovae and their remnants provide energetic feedback to the ambient interstellar medium (ISM), which is often distributed in multiple gas phases. Among them, warm molecular hydrogen (H2) often dominates the cooling of the shocked molecular ISM, which has been observed with the H2 emission lines at near-infrared wavelengths. Such studies, however, were either limited in narrow filter imaging or sparsely sampled mid-infrared spectroscopic observations with relatively poor angular resolutions. Here we present near-infrared (H and K bands) spectroscopic mosaic observations towards the A, B, C, and G regions of the supernova remnant (SNR) IC 443, with the K-band Multi-Object Spectrograph (KMOS) onboard the Very Large Telescope (VLT). We detected 20 rotational–vibrational transitions of H2, one H line (Brγ), and two [Fe ii] lines, which dominate broad-band images at both H and K bands. The spatial distribution of H2 lines at all regions is clumpy on scales from ∼0.1 down to ∼0.008 pc. The fitted excitation temperature of H2 is between 1500 and 2500 K, indicating warm shocked gas in these regions. The multigas phase comparison shows stratified shock structures in all regions, which explains the coexistence of multiple types of shocks in the same regions. Lastly, we verify the candidates of young stellar objects previously identified in these regions with our spectroscopic data, and find none of them are associated with young stars. This sets challenges to the previously proposed scenario of triggered star formation by SNR shocks in IC 443.

Fano-like Resonance due to Interference with Distant Transitions.

Narrow optical resonances of atoms or molecules have immense significance in various precision measurements, such as testing fundamental physics and the generation of primary frequency standards. In these studies, accurate transition centers derived from fitting the measured spectra are demanded, which critically rely on the knowledge of spectral line profiles. Here, we propose a new mechanism of Fano-like resonance induced by distant discrete levels and experimentally verify it with Doppler-free spectroscopy of vibration-rotational transitions of CO_{2}. The observed spectrum has an asymmetric profile and its amplitude increases quadratically with the probe laser power. Our results facilitate a broad range of topics based on narrow transitions.

CO2 Gas Temperature Sensing near Room Temperature by a Quantum Cascade Laser in Inter Pulse Mode

A non-invasive CO2 gas temperature sensing technique at or close to the room temperature range based on quantum cascade laser absorption spectroscopy is presented. The method probes thermally populated ground state and hot-band rotational-vibrational transitions of CO2 in the frequency range from 2349 to 2351 cm−1 from which the gas temperature is obtained from Boltzmann statistics. Transmission spectra are recorded by injection-current driven frequency-scans, the so-called inter pulse mode, of a pulsed distributed feedback quantum cascade laser. The statistical uncertainty (1σ) in temperature for single frequency scans with time resolution of 10 ms is 4 K and can be further reduced down to ∼50 mK by long-time averaging of about 1 min. The technique is evaluated with particular emphasis on implementation, data acquisition, data analysis and potential improvements.

Экспериментальные интенсивности линий колебательно-вращательных переходов в полосах ν1+ ν2 и ν2+ ν3 молекулы D234S

The study of the absolute line intensities in the high-resolution spectrum of the D234S molecule in the range 2300-2900 cm-1 has been carried out for the first time. As a result of the analysis, about 800 experimental intensities of vibrational-rotational transitions were obtained for the v 1 + v 2 and v 2 + v 3 bands, and a set of 6 parameters of the effective dipole moment was calculated, which reproduces the initial experimental line intensities with drms = 9.7%. A list of transitions with frequencies and line intensities in the range under study has been compiled.

Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm

Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C2H2 between 7167 and 7217 cm−1, using a frequency-comb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers. We measured the absolute center frequency of sixteen lines belonging to the 2 band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a ‘V’-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 3 and 13 kHz. This is over three orders of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene.

Re-investigation of the infrared spectrum of the NCN radical by laser magnetic resonance spectroscopy

The laser magnetic resonance (LMR) spectroscopic technique has been used to reinvestigate the mid-infrared spectrum of the NCN free radical in its Σg-3 ground electronic state. A liquid nitrogen-cooled carbon monoxide (CO) laser was used as a source of strong coherent radiation in the 1442–1484 cm−1 region of the infrared. Vibration-rotation transitions were brought into resonance with the laser frequency using magnetic flux densities up to 1.4 T. Spectra were recorded in both parallel (ΔMJ = 0) and perpendicular (ΔMJ = ±1) polarizations with ten CO laser lines. Over one hundred new absorption lines were observed in the LMR spectra and have been subsequently assigned to transitions in either the 301 fundamental band (near 1466.5 cm−1) or the 211301 hot band (near 1455.6 cm−1) of NCN in the Σg-3 ground state. An improved set of molecular parameters for NCN has been determined from a least-squares fit of all the available data on the infrared spectrum, provided by Fourier transform and LMR spectra. In the wake of an exhaustive analysis of the LMR spectra, several additional lines remain. Although chemical tests indicate these lines do not belong to NCN, it has not proved possible to identify their carrier(s).

