Molecular Vibrational Transitions Research Articles

Quantum nature of reactivity modification in vibrational polariton chemistry.

In this work, we present a mixed quantum-classical open quantum system dynamics method for studying rate modifications of ground-state chemical reactions in an optical cavity under vibrational strong-coupling conditions. In this approach, the cavity radiation mode is treated classically with a mean-field nuclear force averaging over the remaining degrees of freedom, both within the system and the environment, which are handled quantum mechanically within the hierarchical equations of motion framework. Using this approach, we conduct a comparative analysis by juxtaposing the mixed quantum-classical results with fully quantum-mechanical simulations. After eliminating spurious peaks that can occur when not using the rigorous definition of the rate constant, we confirm the crucial role of the quantum nature of the cavity radiation mode in reproducing the resonant peak observed in the cavity frequency-dependent rate profile. In other words, it appears necessary to explicitly consider the quantized photonic states in studying reactivity modification in vibrational polariton chemistry (at least for the model systems studied in this work), as these phenomena stem from cavity-induced reaction pathways involving resonant energy exchanges between photons and molecular vibrational transitions.

Computational simulation on the study of Tacrolimus and its improved dermal retention using Poly(Ԑ-caprolactone) nanocapsules

Tacrolimus (TAC) is a drug from natural origin that can be used for topical application to control autoimmune skin diseases such as atopic dermatitis, psoriasis, and vitiligo. Computational simulation based on quantum mechanics theory by solving Schrödinger Equation for n-body problem may allow the theoretical calculation of drug geometry, charge distribution and dipole moment, electronic levels and molecular orbitals, electronic transitions, and vibrational transitions. Additionally, the development of novel nanotechnology-based delivery systems containing TAC can be an approach for reducing the dose applied topically, increasing dermal retention, and reducing the reported side effects due to the controlled release pattern. Firstly, this paper was devoted to obtaining the molecular, electronic, and vibrational data for TAC by using five semi-empirical (SE) methods and one Density Functional Theory (DFT) method in order to expand the knowledge about the drug properties by computational simulation. Then, this study was carried out to prepare TAC-loaded poly(ԑ-caprolactone) nanocapsules by interfacial polymer deposition following solvent displacement and investigate the in vitro drug permeation using the Franz diffusion cell and the photoacoustic spectroscopy. Computational simulations were compared in the three schemes SE/SE, SE/DFT, and DFT/DFT, where the first method represented the procedure used for geometry optimization and the second one was performed to extract electronic and vibrational properties. Computational data showed correspondence with TAC geometry description and electronic properties, with few differences in HOMO – LUMO gap (Δ) and dipole values. The SE/DFT and DFT/DFT methods presented a better drug description for the UV–Vis, Infrared, and Raman spectra with low deviation from experimental values. Franz cell model demonstrated that TAC was more delivered across the Strat-M® membrane from the solution than the drug-loaded poly(ԑ-caprolactone) nanocapsules. Photoacoustic spectroscopy assay revealed that these nanocapsules remained more retained into the Strat-M® membranes, which is desirable for the topical application.

Synthesis, characterization, theoretical calculations of novel benzoic acid based azo molecules and their use in effective extraction of Hg(II) ions from aqueous medium

In this study, two series of benzoic acid derivative azo compounds were synthesized using coupling reaction and characterized by various spectroscopic techniques. By using o-, m-, p-chloroaniline and o-, m-, p-nitroaniline as starting materials, the effects of the directing groups on the color intensity of azo dyes were investigated. It was concluded that the nitro group increased both the reaction efficiency and the color intensity. Optimized molecular structures, vibrational and electronic transition spectra, NMR chemical shift values, frontier molecular orbitals and MEP diagrams of each molecule were calculated using the 6-311G(d,p) basis set. All calculations were performed and compared with both Density Functional Theory (DFT) and Hartree-Fock (HF) methods. Experimental and theoretical results were found to be quite compatible with each other. The extraction capabilities of all synthesized azo derivatives were investigated using various transition metal picrates such as Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+ cations. Solvent extraction studies of azo derivatives revealed that all compounds showed strong binding ability against Cu2+ and especially Hg2+ ions and were able to remove the Hg2+ cation from aqueous medium at a high rate (97.3%).

