Molecular Spectroscopy Research Articles

Development of Highly Sensitive Techniques of Atomic and Molecular Spectroscopy and Their Application for Cultural Heritage Studies

Development of Highly Sensitive Techniques of Atomic and Molecular Spectroscopy and Their Application for Cultural Heritage Studies

A facile and selective resonance Rayleigh scattering method for trace nitrite using gold nanocluster surface molecularly imprinted polyisopropylacrylamide probe.

A novel gold nanocluster surface molecularly imprinted polyisopropylacrylamide probe (AuNC@MIP) was synthesized for the specific detection of NO2-, using N-isopropylacrylamide (NIPAM) as the functional monomer, gold nanoclusters (AuNC) as the substrate, ethylene glycol dimethacrylate (EGDMA) as the cross-linking agent, and nitrosophenol (NPN) produced from sodium nitrite (NaNO2) and phenol (PN) as the template molecule, N,N-dimethylformamide (DMF) as the solvent, and azobisisobutyronitrile (AIBN) as the initiator. The nanoprobe was characterized using molecular spectroscopy, XPS, TEM, TGA, and zeta potential analysis. The probes revealed a prominent resonance Rayleigh scattering (RRS) peak at 370 nm. Upon addition of NO2-, the RRS intensity at 370 nm decreased due to the RRS energy transfer enhancing. The linear determination range is 0.125-1.50 nmol/L NO2-, with a limit of detection (LOD) of 0.085 nmol/L. The new RRS method was applied to determine NO2- in meat, dairy products, and water samples, with recovery of 96-107% also relative standard deviations (RSDs) of 1.1-8.0%.

Influence of symmetry breaking on the absorption spectrum of crystal violet: from isolated cations at 5 K to room temperature solutions.

We report the resolution of a long-standing puzzle in molecular spectroscopy: the origin of the shoulder in the room temperature solution absorption spectrum of crystal violet (CV) - an archetypal cationic triphenylmethane dye. This was achieved by comparing experimental and theoretical results for CV in solution at room temperature and as an isolated cation in gas-phase at 5 K. The two lowest energy electronically excited states involved in the visible region absorption are degenerate and coupled via a Jahn-Teller (JT) mechanism involving phenyl torsions, making CV particularly sensitive to environmental perturbations. The shoulder is absent in the low-temperature isolated cation spectrum, and vibronic simulations based on time dependent density functional theory (TD-DFT) indicate negligible JT effects under these conditions. Combining vibronic simulations with molecular dynamics, demonstrates that in water and toluene solution at room temperature the shoulder arises mainly from an intermolecular, Jahn-Teller-like symmetry-breaking effect induced by the fluctuating electrostatic potential of the disordered solvent environment, rather than from molecular distortions.

Unlocking the Potential of Isopropanol as an Eco-Friendly Eluent for Large-Scale Fractionation of Fulvic Acids via Preparative Reversed-Phase High-Performance Liquid Chromatography and Multidimensional RP-HPLC: Evaluation of Molecular Diversity and Element Composition.

Humic substances are organic mixtures of extreme complexity, which significantly complicate their analysis by any method. Fractionation into more homogeneous mixtures seems to be almost the only way to overcome these difficulties. Preparative high-performance liquid chromatography (HPLC) provides almost any amounts of substances required for both further fractionation and studies by other methods. For the first time, isopropyl alcohol (IPA) is proposed for these purposes; its advantages are shown by the example of groundwater fulvic acids (FA). IPA is much safer than conventional solvents and elutes the most nonpolar compounds that are nonelutable by methanol and acetonitrile. The isolated fractions differ significantly in their molecular composition, which is confirmed by ultrahigh-resolution mass spectrometry and molecular spectroscopy. Stepwise IPA-gradient HPLC-UV analysis of each preparative fraction demonstrates the possibilities of multidimensional HPLC for FA. The isolated fractions were studied for contents of a broad range of elements, and the relationships between the molecular and trace-element compositions of the fractions were revealed. Our data reveals the existence of numerous and different organometal compounds in FA composition; thus, the proposed approach can be used for a more in-depth study of the mechanisms of element migration in the environment.

