Exotic Molecules Research Articles

In situ observation of chemistry in Rydberg molecules within a Bose-Einstein-condensate

We often infer the state of systems in nature indirectly, for example, in high-energy physics by the interaction of particles with an ambient medium. We adapt this principle to energies 9 orders of magnitude smaller, to classify the final state of exotic molecules after internal conversion of their electronic state, through their interaction with an ambient quantum fluid, a Bose-Einstein condensate (BEC). The BEC is the ground state of a million bosonic atoms near zero temperature, and a single embedded ultra-long-range Rydberg molecule can coherently excite waves in this fluid, which carry telltale signatures of its dynamics. Bond lengths exceeding a micrometer allow us to observe the molecular fingerprint on the BEC , via optical microscopy. Interpreting images in comparison with simulations strongly suggests that the molecular electronic state rapidly converts from the initially excited S and D orbitals to a much more complex molecular state (called “trilobite”), marked by a maximally localized electron. This internal conversion liberates energy, such that one expects final-state particles to move rapidly through the medium, which is however ruled out by comparing experiment and simulations. The molecule thus must strongly decelerate in the medium, for which we propose a plausible mechanism. Our experiment demonstrates a medium that facilitates and records an electronic state change of embedded exotic molecules in ultracold chemistry, with sufficient sensitivity to constrain velocities of final-state particles. Published by the American Physical Society 2024

Predicting the rotational dependence of line broadening using machine learning

Correct pressure broadening is essential for modelling radiative transfer in atmospheres, however data are lacking for the many exotic molecules expected in exoplanetary atmospheres. Here we explore modern machine learning methods to mass produce pressure broadening parameters for a large number of molecules in the ExoMol data base. To this end, state-of-the-art machine learning models are used to fit to existing, empirical air-broadening data from the HITRAN database. A computationally cheap method for large-scale production of pressure broadening parameters is developed, which is shown to be reasonably (69%) accurate for unseen active molecules. This method has been used to augment the previously insufficient ExoMol line broadening diet, providing air-broadening data for all ExoMol molecules, so that the ExoMol database has a full and more accurate treatment of line broadening. Suggestions are made for improved air-broadening parameters for species present in atmospheric databases.

Stretchable, Strong, Recyclable Helicide Elastomer Based on Dynamic Covalent Interactions.

Current methods for making and disposing synthetic polymers have been widely pursued and are largely unsustainable. As a part of the solution, the reversible nature of dynamic covalent bonds emerges as an extraordinarily diverse and valuable feature in the development of exotic molecules and extended structures. With these bonds, it should be possible to construct recyclable and mechanically interlocked molecular structures using relatively simple precursors with preorganized geometries. A new helicide-based elastomer network is developed here with self-healing, recycling, and degradation features using a similar concept. The best self-healing performance (100%) was noted over 10-20 min, with various H2O, HCl, and NaOH solutions that delivered mechanical properties in the 1-1.4 MPa range. For hydrolytic degradation, the parameters are defined based on the type of binding, the pH of the solutions, and the copolymer network, which endowed a degradation time of approximately 4-11 h for each prepared sample. However, due to the reversible nature of the dynamic bonds, the material showed good recyclable mechanical properties compared to the pristine samples after five consecutive cycles, which meet the requirements of recyclable materials and recyclable packaging.

From the laboratory to the interstellar medium: a strategy to search for exotic molecules in space

The chemistry of the interstellar medium occurs under extreme conditions and can lead to the formation of exotic molecules. These are species that on Earth are unstable and/or highly reactive. Their discovery in space is usually based on the astronomical observation of their rotational fingerprints, which requires an accurate laboratory investigation. This is based on a strategy that starts from the interplay of experiment and theory. State-of-the-art quantum-chemical calculations are used to predict the relevant spectroscopic information required to guide the spectral recording, analysis and assignment. Rotational spectra measurements are then performed in the centimeter-/millimeter-/submillimeter-wave region, thereby exploiting efficient on-the-fly production protocols for exotic molecules. Subsequently, the spectral analysis leads to accurate spectroscopic parameters, which are then used for setting up accurate line catalogs for astronomical searches and detections. This review is based on the strategy developed and the results obtained at the ROT&Comp Lab of the University of Bologna.

Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes.

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e., anthracene, pyrene, and perylene, which are intrinsically capable of supporting energy transfer and exciplex formation. The possible coconformations of the homo[2]catenanes, on account of their dynamic behavior, have been probed by Density Functional Theory calculations. The unique photophysical properties of these exotic molecules have been explored by steady-state and time-resolved absorption and fluorescence spectroscopies. The tetracationic pyrene-perylene cyclophane system exhibits emission emanating from a highly efficient Förster resonance energy transfer (FRET) mechanism which occurs in 48 ps, while the octacationic homo[2]catenane displays a weak exciplex photoluminescence following extremely fast (<0.3 ps) exciplex formation. The in-depth fundamental understanding of these photophysical processes involved in the fluorescence of bischromophoric cyclophanes and homo[2]catenanes paves the way for their use in future bioapplications and photonic devices.

Forming molecular states with hadronic rescattering

A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the chi _{c1}(3872) resonance, a possible tetraquark state, as well as three possible pentaquark states, P_c^+(4312), P_c^+(4440), and P_c^+(4457). For the P_c^+ states, the expected cross section from Lambda _b decays is compared to the hadronic-rescattering production. The chi _{c1}(3872) cross section is compared to the fiducial chi _{c1}(3872) cross-section measurement by LHCb and found to contribute at a level of {mathcal {O}({1%})}. Finally, the expected yields of mathrm {P_c^{+}} production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt mathrm {P_c^{+}} signal from hadronic rescattering.

Stabilizing the Exotic Carbonic Acid by Bisulfate Ion.

Carbonic acid is an important species in a variety of fields and has long been regarded to be non-existing in isolated state, as it is thermodynamically favorable to decompose into water and carbon dioxide. In this work, we systematically studied a novel ionic complex [H2CO3·HSO4]− using density functional theory calculations, molecular dynamics simulations, and topological analysis to investigate if the exotic H2CO3 molecule could be stabilized by bisulfate ion, which is a ubiquitous ion in various environments. We found that bisulfate ion could efficiently stabilize all the three conformers of H2CO3 and reduce the energy differences of isomers with H2CO3 in three different conformations compared to the isolated H2CO3 molecule. Calculated isomerization pathways and ab initio molecular dynamics simulations suggest that all the optimized isomers of the complex have good thermal stability and could exist at finite temperatures. We also explored the hydrogen bonding properties in this interesting complex and simulated their harmonic infrared spectra to aid future infrared spectroscopic experiments. This work could be potentially important to understand the fate of carbonic acid in certain complex environments, such as in environments where both sulfuric acid (or rather bisulfate ion) and carbonic acid (or rather carbonic dioxide and water) exist.