Vibration-Cavity Polariton Chemistry and Dynamics.

Molecular polaritons result from light-matter coupling between optical resonances and molecular electronic or vibrational transitions. When the coupling is strong enough, new hybridized states with mixed photon-material character are observed spectroscopically, with resonances shifted above and below the uncoupled frequency. These new modes have unique optical properties and can be exploited to promote or inhibit physical and chemical processes. One remarkable result is that vibrational strong coupling to cavities can alter reaction rates and product branching ratios with no optical excitation whatsoever. In this work we review the ability of vibration-cavity polaritons to modify chemical and physical processes including chemical reactivity, as well as steady-state and transient spectroscopy. We discuss the larger context of these works and highlight their most important contributions and implications. Our goal is to provide insight for systematically manipulating molecular polaritons in photonic and chemical applications.

Boosting Self-interaction of Molecular Vibrations under Ultrastrong Coupling Condition.

In this letter, we investigated the modification of the oscillator strength of an asymmetric stretching band of CS2 by strong coupling to an infrared cavity photon. This is achieved by placing liquid CS2 in a Fabry-Perot resonator and tuning the cavity mode position to match the molecular vibrational transition. Ultrastrong coupling leads to an increase in the effective oscillator strength of the asymmetric stretching band of CS2. We proved this experimentally by taking the area ratio of the asymmetric stretching and combination bands by selectively coupling the former. A nonlinear increase in the oscillator strength of the asymmetric stretching band is observed upon varying the coupling strength. This is explained by a quantum mechanical model that predicts quadratic behavior under ultrastrong coupling conditions. These findings will set up a new paradigm for understanding chemical reaction modifications by vacuum field coupling.

Experimental methods in chemical engineering: Raman spectroscopy

AbstractWhen photons impinge on a substrate, most scatter with the same frequency (elastic scattering or Rayleigh dispersion) and only 10−7 scatter with a different energy (inelastic scattering). This inelastic interaction (Raman scattering) exchanges energy in the region of molecular vibrational transitions for crystalline and amorphous materials. Raman bands in a spectra represent vibrational transitions, like infrared, however the selection rules are different. Typically, the vibrations that are intense in Raman are weak in infrared and vice versa. A remarkable feature of the Raman effect is that it is highly sensitive to nanocrystals, even below 4 nm, which are too small to generate XRD patterns. Plasmonic enhancement, like surface‐enhanced Raman spectroscopy (SERS) boost the Raman signal by 104, providing single‐molecule detection capability. Glass, quartz, and sapphire are transparent to Raman effect (depending on the energy of the incident excitation radiation), which makes it ideal to examine materials under reaction conditions (in‐situ cells and operando reactors that operate over a broad range of temperature, pressures, and environments). Raman spectroscopy emerged in the 1930s; however, infrared spectrometry displaced it. With the advent of powerful lasers in the 1970s, more researchers began to apply Raman routinely. In 2019, the Web of Science indexed 20 400 articles mentioning Raman against 50 000 articles mentioning infrared. Chemical engineers apply Raman less frequently than in material science, physical chemistry, and applied physics, with 887 articles vs 6250, 3700, and 3510 for the other disciplines. A bibliometric analysis identified four research clusters centred on thin films and optics, graphene and nanocomposites, nanoparticles and SERS, and photocatalyst.

Investigation of buffer gas trapping of positrons

A study of positron capture in a two-(pressure) stage buffer gas accumulation apparatus is presented for a variety of species, including some molecules which are known to be either efficient for positron trapping, or are frequently used to cool the particles when held in these devices. Absolute accumulation efficiencies are reported for all species. A detailed optimisation procedure, which has identified the main processes responsible for positron capture and loss in the trap, has been deployed to explore accumulation efficiency as the gas pressure and the electrostatic well depth in the trap are systematically varied. Accumulation exploiting energy loss via molecular vibrational transitions has been observed for the first time for a number of gases, though at much lower efficiency than achieved using electronic excitation processes.

Preparation and Characterization of PVA-Co-PE Drug-Loaded Nanofiber Membrane by Electrospinning Technology.