High performance SERS boosting by Fabry- Pérot cavities of silica-gold-silicon multilayers

Surface-enhanced Raman scattering (SERS), an advanced technique for molecular spectroscopy, relies heavily on the preparation of SERS active materials that can significantly enhance the Raman scattering signals for highly sensitive detection of trace molecules. Traditionally, SERS measurements are performed on silicon or silica substrates, the SERS performance is determined by the structure of SERS materials. Here, we show that the SERS signal can be amplified and modulated using Fabry-Pérot (F-P) cavities made of silica-silicon (SiO2-Si) or silica-gold-silicon (SiO2-Au-Si) multilayers as substrates. Periodic SERS signal variations as SiO2 thickness increases are observed, exhibiting optimal enhancement with the SiO2 thickness of 250 nm due to the optical interference in the cavity. Although the signal enhancement by optical interference is weaker than that by plasmonic resonance, additional signal amplification is essential for highly sensitive SERS materials. Moreover, we applied this strategy to detect thiram in bean sprout extracts, demonstrating that the detection sensitivity is two orders of magnitude higher than that using Si substrates. The utilization of the pseudo-internal standard intensity calibration method facilitates the quantitative analysis of thiram concentrations. Our results provide a promising approach for further amplification of SERS signals with great potential for practical applications.

Elucidating the isotope effect in the Morse approximation of the ground state electronic term of hydrogen molecules nH2, n = 1 ÷ 7. Showcasing the Herzberg anomaly and anharmonicity

The Morse function is the simplest anharmonic approximation of the potential of a diatomic molecule, for which the vibrational Schrödinger equation could be solved almost precisely. Despite its crudeness, the Morse function has been widely used in solving various problems in molecular spectroscopy. In recent years, special attention was paid to the existence of two Morse approximations for the electronic terms U(r) of diatomic molecules, M1(r) and M2(r), which differ by the selection of primary fitting parameters and satisfactorily reproduce different parts of U(r). Some fine features of simple terms U(r), whose form does not differ much from the Morse function, could be highlighted by considering difference functions U(r) − M(r). The set of vibrational levels G(υ), predicted by Morse approximation, can be conveniently characterized by the difference functions Δ1G(υ) and Δ2G(υ), which are, respectively, the energies of vibrational quanta and the rates of their change. The function Δ2G(υ) can be considered as a generalization of the anharmonicity constant, determined experimentally by the position of levels υ = 0,1,2. Finally, analysing the anharmonicity, it is useful to compare the results obtained for various isotopologues, for which U(r) is the same, but the density of vibrational levels is different. The maximal range of isotope effects is expected for hydrogen, which has seven known isotopes, including extremely short-lived ones. In this work, the influence of the reduced mass on the results of the approximation of the electronic ground state potential U(r) by the Morse function is studied for seven isotopologues of hydrogen molecule nH2 (n = 1–7). For each isotopologue, alternative approximations M1(r) and M2(r) are considered. The systematic deviation of M1(r) from U(r) increases with r, reaching 1700–2770 cm−1 (for 7H2–1H2) in the region of the asymptote. The systematic deviation of M2(r) from U(r) decreases at larger distances: it is dome-shaped with a maximum of ca. 1500 cm−1 at r ∼ 2 Å, after which it falls to zero. The M2(r) curves for different isotopologues diverge by less than 20 cm−1. The U(r) − M(r) functions are used to analyse the so-called “Herzberg anomaly” in the region where M1(r) and M2(r) intersect U(r). For example, at around r = 1.08 Å the U(r) − M2(r) function shows anomalous negative values ranging from −125 cm−1 (for 1H2) to −142 cm−1 (for 7H2).