Modelling of the 2ν1-ν1 and ν1 band transitions of 13CH4 using high resolution Raman spectroscopy measurements

The pump-probe technique for investigating vibrationally excited states via high resolution Raman spectroscopy was applied to 13CH4 methane isotopologue. The dipole transitions between A1 totally symmetric vibrational states are not active in IR spectra but these states can be efficiently studied using selective high resolution Raman spectroscopy. 80 vibration-rotation transitions, most of which belong to the 2ν1– ν1 band have been assigned in the observed Raman spectra reported in this work. Including the Raman transitions in the simultaneous data fit improves the accuracy of the effective Hamiltonian and also rovibrational upper state levels of the ν1, 2ν1 and 2ν3 (A1) bands. A more accurate model of the ν1 vibration-rotation transitions improves the interpretation of the temperature dependence of Raman spectra involving the Pentad and Tetradecad polyads.

Doppler-limited precision spectroscopy of HD at 1.4 μm : An improved determination of the R (1) center frequency

We report on the improved determination of the center frequency of a hydrogen deuteride vibration-rotation transition. As a result of a refined analysis of cavity ring-down absorption spectra, it was possible to quantify the influence of the hyperfine structure on the line center frequency of the weak 2-0 $R(1)$ line, as retrieved in the Doppler-limited regime. It turns out that ignoring the hyperfine structure leads to an underestimation of the center frequency of about 350 kHz. The updated determination gives an absolute frequency of the $R(1)$ centroid of 217 105 181.936 MHz with a global uncertainty of 76 kHz.

An improved rovibrational linelist of formaldehyde, H[formula omitted]C[formula omitted

Published high-resolution rotation-vibration transitions of H212C16O, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, ν3,ν4, and ν6 vibrational states. Of the 16 596 non-redundant transitions processed, which come from 43 sources including the present work, 16 403 could be validated, providing 5029 empirical energy levels of H212C16O with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol’s AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material.

Природа тонкой структуры вращательных уровней основного X-=SUP=-2-=/SUP=-Sigma-=SUP=-+-=/SUP=--состояния радикала CN

By means of ab initio high-level quantum-chemical calculations of non-diagonal matrix elements of spin-orbital and electron-rotational coupling between the ground X2Σ+ and excited (1--4)2Π states the observed regular effect of γ-doubling of the rotational levels of the X2Σ+ state was shown to be mainly determined by intramolecular interactions of the mentioned state with remote states (2--4)2Π. In terms of the nonadiabatic model of the effective radial Hamiltonian of the isolated electronic state, it was possible to create the analytical potential of the X2Σ+ state and the corresponding function γ (R) reproducing the frequencies of rotational and vibrational-rotational transitions (for the lowest vibrational levels ν≤3) of the CN molecule at the experimental (spectroscopic) level of accuracy.

The new nitrogen dioxide (NO2) linelist in the GEISA database and first identification of the ν1+2ν3-ν3 band of 14N16O2