A new transdermal drug delivery system of nanofiber membrane with good biocompatibility and high drug loading was developed by electrospinning technology in this study. Using vinyl alcohol-co-ethylene (PVA-co-PE) polymer as a spinning matrix and non-steroidal anti-inflammatory drug (NSAID) sulindac (SUL) as a model drug, the SUL@PVA-co-PE nanofiber membrane was prepared and characterized systematically. The morphology, molecular vibrational transitions, thermogravimetric attributes, and in vitro drug release and transdermal characteristics of drug-loaded nanofiber membranes were analyzed. The results indicated that the surface of PVA-co-PE nanofibers was uniform and smooth with the diameter ranged from 461 to 696nm. Notably in vitro simulation experiments demonstrated that SUL@PVA-co-PE nanofiber membrane could provide a continuous drug release to reach the effective concentration of the drug, and exhibited significantly higher cumulative drug permeability compared to commercially available patches, Taken together, PVA-co-PE nanofiber membranes exhibited the characteristics of high drug loading and stability, and represented the potential to be utilized as a new transdermal drug delivery carrier with pronounced development prospect.

Critical Test of the Interaction of Surface Plasmon Resonances with Molecular Vibrational Transitions.

We determine the infrared absorption spectra of a gas due to evanescent plasmonic electromagnetic fields in a system where surface interactions (physisorption and chemisorption) are demonstrably negligible. The plasmonic host material, the degenerate semiconductor CdO:Dy, has high mobility (366-450 cm2/(V s)) and carrier density ((0.6-3.5) × 1020 cm-3), and therefore supports low-loss surface plasmon resonances in the mid-IR. This high-mobility layer gives the highest resolution observed in a plasmonic conducting material in the infrared, higher than that of gold and rivaling that of silver. The high resolution permits a new understanding of the nature of the interaction of emerging fields with molecular transitions. Using different carrier concentrations, the resonance condition of the surface plasmon polariton (SPP) frequency (ωSPP) and N2O vibrational absorption spectral frequency (ωN2O) can be controlled, thereby allowing a critical test of field-molecule interactions. Experiment and theory both indicate a dispersive N2O line shape for ωSPP < ωN2O, an absorptive line shape for ωSPP < ωN2O, and an abrupt change between the two when the resonance condition ωSPP < ωN2O is reached. A first-order expansion of the Airy equation describes this behavior analytically. The SPP surface enhancement is 6.8 ± 0.5 on-resonance, lower than enhancements observed in other systems, but in agreement with recent quantitative reports of surface enhanced infrared reflection absorption spectroscopy (SEIRA). Our results show that interactions of infrared SPPs with molecular vibrations are in the weak coupling limit, and that enhancements comparable those reported for noble metals can be achieved.

Broadband cw-terahertz spectroscopy for characterizing reactive plasmas

Terahertz spectroscopy is seeing increasing use in analytical chemistry because of its ability to access ground state molecular rotational and vibrational transitions. Experiments reported on the use of THz spectroscopy to the studies of low pressure plasmas have focused on the use of pulsed sources, which have limited spectral resolution. These are suitable in the characterization of plasma parameters such as electron density, but somewhat inadequate in the study of molecular absorption spectra. The recent commercial availability of continuous THz sources with much higher spectral resolution has afforded the detailed probing of molecular absorption features but they have not yet been exploited in studies of low pressure plasma chemistry. One of the major benefits of continuous-wave THz spectroscopy (cw-TS) compared to optical and infrared methods is its applicability to the study of both plasma chemistry as well as parameters, i.e. electron density and collision frequency. In this article, we provide first insights into the use of cw-TS as a plasma diagnostic, and demonstrate the opportunities and challenges by example measurements in a low-pressure argon-methanol radio frequency inductively coupled plasma in which we estimate both the plasma-induced dissociation in the precursor methanol concentration, as well as the electron density and momentum scattering collision frequency.

Non-destructive Monitoring of Molecular Vibrational Transitions

Transition frequency measurement by monitoring a phase shift requires no cycling transition and appears to be applicable to molecular vibrational transitions. We estimated the attainable signal-to-...