Monolithic dispersion engineered mid-infrared quantum cascade laser frequency comb

The high-power quantum cascade laser (QCL) frequency comb capable of room temperature operation is of great interest to high-precision measurement and low-noise molecular spectroscopy. While a significant amount of research is devoted to the longwave spectral range, shortwave 3–5 μm QCL combs are still relatively underdeveloped due to the excessive material dispersion. In this work, we propose a monolithic integrated multimode waveguide scheme for effective dispersion engineering and high-power-efficiency operation. Over watt-level output power at room temperature with a wall plug efficiency of 7% and robust dispersion reduction is achieved from a quantum cascade laser frequency comb at a wavelength approximately 4.6 μm. Narrow beatnote linewidth less than 1 kHz and clear dual-comb multiheterodyne comb lines manifest the coherent phase relation among the comb modes which is crucial to fast molecular spectroscopy. This monolithic dispersion engineered waveguide design is also compatible to an efficient active–passive optical coupling scheme and would open up a new research playground for ring comb and on-chip dual-comb spectroscopy.

Optical frequency synthesizer for wide range frequency scan and its application to high-resolution molecular spectroscopy

Optical frequency synthesizer for wide range frequency scan and its application to high-resolution molecular spectroscopy

Critical analysis of analytical techniques developed for statins in biological fluids, environmental and fermentation samples.

Statins are the most prescribed drug for regulating the high cholesterol level in the blood, which can lead to severe complications, such as cardiovascular diseases and other health complications. A wide range of analytical techniques have been employed for the quantification of statins from various origins, including fermentation derived (lovastatin, pravastatin, and compactin), semi-synthetic (simvastatin), and synthetic (atorvastatin, rosuvastatin, and fluvastatin) routes. The presence of more than one structural form and structural analogue generated in the biosynthesis pathway, as well as reaction intermediates and macromolecules in the clinical sample, complicates the quantification of statins. Furthermore, significant concentrations of statins in environmental samples pose serious health and ecology hazards, and estimating statins in those diluted samples is extremely difficult. On the other hand, the: cost, accurate estimation of the desired one from other structural forms, sample complexity, time, limits of detection and quantification, were major criteria distinguishing the usability of each technique. As a result, the current manuscript focuses on analytical techniques such as molecular spectroscopy (normal and derivatives UV-Visible spectrophotometer), chromatography (TLC, HP-TLC, HPLC, GC, swing column, micellar, and supercritical fluid), mass spectroscopy (HPLC-MS/MS and GC-MS/MS), sequential flow injection, capillary electrophoresis, and cyclic voltammetry, as well as their: optimal operating conditions, limits of detection and quantification, advancements, and limitations. Furthermore, various online and offline sample preparations (precipitation, solid phase extraction, liquid-liquid extraction, and micellar extraction) have been highlighted as an essential pretreatment technique to avoid the interference caused by structural analogues and other macromolecules. The greener and more sustainable concepts used in analytical approaches for the quantification statins are also highlighted with current advancements.

Synthesis of newly designed hydrazones, in vitro and in silico studies, and structure-activity relationship

Herein, new N'-(substituted benzylidene)-3,5-dihydroxybenzohydrazide (1–13) series were synthesized, and their antioxidant, anticholinesterase, anti-tyrosinase, anti-urease, and antidiabetic activities were investigated together with in silico studies. The synthesized derivates were characterized using molecular spectroscopy, and the structure-activity relationships (SAR) were discussed for all tested biological assays. According to activity results, compound 3 exhibited excellent antioxidant activity in all tests, while compound 1 demonstrated the best acetylcholinesterase (AChE) inhibitory and butyrylcholinesterase (BChE) inhibitory activities. On the other hand, compound 11 showed excellent tyrosinase inhibitory (IC50:3.02±0.10 mM) and urease inhibitory (IC50:9.21±0.27 µM) activity. Moreover, among the synthesized compounds, compound 6 was detected as the best antidiabetic compound by inhibiting α-amylase (IC50:30.68±0.94 µM) and α-glycosidase (IC50:41.35±0.03 µM) enzymes, which were related with the antidiabetic activity. Molecular docking analysis confirmed AChE, BChE, tyrosinase, urease, α-amylase, and α-glucosidase inhibitory activities. In line with the findings obtained from in vitro bioactivity results and molecular docking analysis, hydrazone compounds are a suitable class of organic compounds for developing acetylcholinesterase, butyrylcholinesterase, urease, α-amylase, and α-glucosidase inhibitors.

