Cold Chemistry Research Articles

Chemistry in the GG Tau A Disk: Constraints from H2D+, N2H+, and DCO+ High Angular Resolution ALMA Observations

Resolved molecular line observations are essential for gaining insight into the physical and chemical structure of protoplanetary disks, particularly in cold, dense regions where planets form and acquire their chemical compositions. However, tracing these regions is challenging because most molecules freeze onto grain surfaces and are not observable in the gas phase. We investigated cold molecular chemistry in the triple stellar T Tauri disk GG Tau A, which harbours a massive gas and dust ring and an outer disk, using Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations. We present high angular resolution maps of N2H+ and DCO+ emission, with upper limits reported for H2D+, 13CS, and SO2. The radial intensity profile of N2H+ shows most emission near the ring’s outer edge, while DCO+ exhibits a double peak, one near the ring’s inner edge and the other in the outer disk. With complementary observations of lower-lying transitions, we constrained the molecular surface densities and rotation temperatures. We compared the derived quantities with model predictions across different cosmic-ray ionization (CRI) rates, carbon-to-oxygen (C/O) ratios, and stellar UV fluxes. Cold molecular chemistry, affecting the N2H+, DCO+, and H2D+ abundances, is most sensitive to the CRI rate, while the stellar UV fluxes and C/O ratios have minimal impact on these three ions. Our best model requires a low CRI rate of 10−18 s−1. However, it fails to match the low temperatures derived from N2H+ and DCO+, 12–16 K, which are much lower than the CO freezing temperature.

Theoretical Investigation of Rate Coefficients and Dynamical Mechanisms for N + N + N Three-Body Recombination Based on Full-Dimensional Potential Energy Surfaces

Three-body recombination reactions, in which two particles form a bound state while a third one bounces off after the collision, play significant roles in many fields, such as cold and ultracold chemistry, astrochemistry, atmospheric physics, and plasma physics. In this work, the dynamics of the recombination reaction for the N3 system over a wide temperature range (5000–20,000 K) are investigated in detail using the quasi-classical trajectory (QCT) method based on recently developed full-dimensional potential energy surfaces. The recombination products are N2(X) + N(4S) in the 14A″ state, N2(A) + N(4S) in the 24A″ state, and N2(X) + N(2D) in both the 12A″ and 22A″ states. A three-body collision recombination model involving two sets of relative translational energies and collision parameters and a time-delay parameter is adopted in the QCT calculations. The recombination process occurs after forming an intermediate with a certain lifetime, which has a great influence on the recombination probability. Recombination processes occurring through a one-step three-body collision mechanism and two distinct two-step binary collision mechanisms are found in each state. And the two-step exchange mechanism is more dominant than the two-step transfer mechanism at higher temperatures. N2(X) formed in all three related states is always the major recombination product in the temperature range from 5000 K to 20,000 K, with the relative abundance of N2(A) increasing as temperature decreases. After hyperthermal collisions, the formed N2(X/A) molecules are distributed in highly excited rotational and vibrational states, with internal energies mainly distributed near the dissociation threshold. Additionally, the rate coefficients for this three-body recombination reaction in each state are determined and exhibit a negative correlation with temperature. The dynamic insights presented in this work might be very useful to further simulate non-equilibrium dynamic processes in plasma physics involving N3 systems.

The effect of variations in cold plasma conditions on the detoxification of Aflatoxin M1 and degradation products

The aim of this study was to explore the chemical reactive species of different operating gases, and their effect on the degradation of aflatoxin M1 (AFM1) by cold plasma by measuring the reactive species concentration. Helium, at 80, 90 or 95%, was used mixed with oxygen, nitrogen and air. The efficacy of cold plasma on aflatoxin M1 (AFM1) reduction was improved when decreasing the ratio of helium in the gas mixture. The ratio of the gas mixtures changed the cold plasma chemistry believed to be due to the differences in the concentrations of the reactive species. The degradation products of AFM1 after cold plasma treatment using a helium/air gas mixture and the degradation pathway were identified by LCMS. AFM1 was oxidised by reactive species in the cold plasma to produce degradant products with, theoretically, lower toxicity than AFM1.