Novel Nanostructures and Materials for Strong Light–Matter Interactions

Quantum mechanical interactions between electromagnetic radiation and matter underlie a broad spectrum of optical phenomena. Strong light-matter interactions result in the well-known vacuum Rabi splitting and emergence of new polaritonic eigenmodes of the coupled system. Thanks to recent progress in nanofabrication, observation of strong coupling has become possible in a great variety of optical nanostructures. Here, we review recently studied and emerging materials for realization of strong light–matter interactions. We present general theoretical formalism describing strong coupling and give an overview of various photonic structures and materials allowing for realization of this regime, including plasmonic and dielectric nanoantennas, novel two-dimensional materials, carbon nanotubes, and molecular vibrational transitions. In addition, we discuss practical applications that can benefit from these effects and give an outlook on unsettled questions that remain open for future research.

Accuracy estimation of the O216+ transition frequencies targeting the search for the variation in the proton-electron mass ratio

The precise measurement of molecular vibrational transition frequencies is useful in the search for variation in the proton-to-electron mass ratio {\mu}. Homonuclear diatomic molecules are particularly advantageous for precise measurement because of the small Stark shift. This paper discusses the Stark and Zeeman shifts in the 16O2+ vibrational transition frequencies.To search for the variation {\mu}(<10-17/yr), the X2{\Pi}1/2(v,J)=(0,1/2)-(v',1/2)(v'>1)in transition frequencies are much more advantageous than the transition frequencies between the X2{\Pi}1/2 v=21 and a4{\Pi}1/2 v=0 states, whose sensitivity to the variation in {\mu} is high because of the accidental degeneracy.

High sensitivity to variation in the proton-to-electron mass ratio inO2+

Molecular vibrational transitions are prime candidates for model-independent searches for variation of the proton-to-electron mass ratio. Searches for present-day variation achieve highest sensitivity with deep molecular potentials. We identify several high-sensitivity transitions in the deeply bound ${\rm O}_2^+$ molecular ion. These transitions are electric-dipole forbidden and thus have narrow linewidths. The most sensitive transitions take advantage of an accidental degeneracy between vibrational states in different electronic potentials. We suggest experimentally feasible routes to a measurement with uncertainty exceeding current limits on present-day variation in $m_p/m_e$.

Electronic Nose for Recognition of Volatile Vapor Mixtures Using a Nanopore-Enhanced Opto-Calorimetric Spectroscopy.

An electronic nose (e-nose) for identification and quantification of volatile organic compounds (VOCs) vapor mixtures was developed using nanopore-enhanced opto-calorimetric spectroscopy. Opto-calorimetric spectroscopy based on specific molecular vibrational transitions in the mid infrared (IR) "molecular fingerprint" regime allows highly selective detection of VOCs vapor mixtures. Nanoporous anodic aluminum oxide (AAO) microcantilevers, fabricated using a two-step anodization and simple photolithography process, were utilized as highly sensitive thermomechanical sensors for opto-calorimetric signal transduction. The AAO microcantilevers were optimized by fine-tuning AAO nanopore diameter in order to enhance their thermomechanical sensitivity as well as their surface area. The thermomechanical sensitivity of a bilayer AAO microcantilever with a 60 nm pore diameter was approximately 1 μm/K, which is far superior to that of a bilayer plain silicon (Si) microcantilever. The adsorbed molecules of VOCs mixtures on the AAO microcantilever were fully recognized and quantified by variations of peak positions and amplitudes in the opto-calorimetric IR spectra as well as by shifts in the resonance frequency of the AAO microcantilever with the adsorbed molecules. Furthermore, identification of complex organic compounds with a real industrial sample was demonstrated by this e-nose system.

Quantum dynamics of CO-H₂ in full dimensionality.

Accurate rate coefficients for molecular vibrational transitions due to collisions with H₂, critical for interpreting infrared astronomical observations, are lacking for most molecules. Quantum calculations are the primary source of such data, but reliable values that consider all internal degrees of freedom of the collision complex have only been reported for H₂-H₂ due to the difficulty of the computations. Here we present essentially exact, full-dimensional dynamics computations for rovibrational quenching of CO due to H₂ impact. Using a high-level six-dimensional potential surface, time-independent scattering calculations, within a full angular momentum coupling formulation, were performed for the de-excitation of vibrationally excited CO. Agreement with experimentally determined results confirms the accuracy of the potential and scattering computations, representing the largest of such calculations performed to date. This investigation advances computational quantum dynamical studies representing initial steps towards obtaining CO-H₂ rovibrational quenching data needed for astrophysical modelling.

