Dissociation Of CS2 Research Articles

Mechanochemical activation of NHC–CS2 adducts for the generation of N‐heterocyclic carbenes

AbstractStable N‐heterocyclic carbenes (NHCs) have garnered significant attention in synthetic chemistry due to their versatile applications. In this study, we explored a novel mechanochemical method for the generation of free carbenes, which could be a good complement to traditional approaches that require strong bases or reductants. Ball milling of NHC–CS2 adducts at room temperature successfully resulted in the quantitative formation of free carbenes that can be subsequently trapped by sulfur or selenium. Importantly, heating NHC–CS2 adducts in solution phase did not lead to the successful generation of free carbenes, in agreement with the high activation energy required for NHC–CS2 dissociation. These findings underscore the potential of ball milling as a robust and versatile approach for generating NHCs from stable NHC‐small molecule adducts, and opens new avenues for developing mechanochemical strategies for generating valuable NHC‐derived compounds.

Ultrafast Extreme Ultraviolet Photoelectron Spectroscopy of Nonadiabatic Photodissociation of CS2 from 1B2 (1Σu+) State: Product Formation via an Intermediate Electronic State.

We studied nonadiabatic dissociation of CS2 from the 1B2 (1Σu+) state using ultrafast extreme ultraviolet photoelectron spectroscopy. A deep UV (200 nm) laser using the filamentation four-wave mixing method and an extreme UV (21.7 eV) laser using the high-order harmonic generation method were employed to achieve the pump-probe laser cross-correlation time of 48 fs. Spectra measured with a high signal-to-noise ratio revealed clear dynamical features of vibrational wave packet motion in the 1B2 state; its electronic decay to lower electronic state(s) within 630 fs; and dissociation into S(1D2), S(3PJ), and CS fragments within 300 fs. The results suggest that both singlet and triplet dissociation occur via intermediate electronic state(s) produced by electronic relaxation from the 1B2 (1Σu+) state.

In-Situ Photo-Dissociation and Polymerization of Carbon Disulfide with Vacuum Ultraviolet Microplasma Flat Lamp for Organic Thin Films

Vacuum UV (VUV) photo-dissociation for a liquid phase organic compound, carbon disulfide (CS2), has been investigated. 172 nm (7.2 eV) VUV photons from Xe2* excimers in a microcavity plasma lamp irradiated free-standing liquid droplets on Si substrate in each a nitrogen environment and an atmospheric air environment. Selective and rapid dissociation of CS2 into C-C, C-S or C-O-S based fragments was observed in the different gas environments during the reaction. Thin-layered polymeric microdeposites have been identified by characterization with a Scanning electron microscope (SEM), Energy dispersive x-ray spectroscopy (EDX), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This novel photo-process from the flat VUV microplasma lamp introduces another pathway of low-temperature organic (or synthetic) conversion for large area deposition. The in-situ, selective conversion of various organic precursors can be potentially used in optoelectronics and nanotechnology applications.

Time resolved detection of the S(1D) product of the UV induced dissociation of CS2.

The products formed following the photodissociation of UV (200 nm) excited CS2 are monitored in a time resolved photoelectron spectroscopy experiment using femtosecond XUV (21.5 eV) photons. By spectrally resolving the electrons, we identify separate photoelectron bands related to the CS2 + hν → S(1D) + CS and CS2 + hν → S(3P) + CS dissociation channels, which show different appearance and rise times. The measurements show that there is no delay in the appearance of the S(1D) product contrary to the results of Horio et al. [J. Chem. Phys. 147, 013932 (2017)]. Analysis of the photoelectron yield associated with the atomic products allows us to obtain a S(3P)/S(1D) branching ratio and the rate constants associated with dissociation and intersystem crossing rather than the effective lifetime observed through the measurement of excited state populations alone.