Custom Molecular Design of Ligands for Perovskite Photovoltaics

ConspectusPerovskite photovoltaics have witnessed overwhelming success owing to their high power conversion efficiency, low voltage deficit, sensitive photoelectric response and good operational stability. However, solution-processed, polycrystalline perovskite films inevitably contain a high density of crystallographic defects, such as uncoordinated ions and dangling bonds at the surfaces and grain boundaries, which can result in charge recombination, thus causing energy loss and impaired device performance. These intrinsic imperfections can be remedied through a chemically induced intermarriage between halide perovskites of soft crystallographic nature and judiciously designed exotic ligand molecules. Utilizing rational molecular design of the component moieties, i.e., the core and tail functional groups, the ligand molecules can be endowed with both more comprehensive and salient advantages to further boost device performance, thus setting perovskite photovoltaics on course for a more prosperous future.In this Account, we present our narrative of designing a series of favorable ligand molecules with multifunctionalities in terms of crystal growth modulation, grains cross-linking, defect passivation, surface functionalization, phase stabilization, and moisture invasion inhibition of perovskite films and summarize the advances made in designing molecular level custom ligands that have progressively lifted the record performances of perovskite photovoltaics. We first identify the origins of imperfections in perovskites and their detrimental impacts on device efficiency and stability. We then review feasible rules for ligand design, including tuning the length of the linear or branched alkyl chain core, the substitution of one or more carbon atoms with O, P, S, or NH, and the number of functional groups (double, triple, quadruple, or even multiple ones), to design “all-in-one” ligands with ideal molecular structures and multifunctionalities. The chemical interactions between ligands and perovskites (e.g., coordination bond, ionic bond, hydrogen bond, electrostatic interaction and chelation, etc.) are discussed, aiming to elucidate their impact on the necessary trade-off between defect passivation efficacy and charge transport property in ligand-modified perovskite films, and establish a triangular structure–property–performance relationship for perovskite-based optoelectronic devices with ligands modulation and passivation. We also insightfully explore novel ligand management strategies in perovskite quantum dots, especially the development of ligand-assisted cation exchange and surface ligand density optimization. Finally, we present an astute perspective of future trends in the rational design of innovative ligand molecules with desired structures and properties for more efficient, stable, perovskite-based optoelectronic devices.

Aromatics and Cyclic Molecules in Molecular Clouds: A New Dimension of Interstellar Organic Chemistry.

Astrochemistry lies at the nexus of astronomy, chemistry, and molecular physics. On the basis of precise laboratory data, a rich collection of more than 200 familiar and exotic molecules have been identified in the interstellar medium, the vast majority by their unique rotational fingerprint. Despite this large body of work, there is scant evidence in the radio band for the basic building blocks of chemistry on earth-five- and six-membered rings-despite long-standing and sustained efforts during the past 50 years. In contrast, a peculiar structural motif, highly unsaturated carbon in a chainlike arrangement, is instead quite common in space. The recent astronomical detection of cyanobenzene, the simplest aromatic nitrile, in the dark molecular cloud TMC-1, and soon afterward in additional prestellar and possibly protostellar sources, establishes that aromatic chemistry is likely widespread in the earliest stages of star formation. The subsequent discovery of cyanocyclopentadienes and even cyanonaphthalenes in TMC-1 provides further evidence that organic molecules of considerable complexity are readily synthesized in regions with high visual extinction but where the low temperature and pressure are remarkably low. This review focuses on laboratory efforts now underway to understand the rich transition region between linear and planar carbon structures using microwave spectroscopy. We present key features, advantages, and disadvantages of current detection methods, a discussion of the types of molecules found in space and in the laboratory, and approaches under development to identify entirely new species in complex mixtures. Studies focusing on the cyanation of hydrocarbons and the formation of benzene from acyclic precursors are highlighted, as is the role that isotopic studies might play in elucidating the chemical pathways to ring formation.

My Trajectory in Molecular Reaction Dynamics and Spectroscopy.

This is the story of a career in theoretical chemistry during a time of dramatic changes in the field due to phenomenal growth in the availability of computational power. It is likewise the story of the highly gifted graduate students and postdoctoral fellows that I was fortunate to mentor throughout my career. It includes reminiscences of the great mentors that I had and of the exciting collaborations with both experimentalists and theorists on which I built much of my research. This is an account of the developments of exciting scientific disciplines in which I was involved: vibrational spectroscopy, molecular reaction mechanisms and dynamics, e.g., in atmospheric chemistry, and the prediction of new, exotic molecules, in particular noble gas molecules. From my very first project to my current work, my career in science has brought me the excitement and fascination of research. What a wonderful pursuit!

Dressed Ion-Pair States of an Ultralong-Range Rydberg Molecule

We predict the existence of a universal class of ultralong-range Rydberg molecular states whose vibrational spectra form trimmed Rydberg series. A dressed ion-pair model captures the physical origin of these exotic molecules, accurately predicts their properties, and reveals features of ultralong-range Rydberg molecules and heavy Rydberg states with a surprisingly small Rydberg constant. The latter is determined by the small effective charge of the dressed anion, which outweighs the contribution of the molecule's large reduced mass. This renders these molecules the only known few-body systems to have a Rydberg constant smaller than R_{∞}/2.

Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Exotic Molecules and Radicals.

Aiming at completing the sets of FCI-quality transition energies that we recently developed (J. Chem. Theory Comput. 2018, 14, 4360-4379, ibid. 2019, 15, 1939-1956, and ibid. 2020, 16, 1711-1741), we provide, in the present contribution, ultra-accurate vertical excitation energies for a series of "exotic" closed-shell molecules containing F, Cl, P, and Si atoms and small radicals, such as CON and its variants, that were not considered to date in such investigations. This represents a total of 81 high-quality transitions obtained with a series of diffuse-containing basis sets of various sizes. For the exotic compounds, these transitions are used to perform benchmarks with a vast array of lower level models, i.e., CIS(D), EOM-MP2, (SOS/SCS)-CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, (SOS-)ADC(2), and ADC(3). Additional comparisons are made with literature data. For the open-shell compounds, we compared the performance of both the unrestricted and the restricted open-shell CCSD and CC3 formalisms.

On Possible Formation of Matter-Antimatter Exotic Molecular Structures

Possible formation of exotic matter-antimatter molecular structure is considered as one of the most challenging problems at International Laboratories of Particle Physics. In the present work, elaborate computer codes built for investigating four-body systems are employed for calculating the binding energies of exotic molecules composed of electrons, protons, muons, pions and their antiparticles. The results confirm the stability of these molecules against dissociation to their lowest possible channels. Based on these results, it is argued that possible creation of two universes immediately after the Big Bang should be considered. Particularly, it is proposed that an overlapping area might exist between the universe and antiuniverse in which continuous creation and annihilation of simple and complicated particle-antiparticle structures might occur. Antiparticles escaping from this area are considered as the origin of the minimal traces of antiparticles appearing in our universe. Recent interpretations of cosmic-rays and gamma-radiations observed at the edge of our universe could be thought of as evidences for supporting this argument. Furthermore, it is argued that possible formation of matter-antimatter molecular structures could open the gate in front of a new field of chemistry to be referred to as Antimatter Chemistry.

Sisyphus optical lattice decelerator

We experimentally demonstrate a variation on a Sisyphus cooling technique that was proposed for cooling antihydrogen. In our implementation, atoms are selectively excited to an electronic state whose energy is spatially modulated by an optical lattice, and the ensuing spontaneous decay completes one Sisyphus cooling cycle. We characterize the cooling efficiency of this technique on a continuous beam of Sr, and compare it with radiation pressure based laser cooling. We demonstrate that this technique provides similar atom number for lower end temperatures, provides additional cooling per scattering event and is compatible with other laser cooling methods. This method can be instrumental in bringing new exotic species and molecules to the ultracold regime.

Matter-Antimatter Physics at Low Energy

The main objective of the present paper is to discuss the consequences of matter-antimatter interaction at low energy. The production of large number of cooled antimatter in laboratory and the formation of exotic atoms composed of particles and antiparticles are reviewed. Particularly, the quantum mechanical treatment of Four-Body exotic molecules is shortly discussed. The main goal of the paper is to shed light on possible novel discoveries and applications based on the coexistence of matter and antimatter.

Quantum information-based analysis of electron-deficient bonds.

Recently, the correlation theory of the chemical bond was developed, which applies concepts of quantum information theory for the characterization of chemical bonds, based on the multiorbital correlations within the molecule. Here, for the first time, we extend the use of this mathematical toolbox for the description of electron-deficient bonds. We start by verifying the theory on the textbook example of a molecule with three-center two-electron bonds, namely, diborane(6). We then show that the correlation theory of the chemical bond is able to properly describe the bonding situation in more exotic molecules which have been synthesized and characterized only recently, in particular, the diborane molecule with four hydrogen atoms [diborane(4)] and a neutral zerovalent s-block beryllium complex, whose surprising stability was attributed to a strong three-center two-electron π bond stretching across the C-Be-C core. Our approach is of high importance especially in the light of a constant chase after novel compounds with extraordinary properties where the bonding is expected to be unusual.