Mid-Infrared Resonant Ablation of PMMA

Laser ablation proved to be a reliable micro-fabrication technique for patterning and structuring of both thin film and bulk polymer materials. In most of the industrial applications ultra-violet (UV) laser sources are employed, however they have limitations such as maintenance costs and practical issues. As an alternative and promising approach, mid-infrared resonant laser ablation (RIA) has been introduced, in which the laser wavelength is tuned to one of the molecular vibrational transi-tions of the polymer to be ablated. Consequently, the technique is selective in respect of processing a diversity of polymers which usually have different infrared absorption bands. In this paper, we present mid-infrared resonant ablation of PolyMethyl MethAcrylate (PMMA), employing nanosec-ond laser pulses tunable between 3 and 4 microns. This RIA nanosecond laser set-up is based on a commercial laser at 1064 nm pumping a singly resonant Optical Parametric Oscillator (OPO) built around a Periodically-Poled Lithium Niobate (PPLN) crystal with several Quasi-Phase Matching (QPM) periods. RIA has been successfully demonstrated for structuring bulk PMMA, and selective patterning of PMMA thin films on a glass substrate has been implemented.

Characterizing of variation in the proton-to-electron mass ratio via precise measurements of molecular vibrational transition frequencies

We propose measurements of v,N=0,0→(1,0) transition frequencies of alkali earth–alkali diatomic molecules and alkali earth-hydride molecular ions. We show that the vibrational transitions considered here are useful for detecting a possible variation in the proton–electron mass ratio, possibly at the 10−16 sensitivity level. In the experiments, cold alkali earth–alkali molecules, obtained by binding cold atoms or by molecular laser cooling, are trapped by laser light at a frequency, at which the Stark shift is eliminated. Alkali earth-hydride molecular ions are sympathetically cooled with another ion to form a string crystal at the position, at which the electric field is zero. The vibrational transitions are observed by the Raman transition induced by two lasers with frequencies, at which the Stark shift is eliminated.

FT-IR, FT-Raman and DFT quantum chemical study on the molecular conformation, vibrational and electronic transitions of 1-(m-(trifluoromethyl)phenyl)piperazine

The FTIR and FT-Raman spectra of 1-(m-(trifluoromethyl)phenyl)piperazine [TFMPP] have been recorded in the region 4000–400cm−1 and 3500–100cm−1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6–311++G(d,p) basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. A detailed interpretation of the infrared and Raman spectra were also reported based on potential energy distribution (PED). UV–Vis spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. Furthermore, molecular electrostatic potential is performed and also the calculated HOMO and LUMO energies show that charge transfer occurs within the molecule.

FT-Raman, FT-IR, UV spectroscopic, NBO and DFT quantum chemical study on the molecular structure, vibrational and electronic transitions of clopidogrel hydrogen sulfate form 1: A comparison to form 2

Clopidogrel hydrogen sulfate (+)-(S)-(2-chlorophenyl)-6,7-dihydrothieno[3,2-c]pyridine-5(4H)-acetate sulfate (1:1), is a selective adenosine diphosphate (ADP) receptor antagonist often used in the treatment of coronary artery, peripheral vascular and cerebrovascular diseases. In the present communication, a comparative study of two polymorphic forms (forms 1 and 2) of clopidogrel hydrogen sulfate (CLP) has been reported. There is difference in conformation and intermolecular hydrogen bonding pattern of two forms. These differences are nicely reflected in the vibrational spectra. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands of CLP form 1 are interpreted with the aid of structure optimizations and normal mode analysis based on ab initio HF and DFT method employing 6-311++G(d,p) basis. Polymorphism in CLP have been studied using various characterization tools like FT-Raman, FT-IR spectroscopy and DSC in combination with the quantum chemical calculations. UV–vis spectroscopic studies along with HOMO–LUMO analysis of both polymorphs were performed. The solvent effect calculated by TD-DFT/IEF-PCM/6-31G model results complements with the experimental findings. Stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis.