Compact Spatial Heterodyne Spectrographs for Future Space-Based Observations: Instrument Modeling and Applications.

High-resolution spectroscopy employing spatial heterodyne spectrographs (SHS) holds significant promise for forthcoming space missions, building upon its established track record in science applications. Notably, it offers exceptional performance and cost- effectiveness in the ultraviolet-visual (UV-Vis) region compared to contemporary instruments. SHS instruments provide high-resolution capabilities and substantially larger etendues than similar resolving power instruments. This study introduces a comprehensive Python-based SHS model integrated with a user-friendly web scraping interface for target star selection, parameter generation, and 2D interferogram creation. Our SHS model demonstrates double the resolving power of a grating spectrometer and a throughput comparable to a Fourier transform spectrometer (FTS) but without moving parts, enhancing robustness for deployment in space. The interferogram processing algorithm includes flat-fielding, bias removal, apodization, and an inverse Fourier transform (IFT) for accurate spectrum retrieval. Despite bandwidth limitations due to resolving power constraints, SHS models excel in applications requiring high spectral resolution over narrow wavelength ranges, such as studying isotopic emission lines. The model provides optimization results and trade-offs for system parameters, ensuring precise spectral recovery with realistic signal-to-noise ratio (SNR) values. SHS is versatile and effective for various scientific applications, including investigating atomic and molecular emissions from comets, planetary atmospheres, the Earth's atmosphere, the Sun, and the interstellar medium (ISM). This research significantly contributes to expediting the development and deployment of SHS instruments, demonstrating their potential across numerous scientific domains.

High Resolution Infrared Spectroscopy in Support of Ozone Atmospheric Monitoring and Validation of the Potential Energy Function.

The first part of this review is a brief reminder of general information concerning atmospheric ozone, particularly related to its formation, destruction, observations of its decrease in the stratosphere, and its increase in the troposphere as a result of anthropogenic actions and solutions. A few words are said about the abandonment of the Airbus project Alliance, which was expected to be the substitute of the supersonic Concorde. This project is over due to the theoretical evaluation of the impact of a fleet in the stratosphere and has been replaced by the A380, which is now operating. The largest part is devoted to calculations and observations of the transitions in the infrared range and their applications for the atmosphere based both on effective models (Hamiltonian, symmetry rules, and dipole moments) and ab initio calculations. The complementarities of the two approaches are clearly demonstrated, particularly for the creation of an exhaustive line list consisting of more than 300,000 lines reaching experimental accuracies (from 0.00004 to 0.001 cm-1) for positions and a sub percent for the intensities in the 10 microns region. This contributes to definitively resolving the issue of the observed discrepancies between line intensity data in different spectral regions: between the infrared and ultraviolet ranges, on the one hand, and between 10 and 5 microns on the other hand. The following section is devoted to the application of recent work to improve the knowledge about the behavior of potential function at high energies. A controversial issue related to the shape of the potential function in the transition state range near the dissociation is discussed.

Mass-correlated rotational Raman spectra with high resolution, broad bandwidth, and absolute frequency accuracy.

We present mass-correlated rotational alignment spectroscopy, based on the optical excitation of a coherent rotational quantum wave and the observation of temporal wave interferences in a mass spectrometer. Combined electronic and opto-mechanical delays increased the observation time and energy resolution by an order of magnitude compared with preceding time-domain measurements. Rotational transition frequencies were referenced to an external clock for accurate absolute frequency measurements. Rotational Raman spectra for six naturally occurring carbon disulfide isotopologues were resolved with 3 MHz resolution over a spectral range of 500 GHz. Rotational constants were determined with single-kilohertz accuracy, competitive with state-of-the-art frequency domain measurements.

Application of High-Speed Quantum Cascade Detectors for Mid-Infrared, Broadband, High-Resolution Spectroscopy.