Inhalable Advanced Co-Spray Dried Microparticles/Nanoparticles of a Novel RhoA/Rho Kinase Inhibitor with Lung Surfactant Biomimetic Phospholipids for Targeted Lung Delivery.

Co-spray dried inhalable powder formulations of fasudil monohydrochloride salt (FMCS) and inhalable lung surfactant-based nanocarriers composed of synthetic phospholipids, zwitterionic DPPC (1,2-palmitoyl-sn-glycero-3-phosphocholine) and anionic DPPG (1,2-dipalmitoyl-sn-glycero-3-[phosphor-rac-1-glycerol]) sodium salt, were designed and optimized using organic solution advanced spray drying. FMCS can potentially be used for the treatment of various complex pulmonary diseases with this current work focusing on pulmonary arterial hypertension. Comprehensive physicochemical characterization, electron and optical microscopy imaging, thermal analysis, molecular fingerprinting spectroscopy, in vitro aerosol dispersion performance with human dry powder inhaler (DPI) devices, in vitro membrane permeation and drug release, and in vitro human cellular studies were conducted. Well-defined, small, and smooth nanoparticles/microparticles in the solid state were engineered at different molar ratios of FMCS/DPPC/DPPG (25:75, 50:50, and 75:25) and successfully produced as inhalable powders having the properties necessary for targeted pulmonary delivery as dry powder inhalers. In vitro aerosol performance demonstrated excellent aerosol dispersion with different DPI devices. The phospholipid bilayer biophysical properties were confirmed and retained following cospray drying. Sustained release of fasudil drug and in vitro biocompatibility were demonstrated on human lung cells from different airway regions.

Pressure control of tritiated hydrogen isotopologues in hermetically sealed vessels by non-evaporable getters for sub-Doppler-resolution spectroscopy

Small molecules serve as valuable benchmarks for testing quantum chemical theories. Ultra-high-resolution spectroscopy currently offers the capability of measuring molecular hydrogen energy levels with a relative accuracy on the order of 10-10. Expanding such investigations to encompass different isotopologues of molecular hydrogen has emerged as a promising avenue for examining mass-dependent contributions to the full description of molecular structure in the framework of relativistic quantum electrodynamics. However, the delicate nature of handling radioactive tritium in a high-resolution spectroscopy environment poses significant technological challenges, thereby limiting the extension of these studies to include T2, DT and HT isotopologues. In this work, we present the experimental setup of the very sensitive, Doppler-free technique of Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS), used to measure rovibrational transitions in the HT molecule. The NICE-OHMS measurements were performed in a closed cavity system without connection to an actively pumped vacuum system. For this reason, a new method for tritium storage and pressure regulation within 0.05–1Pa based on a temperature-controlled mini-getter system is employed using less activity than the tritium exemption limit (1GBq). Non-Evaporable Getters of the type SAES St171 were used for this purpose exploiting their property that hydrogen is released upon heating, while other gases remain being pumped. Prior to the NICE-OHMS experiment, the reversible sorption properties of the getter for hydrogen isotopes were investigated. We show measurements of the equilibrium (hydrogen) pressure for all three pure isotopes and for a H2:HT:T2 mixture (with H:T = 1:1) as a function of temperature for a system of defined volume and amount of gas. For the read-out of the temperature, a method using the resistance of the getter in combination with a pyrometric calibration has been implemented. We discuss the experiences from practical use of the tritium getter and show results obtained with the NICE-OHMS setup leading to frequency calibration of near-infrared transitions in HT at an accuracy, surpassing previous studies by nearly three orders of magnitude.