All in one plasma process: From the preparation of S-C composite cathode to alleviation of polysulfide shuttle in Li-S batteries

Tremendous efforts have been made to improve the electrochemical performance of the lithium-sulfur batteries. However, challenges remain in achieving fast electronic and ionic transport while accommodate the significant cathode volumetric change. On the other hand, the severe capacity decay mainly attributed to polysulfide shuttle also hampers the practical applications. Here, we report a simple, low-cost, and eco-friendly method for the one-step preparation of a binder-free S-C composite cathode by plasma dissociation of CS2 containing gases at room-temperature. The key issue of polysulfide shuttle effect in Li-S batteries is also effectively resolved just by the introduction of N2 into the precursor gases. The electrode exhibits a high reversible capacity of ~600 mAh/g of the total hybrid of S + C at 100 mA/g after 100 cycles with an excellent initial coulombic efficiency of nearly 100%. The cells also demonstrate along cycle life and an extremely high capacity of ~306 mAh/g even after 300 cycles at 1 A/g with a high coulombic efficiency of about 100%. The proposed method will open the way for the plasma applications in facile preparation of Li-S batteries and the improvement of its electrochemical performance.

Biological Thiols and Carbon Disulfide: The Formation and Decay of Trithiocarbonates under Physiologically Relevant Conditions.

Carbon disulfide is an environmental toxin, but there are suggestions in the literature that it may also have regulatory and/or therapeutic roles in mammalian physiology. Thiols or thiolates would be likely biological targets for an electrophile, such as CS2, and in this context, the present study examines the dynamics of CS2 reactions with various thiols (RSH) in physiologically relevant near-neutral aqueous media to form the respective trithiocarbonate anions (TTC–, also known as “thioxanthate anions”). The rates of TTC– formation are markedly pH-dependent, indicating that the reactive form of RSH is the conjugate base RS–. The rates of the reverse reaction, that is, decay of TTC– anions to release CS2, is pH-independent, with rates roughly antiparallel to the basicities of the RS– conjugate base. These observations indicate that the rate-limiting step of decay is simple CS2 dissociation from RS–, and according to microscopic reversibility, the transition state of TTC– formation would be simple addition of the RS– nucleophile to the CS2 electrophile. At pH 7.4 and 37 °C, cysteine and glutathione react with CS2 at a similar rate but the trithiocarbonate product undergoes a slow cyclization to give 2-thiothiazolidine-4-carboxylic acid. The potential biological relevance of these observations is briefly discussed.

Carbon disulfide (CS2) adsorption and dissociation on the Cu(100) surface: A quantum chemical study

Density functional theory (DFT) is used to examine the adsorption and dissociation of CS2 on the Cu(100) surface. This study evaluates the adsorption energies and geometries of the species (CS2, CS, C and S) adsorption on the Cu(100) surface, as well as that coadsorption of CS and a S atom, and that coadsorption of C atom and two S atoms. The results indicate that the species (CS2, CS, C and S) are strongly chemadsorbed on the Cu(100) surface through the CCu and/or SCu bond with an increased adsorption energy (C/S/S>S/CS>CS2). Two pathways for CS2 dissociation on the Cu(100) surface are constructed, and the energy barrier and reaction energy of each step are calculated. It shows that the dissociated energy barrier of the second CS bond is 0.25eV higher than that of the first CS bond in the pathway 1, but in the pathway 2, the dissociated energy barrier of the second CS bond is 0.11eV lower than that of the first CS bond. Comparing the highest dissociated energy barrier of pathway 1 (0.68eV) and pathway 2 (0.5eV), the structure of S/C/S(II) is regarded as a preferable product for the dissociation of CS2 on the Cu(100) surface.