Background-free imaging of cold atoms in optical traps

Optical traps, including those used in atomic physics, cold chemistry, and quantum science, are widely used in the research on cold atoms and molecules. Owing to their microscopic structure and excellent operational capability, optical traps have been proposed for cold atom experiments involving complex physical systems, which generally induce violent background scattering. In this study, using a background-free imaging scheme in cavity quantum electrodynamics systems, a cold atomic ensemble was accurately prepared below a fiber cavity and loaded into an optical trap for transfer into the cavity. By satisfying the demanding requirements for the background-free imaging scheme in optical traps, cold atoms in an optical trap were detected with a high signal-to-noise ratio while maintaining atomic loading. The cold atoms were then transferred into the fiber cavity using an optical trap, and the vacuum Rabi splitting was measured, facilitating relevant research on cavity quantum electrodynamics. This method can be extended to related experiments involving cold atoms and molecules in complex physical systems using optical traps.

Effect of Cold Plasma Seed Treatment on Physiological and Biochemical Changes in Aged Mustard Seed Variety-RH0749

The low rate of seed germination is a major problem in modern agriculture. Cold-activated air plasma has been tested as a pre-treatment method to improve the rate and uniformity of the germination. In view of the widespread cultivation of mustard in India and other parts of the world, This study was conducted to determine alternative non-destructive seed treatment method based on cold plasma chemistry would offer a more viable alternative over traditional seed coating technologies Seed physiological characteristics as was modified in aged low vigour mustard seeds by coating the surface of the seeds with cold plasma process using a rotating plasma reactor during 2023-24 at CCS HAU, College of Agriculture Bawal. The source of atmospheric oxygen gas, nitrogen and heliun gas entering the plasma chamber during the reaction process determined the type of coating. Among the different treatments imposed, seed treatment with 300V at 10 Min significantly enhanced seed quality attributes viz., germination ( 92 %), root length ( 4.37 cm), shoot length ( 6.98 cm), mean seedling length (11.0 cm ), Seedling dry weight (2.67 mg) and SVI-I (1115), SVI-II (254), TDH (0.78 A480 nm) with lower electrical conductivity (14.20 dsm-1). The inhibitory effect noticed with a higher dose of plasma of 400v at 10 min suggested the need for judicious usage of these plasma frequencies in such applications. The first-ever report on the effect of new plasma state on seed germination and establishment of mustard revealed the positive influence that could be used as a seed treatment to enhance seed yield and quality.

Cold Chemistry is Different

Cold Chemistry is Different

A versatile apparatus for simultaneous trapping of multiple species of ultracold atoms and ions to enable studies of low energy collisions and cold chemistry.

We describe an apparatus where many species of ultracold atoms can be simultaneously trapped and overlapped with many species of ions in a Paul trap. Several design innovations are made to increase the versatility of the apparatus while keeping the size and cost reasonable. We demonstrate the operation of a three-dimensional (3D) magneto-optical trap (MOT) of 7Li using a single external cavity diode laser. The 7Li MOT is loaded from an atomic beam, with atoms slowed using a Zeeman slower designed to work simultaneously for Li and Sr. The operation of a 3D MOT of 133Cs, loaded from a 2D MOT, is demonstrated, and provisions for MOTs of Rb and K in the same vacuum manifold exist. We demonstrate the trapping of 7Li+ and 133Cs+ at different settings of the Paul trap and their detection using an integrated time-of-flight mass spectrometer. We present results on low energy neutral-neutral collisions (133Cs-133Cs, 7Li-7Li, and 133Cs-7Li collisions) and charge-neutral collisions (133Cs+-133Cs and 7Li+-7Li collisions). We show evidence of sympathetic cooling of 7Li+ (133Cs+) due to collisions with the ultracold 7Li (133Cs).

Cold Chemistry.

Cold Chemistry.

Electronic Structure, Spectroscopy, Cold Ion–Atom Elastic Collision Properties, and Photoassociation Formation Prediction of the (MgCs)+ Molecular Ion

In this paper, we extensively study the electronic structure, interactions, and dynamics of the (MgCs)+ molecular ion. The exchanges between the alkaline atom and the low-energy cationic alkaline earths, which are important in the field of cold and ultracold quantum chemistry, are studied. We use an ab initio approach based on the formalism of non-empirical pseudo-potential for Mg2+ and Cs+ cores, large Gaussian basis sets, and full-valence configuration interaction. In this context, the (MgCs)+ cation is treated as an effective two-electron system. Adiabatic potential energy curves and their spectroscopic constants for the ground and the first 20 excited states of 1,3Σ+ symmetries are determined. Furthermore, we identify the avoided crossings between the electronic states of 1,3Σ+ symmetries. These crossings are related to the charge transfer process between the two ionic limits, Mg/Cs+ and Mg+/Cs. Therefore, vibrational-level spacings and the transition and permanent dipole moments are presented and analyzed. Using the produced potential energy data, the ground-state scattering wave functions and elastic cross-sections are calculated for a wide range of energies. In addition, we predict the formation of a translationally and rotationally cold molecular ion (MgCs)+ in the ground-state electronic potential energy through a stimulated Raman-type process aided by ion–atom cold collision. In the low-energy limit (<1 mK), elastic scattering cross-sections exhibit Wigner law threshold behavior, while in the high-energy limit, the cross-sections act as a function of energy E go as E−1/3. A qualitative discussion about the possibilities of forming cold (MgCs)+ molecular ions by photoassociative spectroscopy is presented.

First detection of deuterated methylidyne (CD) in the interstellar medium

While the abundance of elemental deuterium is relatively low (D/H ~ a few ×10−5), orders of magnitude higher D/H abundance ratios have been found for many interstellar molecules, enhanced by deuterium fractionation. In cold molecular clouds (T < 20 K), deuterium fractionation is driven by the H2D+ ion, whereas at higher temperatures (T ≥ 20–30 K) gas-phase deuteration is controlled by reactions with CH2D+ and C2HD+. While the role of H2D+ in driving cold interstellar deuterium chemistry is well understood, thanks to observational constraints from direct measurements of H2D+, deuteration stemming from CH2D+ is far less understood as a result of the absence of direct observational constraints of its key ions. Therefore, making use of chemical surrogates is imperative in order to explore deuterium chemistry at intermediate temperatures. Formed at an early stage of ion-molecule chemistry directly from the dissociative recombination of CH3+ (CH2D+), CH (CD) is an ideal tracer for investigating deuterium substitution initiated by reactions with CH2D+. This paper reports the first detection of CD in the interstellar medium (ISM), carried out using the APEX 12 m telescope toward the widely studied low-mass protostellar system IRAS 16293–2422. Observed in absorption towards the envelope of the central protostar, the D/H ratio derived from the column densities of CD and CH is found to be 0.016 ± 0.003. This is an order of magnitude lower than the values found for other small molecules like C2H and H2CO observed in emission but whose formation, which is similar to that of CH, is also initiated via pathways involving warm deuterium chemistry. Gas-phase chemical models reproducing the CD/CH abundance ratio suggest that it reflects ‘warm deuterium chemistry’ (which ensues in moderately warm conditions of the ISM) and illustrates the potential use of the CD/CH ratio in constraining the gas temperatures of the envelope gas clouds it probes.

Superfluid Helium Drops Levitated in High Vacuum.

We demonstrate the trapping of millimeter-scale superfluid helium drops in high vacuum. The drops are sufficiently isolated that they remain trapped indefinitely, cool by evaporation to 330mK, and exhibit mechanical damping that is limited by internal processes. The drops are also shown to host optical whispering gallery modes. The approach described here combines the advantages of multiple techniques, and should offer access to new experimental regimes of cold chemistry, superfluid physics, and optomechanics.

Integration of structural, hydrogeological and thermal remote sensing data for the determination of geothermal capacity A case study of the Edremit (Balıkesir) Basin

Basins formed on active strike-slip faults are important prospect areas for geothermal energy exploration since the crust gets thinner in these areas and tectonic structures provide favorable conditions for heat-fluid circulation and transport. The Edremit (Balıkesir) Basin holds a great promise for the discovery of new geothermal energy sources. The objective of the recent study is to evaluate the geothermal capacity of the Edremit Basin utilizing tectonic, geological, and hydrogeological studies, combining remote sensing (land surface temperature-LST, hydrothermal alteration, and multi-temporal InSAR (MT-InSAR) assessments). We present structural literature data and the results of field mapping, which revealed the geometry, kinematics, and dynamics of structural features, geological units as geothermal system components, thermal and cold water chemistry, and thermal infrared remote sensing analysis. For the purpose of assessing new targets and recent geothermal capacity, these data are combined and evaluated. According to the outcomes of the study, the fault pattern in the Edremit Basin is generated by N-S extension, which produced E-W dominant striking normal faults with a heritage of paleostructures oriented in various directions. According to remote sensing analyses, the primary LST regions in the basin are defined by the active faults. Therefore, a high sodium sulfate ratio recorded in the chemical analyses of the water samples indicates a deep circulation and high possibility for the presence of thermal water. Consequently, our findings are consistent with the work to include thorough field geology surveys, structural patterns, LST, and water chemistry to refined exploration process.

An SMA Survey of Chemistry in Disks Around Herbig AeBe Stars

Protoplanetary disks around Herbig AeBe stars are exciting targets for studying the chemical environments where giant planets form. Save for a few disks, however, much of Herbig AeBe disk chemistry is an open frontier. We present a Submillimeter Array ∼213–268 GHz pilot survey of millimeter continuum CO isotopologs and other small molecules in disks around five Herbig AeBe stars (HD 34282, HD 36112, HD 38120, HD 142666, and HD 144432). We detect or tentatively detect 12CO 2–1 and 13CO 2–1 from four disks, C18O 2–1 and HCO+ 3–2 from three disks, HCN 3–2, CS 5–4, and DCO+ 3–2 from two disks, and C2H 3–2 and DCN 3–2 from one disk each. H2CO 3–2 is undetected at the sensitivity of our observations. The millimeter continuum images of HD 34282 suggest a faint, unresolved source ∼5.″0 away, which could arise from a distant orbital companion or an extended spiral arm. We fold our sample into a compilation of T Tauri and Herbig AeBe/F disks from the literature. Altogether, most line fluxes generally increase with millimeter continuum flux. Line flux ratios between CO 2–1 isotopologs are nearest to unity for the Herbig AeBe/F disks. This may indicate emitting layers with relatively similar, warmer temperatures and more abundant CO relative to the disk dust mass. Lower HCO+ 3–2 flux ratios may reflect lower ionization in Herbig AeBe/F disks. Lower detection rates and flux ratios for DCO+ 3–2, DCN 3–2, and H2CO 3–2 suggest smaller regimes of cold chemistry around the luminous Herbig AeBe/F stars.

A single ion immersed in an ultracold gas: from cold chemistry to impurity physics

A single ion in an ultracold gas is a versatile experimental platform to study interactions between charged and neutral particles in a controllable manner. When the gas density is large enough, a single ion can be viewed as an impurity in a sea of ultracold atoms or molecules. On the other hand, that single ion can also undergo a chemical reaction with atoms or molecules in the gas. This article discusses the dynamics of a charged impurity in an ultracold bath and the interplay between cold chemistry and impurity physics.