Enhancing forensic blood detection using hyperspectral imaging and advanced preprocessing techniques

Bloodstains are pivotal in forensic investigations as they can provide crucial DNA information about individuals involved in a crime. Traditional methods for bloodstain detection, including chemical tests and forensic lights, have limitations such as non-specificity to human blood and susceptibility to false positives. In forensic blood detection, molecular spectroscopy is crucial for identifying the unique spectral fingerprints of blood, which arise from its molecular composition. Hyperspectral imaging (HSI) leverages this principle by capturing a wide spectrum of light for each pixel in an image, allowing for the detailed analysis of various substances. HSI has emerged as a promising alternative, offering non-contact, rapid, and cost-effective detection of bloodstains by analyzing the visible and near-infrared electromagnetic spectrum. This study explores the application of HSI for blood detection, addressing challenges such as spectral mixing, time-related changes in bloodstain spectra, and data complexity. The study introduces a novel framework to optimize HSI data, enhancing the accuracy and efficiency of bloodstain classification, called the Fast Extraction (FE) framework. It includes two stages. The main method in the first one is the Enhancing Transformation Reduction (ETR) method to reduce the dimension and complexity of the HSI. The second stage contains a compatible classification model to enhance feature extraction and classification. Our approach is validated using the HyperBlood datasets and many evaluation methods, demonstrating superior performance compared to state-of-the-art deep learning models. It provides high accuracy (97%–100 %) for all HSIs, overcoming various difficulties and blood collection times.

Innovative use of lipid mesophase dispersions for bisphenol A sequestration in water

HypothesisMesophase dispersions are promising colloids for removing micropollutants from water. We hypothesized that the complex internal nanostructure and tunable lipid/water interface amounts play a crucial role in absorbed quantities. Modifications in interfacial organization within the particles while trapping the micropollutant is assumed. ExperimentsWe formulated stable monolinolein-based dispersions with four types of mesophases (bicontinuous and micellar cubic, hexagonal, and fluid isotropic L2) by varying dodecane contents. The absorption of bisphenol A by these dispersions from water was monitored using molecular spectroscopy. At equilibrium, absorbed quantities by mesophase dispersions were compared to unstructured dodecane/water miniemulsions for two bisphenol concentrations. Structural changes during bisphenol incorporation were identified using small-angle X-ray scattering. FindingsLipid mesophase particles of submicron size showed greater bisphenol incorporation than dodecane/water miniemulsions, with cubosomes being most effective ones, absorbing twice as much as unstructured emulsions. Higher absorption levels are observed for more complex nanostructures with increased lipid/dodecane ratios. The incorporation of bisphenol affected the curvature of internal interfaces, potentially causing phase transitions and indicating that bisphenol settles at interfaces. Similar absorption levels in identical mesophases suggest a strong correlation between nano-structure and absorbed quantities.

The W2024 database of the water isotopologue H216O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\rm{H}}}_{2}^{\\,16}{\\rm{O}}$$\\end{document}

The rovibrational spectrum of the water molecule is the crown jewel of high-resolution molecular spectroscopy. While its significance in numerous scientific and engineering applications and the challenges behind its interpretation have been well known, the extensive experimental analysis performed for this molecule, from the microwave to the ultraviolet, is admirable. To determine empirical energy levels for H216O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\bf{H}}}_{{\\bf{2}}}^{\\,{\\bf{16}}}{\\bf{O}}$$\\end{document}, this study utilizes an improved version of the MARVEL (Measured Active Rotational-Vibrational Energy Levels) scheme, which now takes into account multiplet constraints and first-principles energy-level splittings. This analysis delivers 19027 empirical energy values, with individual uncertainties and confidence intervals, utilizing 309 290 transition wavenumbers collected from 189 (mostly experimental) data sources. Relying on these empirical, as well as some computed, energies and first-principles intensities, an extensive composite line list, named CW2024, has been assembled. The CW2024 dataset is compared to lines in the canonical HITRAN 2020 spectroscopic database, providing guidance for future experimental investigations.