Broadband, high-resolution, heterodyne, mid-infrared absorption spectroscopy was performed with a high-speed quantum cascade (QC) detector. By strictly reducing the device capacitance and inductance via air-bridge wiring and a small mesa structure, a 3-dB frequency response over 20 GHz was obtained for the QC detector, which had a 4.6-µm peak wavelength response. In addition to the high-speed, it exhibited low noise characteristics limited only by Johnson-Nyquist noise, bias-free operation without cooling, and photoresponse linearity over a wide dynamic range. In the detector characterization, the noise-equivalent power was 7.7 × 10-11 W/Hz1/2 at 4.6 µm, and it had good photoresponse linearity up to 250 mW, with respect to the input light power. Broadband and high-accuracy molecular spectroscopy based on heterodyne detection was demonstrated by means of two distributed-feedback 4.5-µm QC lasers. Specifically, several nitrous oxide absorption lines were acquired over a wavelength range of 0.8 cm-1 with the wide-band QC detector.

Sensing Chirality with Rotational Spectroscopy.

Chiroptical spectroscopy techniques for the differentiation of enantiomers in the condensed phase are based on an established paradigm that relies on symmetry breaking using circularly polarized light. We review a novel approach for the study of chiral molecules in the gas phase using broadband rotational spectroscopy, namely microwave three-wave mixing, which is a coherent, nonlinear, and resonant process. This technique can be used to generate a coherent molecular rotational signal that can be detected in a manner similar to that in conventional Fourier transform microwave spectroscopy. The structure (and thermal distribution of conformations), handedness, and enantiomeric excess of gas-phase samples can be determined unambiguously by employing tailored microwave fields. We discuss the theoretical and experimental aspects of the method, the significance of the first demonstrations of the technique for enantiomer differentiation, and the method's rapid advance into a robust choice to study molecular chirality in the gas phase. Very recently, the microwave three-wave mixing approach was extended to enantiomer-selective population transfer, an important step toward spatial enantiomer separation on the fly.

Non-adiabatic effects in the H3+ spectrum.

The effect of non-adiabatic coupling on the computed rovibrational energy levels amounts to about 2 cm-1 for H3+ and must be included in high-accuracy calculations. Different strategies to obtain the corresponding energy shifts are reviewed in the article. A promising way is to introduce effective vibrational reduced masses that depend on the nuclear configuration. A new empirical method that uses the stockholder atoms-in-molecules approach to this effect is presented and applied to H3+. Furthermore, a highly accurate potential energy surface for the D3+ isotopologue, which includes relativistic and leading quantum electrodynamic terms, is constructed and used to analyse the observed rovibrational frequencies for this molecule. Accurate band origins are obtained that improve existing data. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

Cold Snapshot of a Molecular Rotary Motor Captured by High-Resolution Rotational Spectroscopy.

We present the first high-resolution rotational spectrum of an artificial molecular rotary motor. By combining chirped-pulse Fourier transform microwave spectroscopy and supersonic expansions, we captured the vibronic ground-state conformation of a second-generation motor based on chiral, overcrowded alkenes. The rotational constants were accurately determined by fitting more than 200 rotational transitions in the 2-4 GHz frequency range. Evidence for dissociation products allowed for the unambiguous identification and characterization of the isolated motor components. Experiment and complementary quantum-chemical calculations provide accurate geometrical parameters for the C27 H20 molecular motor, the largest molecule investigated by high-resolution microwave spectroscopy to date.

Spectroscopy of Single Dibenzoterrylene Molecules in para-Dichlorobenzene.

We study single dibenzoterrylene (DBT) molecules embedded in 1,4-dichlorobenzene (para-dichlorobenzene, pDCB) at 1.2 K. Due to the relatively low melting point of pDCB (53 °C), this host-guest system can be easily prepared from the molten phase. Narrow linewidths, stable molecular lines and high saturation count rates of single DBT molecules were observed. For this reason, we consider this host-guest system a promising candidate for the study of interactions of single molecules with other small objects such as waveguides or nanoparticles.

On the Additivity of Molecular Fragment Dipole Moments of 5-Substituted Indole Derivatives.