Focus on the cold and ultracold chemistry of atoms, ions and molecules

Focus on the cold and ultracold chemistry of atoms, ions and molecules

The Formation of Monosubstituted Cyclopropenylidene Derivatives in the Interstellar Medium via Neutral–Neutral Reaction Pathways

Five substituted cyclopropenylidene derivatives (c-C3HX, X=CN, OH, F, NH2), all currently undetected in the interstellar medium (ISM), are found herein to have mechanistically viable, gas-phase formation pathways through neutral–neutral additions of ·X onto c-C3H2. The detection and predicted formation mechanism of c-C3HC2H introduces a need for the chemistry of c-C3H2 and any possible derivatives to be more fully explored. Chemically accurate CCSD(T)-F12/cc-pVTZ-F12 calculations provide exothermicities of additions of various radical species to c-C3H2, alongside energies of submerged intermediates that are crossed to result in product formation. Of the novel reaction mechanisms proposed, the addition of the cyano radical is the most exothermic at -16.10 kcal mol−1. All five products are found to or are expected to have at least one means of associating barrierlessly to form a submerged intermediate, a requirement for the cold chemistry of the ISM. The energetically allowed additions arise as a result of the strong electrophilicity of the radical species as well as the product stability gained through substituent-ring conjugation.

Controllable three-dimensional electrostatic lattices for manipulation of cold polar molecules

Engineering many-body systems of particles in lattices has attracted intense interest in the last few decades, thanks to their promising applications such as in quantum computation or topological matter. While lattices of different dimensions have been demonstrated with magnetic and/or optical fields, little work has been done upon three-dimensional (3D) electrostatic lattices to tame polar molecules. Here, we propose a 3D electrostatic lattice consisting of periodically distributed square-patterned electrodes in space, whose potentials reach tens of millikelvin and can be controlled easily. Detailed analysis and Monte Carlo simulations indicate that ${\mathrm{ND}}_{3}$ molecules in its $|J,KM\ensuremath{\rangle}=|1,\ensuremath{-}1\ensuremath{\rangle}$ state can be effectively trapped and evaporatively cooled. In addition, replacing the electrodes with different patterns enables realizing 3D electric lattices with new topological geometry (e.g., honeycomb or kagome). As a natural extension of the 3D optical and magnetic lattices, the 3D electrostatic lattice offers intriguing perspectives for cold chemistry, quantum simulation, and precision metrology.

The Reaction of the Methylidyne Radical (CH X2Π) with the Hydrogen Cyanide (HCN X1∑+) Molecule in Cold Molecular Clouds and Planetary Atmospheres

The reaction of the methylidyne (CH; X2Π) radical with hydrogen cyanide (HCN; X1∑) molecule was studied at a collision energy of 4.0 kJ/mol with ab initio calculations of the potential energy surface (PES). Geometries and potential energies of reactants, products, intermediates and transition states (TS) for the reaction were found by means of ab initio quantum chemical method ωB97xd/cc-pVTZ and the higher-level corrections were evaluated at the CCSD(T)-F12 level of theory with the cc-pVQZ-f12 (E1) and cc-pVTZ-f12 (E2) basis sets. The calculated values then were used for extrapolation to the complete basis set (CBS) limit using the two-point expression E(CBS) = E1 + 0.69377 × (E1 – E2). Analysis of the found energies, structural and kinetic characteristics of the involved compounds allowed us to determine the reaction paths leading to the formation of linear and cyclic intermediates, as well as to the formation of atomic and molecular hydrogen. Those results were utilized in Rice−Ramsperger−Kassel−Marcus calculations of the product branching ratios at the zero pressure limit – common approach in modelling of the cold molecular clouds chemistry. Mechanism identified emphasizes importance of the CH+HCN reaction as an important supplier of the initial bricks for building heterocyclic hydrocarbons in extreme environments.