Tracing the Background‐Suppressed Vibrational Decay Time of a Molecular Monolayer with Time‐Resolved Surface‐Enhanced Broadband Coherent Anti‐Stokes Raman Scattering

AbstractThe sensitivity of molecular spectroscopy based on surface‐enhanced coherent anti‐Stokes Raman scattering (SECARS) is limited by the spectrally overlapping background from nonresonant four‐wave mixing (FWM). While the SECARS signal is mediated by the molecular vibrational eigenstates and exhibits long lifetime (a few picoseconds), the FWM background stems from the instantaneous electronic polarization and decays rapidly with the vanishment of excitation. Therefore, CARS and FWM can be separated by time‐resolved CARS (trCARS) using ultrashort pulsed lasers. The broad spectral bandwidth also enables broadband CARS (BCARS) for simultaneous identification of multiple vibrational signatures. This work combines trCARS and BCARS with an optimized plasmonic system to demonstrate time‐resolved surface‐enhanced BCARS) and show its capability in obtaining background‐suppressed broadband vibrational spectra from a monolayer of 4‐Aminothiophenol (4‐ATP) molecules self‐assembled on a gold grating. The vibrational dephasing time of the ring‐breathing mode for the 4‐ATP monolayer on the gold grating (≈1.00 ± 0.17 ps) is significantly shortened compared to that for 4‐ATP powder on a glass substrate (2.10 ± 0.05 ps). This work presents an effective method to suppress FWM background and investigate the vibrational dynamics of molecules in the vicinity of plasmonic nanostructures.

Exploring flavonoids as potential inhibitors for Enterococcus faecium nicotinate nucleotide adenylyltransferase: An integration of in silico with empirical studies

Nicotinate nucleotide adenylyltransferase (NNAT) emerges as a promising target for drug development, given its pivotal role in the nicotinate nucleotide biosynthesis pathway crucial for bacterial survival. Using computational modelling and fluorescence methods, this study screened a library of 1427 compounds from MedChemExpress as potential inhibitors against Enterococcus faecium NNAT (EfNNAT). We employed Maestro's Glide HTVS, SP, and XP docking protocols to identify compounds with high binding affinity. The screening utilised two models of the EfNNAT crystal structure: energy-minimised and 100-ns MD-simulated model, hypothesising conformational change that may influence ligand selectivity in the HTVS study. Our findings revealed variations between the minimised versus MD-simulated models, impacting ligand selectivity by each model post-HTVS. However, quercetin 3-O-beta-d-glucose-7-O-beta-d-gentiobioside (QGG) appeared to be the top inhibitor selected by both models after more rigorous docking using Maestro-implemented SP and XP. A 500-ns all-atom MD simulation of the EfNNAT:ligand complex revealed that the compound interacts mainly through hydrogen bonding and water bridges. Validation of the in-silico studies via molecular spectroscopy confirmed QGG's binding to EfNNAT by displacing the fluorescent probes from the protein binding site. Although the binding demonstrated minimal impact on the thermal stability of EfNNAT as deduced from the thermal shift assay, ITC showed that QGG exhibits moderate binding affinity for EfNNAT, with the interaction being spontaneous and thermodynamically favourable. Insights gleaned from this study offer a mechanistic basis that could be leveraged to develop new leads. Expansion of the compound library holds promise for identifying inhibitors with enhanced affinity for EfNNAT.