Tying up topological chirality

Linked molecules have long captured chemists’ imaginations, and their synthesis even won researchers the 2016 Nobel Prize in Chemistry. But while these molecules are often discussed in terms of molecular motors and switches, Steve Goldup’s lab at the University of Southampton is more interested in understanding how to make them. Now, his team has developed a method for synthesizing and separating topologically chiral catenanes, enabling investigations of the exotic molecules’ properties (Chem 2019, DOI: 10.1016/j.chempr.2019.03.008). “The work is a major step forward,” says Nicholas Evans of Lancaster University. He says it’s the first demonstration of enantiopure samples of topologically chiral catenanes on a preparative scale. Topological chirality refers to a higher-level spatial orientation in these molecules. On their own, the catenane loops are not chiral. When they are interlinked, their chirality depends on their orientations relative to each other. The only way the chirality could be flipped would be to

Testosterone for depression?

There is an intrinsic appeal to the notion that testosterone might improve depressive symptoms in men. It is, after all, a natural substance — less need to worry that it is some exotic molecule cooked up by an anonymous medicinal chemist in some mega‐conglomerate corporate pharmaceutical lab — and we tend to associate it, at least in the popular imagination, with vigor, vitality, and, well, hardy manliness. And I haven't included in that list of imagined attributes its alluring mystique as a possible elixir of youth.

Exotic molecules consisting of an antiproton and a hydrogen atom

A theoretical study is conducted on the stability of exotic antiproton-hydrogen molecular anions ($\overline{p}\mathrm{H}$), which in the separated atom limit correlate with $\overline{p}+\mathrm{H}(n=2)$ ($n$ being the principal quantum number). The $\overline{p}\mathrm{H}$ molecule in the electronic ground state is highly unstable due to pair annihilation and autodetachment ($\ensuremath{\rightarrow}\overline{p}p+e$). However, if the $\overline{p}\mathrm{H}$ molecule is electronically excited, the molecular stability can be drastically improved. Since the excited states of the $\mathrm{H}$ atom have accidental degeneracy, the asymptotic form of the Born-Oppenheimer potential curve of $\overline{p}+\mathrm{H}(n=2)$ behaves as $1/{R}^{2}$ ($R$ being the relative distance), which can play a critical role in the bonding and stability of the molecule. It is found that the $\overline{p}\mathrm{H}$ molecule in the first electronic excited state and in a high rotational state is sufficiently stable and has a lifetime dominated by spontaneous radiative emission ($\ensuremath{\rightarrow}\overline{p}+\mathrm{H}+h\ensuremath{\nu}$). The $\overline{p}\mathrm{H}$ system is dynamically similar to ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$, which had been commonly considered to be unstable due to autodetachment. However, recent measurements of ion-beam sputtering unambiguously verified the existence of long-lived ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$ molecules in high rotational states. This suggests that the $\overline{p}\mathrm{H}$ molecules may actually be created if one employs experimental means such as the chemical sputtering of hydrogen-rich targets with $\overline{p}$ beams.

Photochemistry of OPN: Formation of Cyclic PON and Reversible Combination with Carbon Monoxide

Cyclic PON, a first 16-electron triatomic ring consisting of two first-row elements, has been generated through 193 nm laser photolysis of OPN in cryogenic matrices. When the photolysis (365 nm) was performed in the presence of CO, OPN combines CO and furnishes an exotic acyclic molecule OPNCO. Upon the 193 nm laser irradiation, OPNCO dissociates mainly to OPN and CO with traces of PN and CO2 . The identification of cyclic PON and OPNCO with IR spectroscopy is supported by 15 N-labeling experiments and quantum chemical calculations.