Unlocking the sulphur chemistry in intermediate-mass protostars of Cygnus X

Context. The chemistry of sulphur-bearing species in the interstellar medium remains poorly understood, but might play a key role in the chemical evolution of star-forming regions. Aims. Coupling laboratory experiments to observations of sulphur-bearing species in different parts of star-forming regions, we aim to understand the chemical behavior of the sulphur species in cold and warm regions of protostars, and we ultimately hope to connect them. Methods. We performed laboratory experiments in which we tested the reactivity of hydrogen sulfide (H2S) on a cold substrate with hydrogen and/or carbon monoxide (CO) under different physical conditions that allowed us to determine the products from sulphur reactions using a quadrupole mass spectrometer. The laboratory experiments were complemented by observations. We observed two luminous binary sources in the Cygnus-X star-forming complex, Cygnus X-N30 and N12, covering a frequency range of 329–361 GHz at a spatial resolution of 1′′5 with the SubMillimeter Array (SMA). This study was complemented by a 3 mm line survey of Cygnus X-N12 covering specific frequency windows in the frequency ranges 72.0–79.8 GHz at a spatial resolution of 34′′0–30′′0 and 84.2–115.5 GHz at a spatial resolution of 29′′0–21′′0, with the IRAM-30 m single-dish telescope. Column densities and excitation temperatures were derived under the local thermodynamic equilibrium approximation. Results. We find that OCS is a direct product from H2S reacting with CO and H under cold temperatures (T < 100 K) from laboratory experiments. OCS is therefore found to be an important solid-state S-reservoir. We identify several S-species in the cold envelope of Cyg X-N12, principally organo-sulphurs (H2CS, CS, OCS, CCS, C3S, CH3SH, and HSCN). For the hot cores of Cyg X-N12 and N30, only OCS, CS and H2CS were detected. We found a difference in the S-diversity between the hot core and the cold envelope of N12, which is likely due to the sensitivity of the observations toward the hot core of N12. Moreover, based on the hot core analysis of N30, the difference in S-diversity is likely driven by chemical processes rather than the low sensitivity of the observations. Furthermore, we found that the column density ratio of NCS/NSO is also an indicator of the warm (NCS/NSO > 1), cold (NCS/NSO < 1) chemistries within the same source. The line survey and molecular abundances inferred for the sulphur species are similar for protostars N30 and N12 and depends on the protostellar component targeted (i.e., envelope or hot core) rather than on the source itself. However, the spatial distribution of emission toward Cyg X-N30 shows differences compared to N12: toward N12, all molecular emission peaks on the two continuum sources, whereas emission is spatially distributed and shows variations within molecular families (N, O, and C families) toward N30. Moreover, this spatial distribution of all the identified S-species is offset from the N30 continuum peaks. The sulphur-bearing molecules are therefore good tracers to connect the hot and cold chemistry and to provide insight into the type of object that is observed.

Efficient rotational cooling of a cold beam of barium monofluoride

The ability to cool and trap a large number of molecules is currently a crucial challenge for the implementation of various applications in fundamental physics and cold chemistry. We here present an optical cooling of the internal degrees of freedom which maximizes the number of molecules in a minimum number of rotational states. Our demonstration is achieved on a supersonic beam of barium monofluoride seeded in argon, a process that leads to a rotational temperature T rot ≈ 12 K. The rotation is then cooled by our optical pumping to approximately T rot ≈ 0.8 K which, compared to the initial rotational distribution, corresponds to an increase of the number of molecules in the lowest rotational state by one order of magnitude. Our method employs two light sources coming from tapered amplifiers. The first source, dedicated to the rotational cooling of molecules occupying the fundamental vibrational level, is optimized thanks to a spectral shaping whose resolution is comparable to the separation of the relevant rotational levels. The second source is used to pump the molecules back to the fundamental vibrational level when they escape from it. This work focuses on the relevant features of these two types of optical pumping.