Forward osmosis membrane with lightweight functionalised multiwall carbon nanotube nanofillers

ABSTRACT Thin-film nanocomposite (TFN) membranes with a polyamide (PA) active layer modified with carbon nanotubes (CNTs) hold promise for water desalination and wastewater reuse via forward osmosis (FO). We hypothesise that modifying the PA active layer with hydroxyl-functionalised multi-wall carbon nanotubes (f-MWCNTs) will enhance the water flux of the FO membrane while maximising salt rejection. TFN membranes were modified using in situ interfacial polymerisation, with varying f-MWCNT mass content to minimise agglomeration. These modified FO membranes are designated as CTFN-x, where x represents the mass content of f-MWCNTs, ranging from 0.001%, CTFN-1 to 0.008%, CTFN-8 (w/v). The surface properties of CTFN-x were characterised using electron microscopy, atomic force microscopy, and molecular spectroscopy. IR spectroscopic data confirm the successful adherence of f-MWCNTs as a bridging agent between the 1,3-phenylenediamine (MPD) and trimesoyl chloride (TMC) polymers, preserving FO membrane integrity. The CTFN-4 FO membrane shows the highest water flux (29 LMH) and the lowest reverse salt flux (2.90 gHM), attributed to preferential water flow channels in the f-MWCNTs. The integration of f-MWCNTs into the active layer improved water flux, reduced reverse salt flux, and enhanced the antifouling properties of FO membranes.

Time Resolved Quantum Tomography in Molecular Spectroscopy by the Maximal Entropy Approach.

Attosecond science offers unprecedented precision in probing the initial moments of chemical reactions, revealing the dynamics of molecular electrons that shape reaction pathways. A fundamental question emerges: what role, if any, do quantum coherences between molecular electron states play in photochemical reactions? Answering this question necessitates quantum tomography─the determination of the electronic density matrix from experimental data, where the off-diagonal elements represent these coherences. The Maximal Entropy (MaxEnt) based Quantum State Tomography (QST) approach offers unique advantages in studying molecular dynamics, particularly with partial tomographic data. Here, we explore the application of MaxEnt-based QST on photoexcited ammonia, necessitating the operator form of observables specific to the performed measurements. We present two methodologies for constructing these operators: one leveraging Molecular Angular Distribution Moments (MADMs) which accurately capture the orientation-dependent vibronic dynamics of molecules and another utilizing Angular Momentum Coherence Operators to construct measurement operators for the full rovibronic density matrix in the symmetric top basis. A key revelation of our study is the direct link between Lagrange multipliers in the MaxEnt formalism and the unique set of MADMs. Additionally, we visualize the electron density within the molecular frame, demonstrating charge migration across the molecule. Furthermore, we achieve a groundbreaking milestone by constructing, for the first time, the entanglement entropy of the electronic subsystem─a metric that was previously inaccessible. The entropy vividly reveals and quantifies the effects of coupling between the excited electron and nuclear degrees of freedom. Consequently, our findings open new avenues for research in ultrafast molecular spectroscopy within the broader domain of quantum information science, offering profound implications for the study of molecular systems under excitation using quantum tomographic schemes.

Theoretical infrared spectroscopy of protonated methane isotopologues.

The vibrational spectroscopy of protonated methane and its mixed hydrogen/deuterium isotopologues remains a challenge to both experimental and computational spectroscopy due to the iconic floppiness of CH5+. Here, we compute the finite-temperature broadband infrared spectra of CH5+ and all its isotopologues, i.e. CHnD5-n+ up to CD5+, from path integral molecular dynamics in conjunction with interactions and dipoles computed consistently at CCSD(T) coupled cluster accuracy. The potential energy and dipole moment surfaces have been accurately represented in full dimensionality in terms of high-dimensional neural networks. The resulting computational efficiency allows us to establish CCSD(T) accuracy at the level of converged path integral simulations. For all six isotopologues, the computed broadband spectra compare very favorably to the available experimental broadband spectra obtained from laser induced reactions action vibrational spectroscopy. The current approach is found to consistently and significantly improve on previous calculations of these broadband vibrational spectra and defines the new cutting-edge for what has been dubbed the "enfant terrible" of molecular spectroscopy in view of its pronounced large-amplitude motion that involves all intramolecular degrees of freedom.