The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations. Based on a natural-bond-orbital analysis, we discuss whether the vector additivity rule can be applied in a given electronic state. From a comparison of the experimental data with ab initio calculations, we deduced that the additivity model does not apply when the flow of electron density from the substituent is opposed to that inside the chromophore.

Reflected Light from Giant Planets in Habitable Zones: Tapping into the Power of the Cross-Correlation Function.

The direct detection of reflected light from exoplanets is an excellent probe for the characterization of their atmospheres. The greatest challenge for this task is the low planet-to-star flux ratio, which even in the most favourable case is of the order of 10-4 in the optical. This ratio decreases even more for planets in their host's habitable zone, typically lower than 10-7. To reach the signal-to-noise level required for such detections, we propose to unleash the power of the Cross Correlation Function in combination with the collecting power of next generation observing facilities. The technique we propose has already yielded positive results by detecting the reflected spectral signature of 51 Pegasi b (see Martins et al. 2015). In this work, we attempted to infer the number of hours required for the detection of several planets in their host's habitable zone using the aforementioned technique from theoretical EELT observations. Our results show that for 5 of the selected planets it should be possible to directly recover their reflected spectral signature.

A journey across dopamine Metabolism: A rotational study of DOPAC.

DOPAC, a relevant scaffold in dopamine metabolism, was probed in the gas phase and interrogated by high-resolution rotational spectroscopy. Herein, three distinct conformers were isolated in a supersonic jet and identified for the first time through an examination of the trend of the rotational constants and the dipole moment selection rules. Additionally, we examined the plausible relaxation pathways of the low-energy conformers of DOPAC, which helped us to claim the indirect detection of two additional conformers, providing conclusive experimental evidence of the flexible nature of this biomolecule. The current investigation sheds some light on the differences between jet-cooled rotational experiments and matrix-isolation infrared spectroscopy.

High-resolution spectroscopy of C2H3D: Line positions and energy structure of the strongly interacting ν10,ν7,ν8,ν4 and ν6 bands.

High resolution infrared spectra of C2H3D were recorded in the region of 550-1950 cm-1 with a Bruker IFS125 HR Fourier transform infrared spectrometers and rotational structures of the five lowest strongly interacting ν10, ν7,ν8,ν4 and ν6 bands were analyzed. The number of about 28000 transitions (4200/6800/5600/5000/6400 for the bands ν10,ν7,ν8,ν4 and ν6) with Jmax = 40 and Kamax = 20 were assigned to these five bands. The weighted fit of 3990 upper energy values obtained from the experimentally recorded transitions was made with a Hamiltonian which takes into account resonance interactions between all studied bands as well as with the sixth ν3 band which was considered in this case as a "dark" one. As the result of analysis, a set of 279 fitted parameters was obtained which reproduces the initial 3990 upper "experimental" ro-vibrational energy values with the drms=1.7×10-4 cm-1; the initial nonsaturated, unblended and not very weak of 28000 assigned transitions are reproduced with the drms=2.2×10-4 cm-1. Ground state parameters of the C2H3D molecule were improved as well.

High resolution spectroscopy of the ν1+ν3 band of the 35ClO2 free radical: Spin-rotation-vibration interactions.

The high resolution spectrum of the ν1+ν3 band of the 35ClO2 free radical was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and theoretically analysed with an improved theoretical basis including the reduced effective spin-rotation Hamiltonian (which takes into account sixth order operators describing spin-rotational interactions) and a newly created computer code ROVDES for the ro-vibrational spectra of open-shell free radicals. About 2600 spin-ro-vibrational transitions with the values Nmax=59 and Kamax=17 (being about 2.4 times higher in comparison with the number of assigned transitions known in the literature) were assigned to the ν1+ν3 band of 35ClO2 and 1049 spin-ro-vibrational energies (produced only from unblended non-saturated and not very weak experimental lines) of the (101) upper vibrational state were obtained. A set of 30 varied parameters of the effective spin-rotation-vibration Hamiltonian of the (101) vibrational state (vibrational energy, 17 rotational and centrifugal distortion parameters and 12 are spin-rotational ones) was determined from the weighted fit of parameters of the effective spin-rotational Hamiltonian in A-reduction and Ir-representation. The obtained set of parameters reproduces the initial 1049 "experimental" upper state energies with the drms=2.5×10-4 cm-1 which is close to the experimental uncertainty of the recorded spectra and is almost 70 times higher in comparison with the analogous reproduction of the same initial upper energies with the use of parameters from (J.Mol.Spectrosc.,158,347-356(1993)).

Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy.

A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements.

Recent Advances in Solid-State Nuclear Magnetic Resonance Spectroscopy.

The sensitivity of nuclear magnetic resonance (NMR) spectroscopy to the local atomic-scale environment offers great potential for the characterization of a diverse range of solid materials. Despite offering more information than its solution-state counterpart, solid-state NMR has not yet achieved a similar level of recognition, owing to the anisotropic interactions that broaden the spectral lines and hinder the extraction of structural information. Here, we describe the methods available to improve the resolution of solid-state NMR spectra and the continuing research in this area. We also highlight areas of exciting new and future development, including recent interest in combining experiment with theoretical calculations, the rise of a range of polarization transfer techniques that provide significant sensitivity enhancements, and the progress of in situ measurements. We demonstrate the detailed information available when studying dynamic and disordered solids and discuss the future applications of solid-state NMR spectroscopy across the chemical sciences.

High-resolution heteronuclear multi-dimensional NMR spectroscopy in magnetic fields with unknown spatial variations.

Heteronuclear NMR spectroscopy is an extremely powerful tool for determining the structures of organic molecules and is of particular significance in the structural analysis of proteins. In order to leverage the method's potential for structural investigations, obtaining high-resolution NMR spectra is essential and this is generally accomplished by using very homogeneous magnetic fields. However, there are several situations where magnetic field distortions and thus line broadening is unavoidable, for example, the samples under investigation may be inherently heterogeneous, and the magnet's homogeneity may be poor. This line broadening can hinder resonance assignment or even render it impossible. We put forth a new class of pulse sequences for obtaining high-resolution heteronuclear spectra in magnetic fields with unknown spatial variations based on distant dipolar field modulations. This strategy's capabilities are demonstrated with the acquisition of high-resolution 2D gHSQC and gHMBC spectra. These sequences' performances are evaluated on the basis of their sensitivities and acquisition efficiencies. Moreover, we show that by encoding and decoding NMR observables spatially, as is done in ultrafast NMR, an extra dimension containing J-coupling information can be obtained without increasing the time necessary to acquire a heteronuclear correlation spectrum. Since the new sequences relax magnetic field homogeneity constraints imposed upon high-resolution NMR, they may be applied in portable NMR sensors and studies of heterogeneous chemical and biological materials.

(1)H NMR spectroscopy for profiling complex carbohydrate mixtures in non-fractionated beer.

A plethora of biological and biotechnological processes involve the enzymatic remodelling of carbohydrates in complex mixtures whose compositions affect both the processes and products. In the current study, we employed high-resolution (1)H NMR spectroscopy for the analysis of cereal-derived carbohydrate mixtures as exemplified on six beer samples of different styles. Structural assignments of more than 50 carbohydrate moieties were obtained using (1)H1-(1)H2 groups as structural reporters. Spectroscopically resolved carbohydrates include more than ''20 different'' small carbohydrates with more than 38 isomeric forms in addition to cereal polysaccharide fragments with suspected organoleptic and prebiotic function. Structural motifs at the cleavage sites of starch, ß-glucan and arabinoxylan fragments were identified, showing different extent and specificity of enzymatic polysaccharide cleavage during the production of different beer samples. Diffusion ordered spectroscopy supplied independent size information for the characterisation and identification of polysaccharide fragments, indicating the presence especially of high molecular weight arabinoxylan fragments in the final beer.