We have generated new lists of line position, line intensity and line shape parameters of nitrogen dioxide (14N16O2 and 15N16O2), here labeled as “GEISA-19”, which have been included in the (Gestion et Etude des Informations Spectroscopiques Atmosphériques) GEISA database (https://geisa.aeris-data.fr/). Except for the far infrared and the 13.3 µm regions, all spectral regions of the 1153–4775 cm−1 spectral domain are significantly modified by this major update of the GEISA linelist. For the 6.2 µm and 3.4 µm spectral regions, which correspond to the strongest absorption of NO2, we proceed to a complete replacement of the lists for the first hot bands, ν2 + ν3-ν2 and ν1 +ν2 + ν3-ν2, respectively, and to the inclusion, whenever possible, of higher order hot bands involving the (1,0,0), (0,2,0) and (0,0,1), (1,1,0), (2,0,0) or (0,0,2) states as lower states. Also, the ν1 + ν3 linelist was improved for high rotational quantum numbers and the ν3 and ν1+ν3 bands for 15N16O2, which is the second most abundant isotopologue of NO2, are now included in the database. Finally several weak cold bands in the 2.2–4.9 µm region were added for the first time to the GEISA linelist. These new vibration rotation transitions were generated using existing literature data or making use of experimental data extracted from high resolution Fourier transform spectra recorded at SOLEIL for the purpose of this study. One outcome of this study was the first identification of the ν1+2ν3-ν3 hot band, leading to the first determination of the (1,0,2) energy level parameters. Also, an improved set of parameters was derived for the (0,1,1) state. The validation of the GEISA-19 linelist was performed through a detailed comparison at 296 K between computed and observed Fourier transform laboratory spectra. Also, the consistency, from one band to another, of the energy levels values was carefully checked. Finally inter-comparisons and verifications were performed using the recent versions of the HITRAN (https://hitran.org/) and HITEMP databases [R.J. Hargreaves, I. E. Gordon, L. S. Rothman, S. A. Tashkun, V. I. Perevalov, A. A. Lukashevskaya, S. N. Yurchenko, J. Tennyson, and H. S.P. Müller. J. Quant. Spectrosc. Radiat. Transf. 232 35 (2019)]. Our conclusions are that, at 296 K, GEISA-19 is of better quality than HITRAN2016-updated or HITEMP in the overall 1153–4775 cm−1 spectral region. As compared to its previous version, this new linelist will lead to an improved quality of the NO2 retrievals that will be performed for the future IASI-NG (Infrared Atmospheric Sounding Interferometer New Generation) satellite instrument (https://iasi-ng.cnes.fr/fr). However, contrary to HITEMP, GEISA-19 which does not include transitions involving high rotational quantum numbers or belonging to very high order hot bands cannot be used for hot temperature conditions.

Polarization hole burning and self-rotation of the polarization ellipse in an acetylene-filled hollow-core photonic crystal fiber

We report on the first experimental observation of the polarization ellipse self-rotation (PSR) and the polarization hole burning (PHB) nonlinear optical effects for the acetylene ( C 2 H 2 ) vibrational–rotational transitions in the 1520–1530 nm spectral range. The experiments were performed using a 1-m-long acetylene-filled hollow-core photonic crystal fiber cell at room temperature and gas pressure of 0.4–4 Torr. The PHB effect was experimentally observed as a photo-induced input polarization ellipticity change in the output light. Among all the investigated acetylene transitions P9, P7, P5, and P3, the maximum ellipticity change of ∼ 35 % was observed at zero detuning from the center of the P5 absorption line with the initial optical absorbance about 6. The obtained results are in good agreement with the theoretical predictions of a classical analysis based on the model of the acetylene molecules as gyrators (circular oscillators) with random orientations. For the inhomogeneously broadened acetylene absorption P5 line ( ∼ 500 M H z ), the PSR effect observed for tuning at the sides of the P5 line, as expected, proved to be by factor Δ ω i h / Δ ω h (inhomogeneous-to-homogeneous broadening ratio) lower than the maximum PHB. The PSR constant for these conditions proved to be about 0.1 m − 1 , which is about 2 orders of magnitude lower than that reported earlier for the alkali metal (K, Rb) vapors.

High-resolution infrared action spectroscopy of the fundamental vibrational band of CN+

Rotational-vibrational transitions of the fundamental vibrational modes of the 12C14N+ and 12C15N+ cations have been observed for the first time using a cryogenic ion trap apparatus with an action spectroscopy scheme. The lines P(3) to R(3) of 12C14N+ and R(1) to R(3) of 12C15N+ have been measured, limited by the trap temperature of approximately 4 K and the restricted tuning range of the infrared laser. Spectroscopic parameters are presented for both isotopologues, with band origins at 2000.7587(1) and 1970.321(1) cm−1, respectively, as well as an isotope independent fit combining the new and the literature data.

Constraining nucleosynthesis in two CEMP progenitors using fluorine

ABSTRACT We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429−0551 and HE 1305+0007. HE 1429−0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration–rotation transition of the HF molecule at 23358.6 Å using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429−0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = −2.53, and an F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = −2.28. Our new derived F abundance in HE 1429−0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429−0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429−0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.