Theoretical determination of the microstructure of Cs covering of Mo in negative ion sources for nuclear fusion applications

Cs is the most well known catalyst used in negative ion sources for fast neutral beam generation employed in nuclear fusion, where the element is evaporated and deposited on Mo surfaces forming non permanent films. In this paper the interaction of Cs with Mo under conditions of interest for negative ion sources is studied using different methods. Cs–Mo potential has been characterized starting from high level electronic calculations for two atoms. Mo–Mo and Mo–Cs potentials are based on new fits of the literature data. Density functional theory calculations on a reduced cell are used to determine the adsorption energy of Cs on Mo for different sites. Good reproduction of experimental results, when available, is achieved (e.g. Mo crystal data, Cs2 dissociation energy) and new results for the evaporation energy of Cs from Mo surfaces, CsMo dissociation energy, adatom geometry etc. are reported and tabulated. A functional expression of the Cs–Mo[0 0 1] interaction potential is proposed based on these ab-initio results. The use of this potential is illustrated by classical MD calculations for the morphology for Cs partial layers on Mo[0 0 1]. Calculations show that the interaction between Cs and the surface leads to peculiar morphology of Cs partial layers, to be considered in future studies of Cs role in negative ion sources as well as in the ongoing quest to alternative catalyzers.

Temperature and Pressure Dependence of the Reaction S + CS (+M) → CS2 (+M).

Experimental data for the unimolecular decomposition of CS2 from the literature are analyzed by unimolecular rate theory with the goal of obtaining rate constants for the reverse reaction S + CS (+M) → CS2 (+M) over wide temperature and pressure ranges. The results constitute an important input for the kinetic modeling of CS2 oxidation. CS2 dissociation proceeds as a spin-forbidden process whose detailed properties are still not well understood. The role of the singlet-triplet transition involved is discussed.

Ultrafast dynamics and dissociative ionization of CS2 molecules studied via the femtosecond pump-probe method

The ultrafast dynamics and dissociative ionization of CS2 were studied using the pump-probe method with time-of-flight mass spectroscopy. The transient behavior of both parent ion (CS2 +) and fragment ions (S+ and CS+) was observed. It was found that all the ionic signals decay exponentially with lifetimes that were different for delay times, t>0 and t<0, which can be attributed to the evolution of different Rydberg states pumped by 267-nm and 400-nm laser pulses. The lifetimes of two Rydberg states were obtained simultaneously from one fitting of the transients. The fragment ions were produced by the dissociation of CS2 +, and it is suggested that the final ionic state is the C2Σg + state of CS2 + based on the measured S+/CS+ branching ratio. The S+/CS+ ratio is dependent on the delay time of the two lasers, indicating that the dissociation process of CS2 + is related to the evolution of the intermediate Rydberg state.

Reinvestigation of CS2 dissociation at 193 nm by means of product state-selective vacuum ultraviolet laser ionization and velocity imaging.

A branching ratio of 1.6 +/- 0.3 for S(3P)/S(1D) is obtained for the dissociation of CS2 with very low fluence 193 nm laser (less than 2 mJ/cm2), in which the S(3P) and S(1D) have been state-selectively ionized using VUV lasers at different wavelengths. The anisotropy parameters betamax(3P) = 0.8 and betamax(1D) = 1.9 indicate that these channels are preferentially populated at different geometries and the lifetime is very short.

Dynamics of the dissociative and nondissociative scattering of hyperthermal CS2+ from a self-assembled fluoroalkyl monolayer surface on gold substrate

Dissociative and nondissociative scattering of low energy CS2+ ions from a self-assembled monolayer surface of fluorinated alkylthiol [CF3(CF2)9CH2CH2SH] on vapor deposited gold has been studied using a modified crossed-beam instrument. Dissociation of CS2+ ions begins at ∼30 eV ion kinetic energy, much higher than the thermochemical threshold of 4.7 eV for the lowest energy dissociation channel forming S+. This product channel is dominant up to the ion energy of ∼50 eV, the highest energy accessible by this instrument. Both inelastically scattered parent ions and product ions leave the surface with very low kinetic energies, demonstrating that most of the ions’ kinetic energy is taken up by the surface rather than transferred into internal modes of recoiling ions. The scattered ion intensity maximum is found between the specular angle and the surface parallel. At all energies studied, primary ion intensity remains higher than that of fragment ions. Also, the intensity of S+ fragment ions is higher than that of CS+ fragment ions, suggesting that the distribution of internal excitation of the recoiling CS2+ ions extends only slightly above the thresholds for the two product channels. A comparison of the relative intensities of the fragment ions with those from earlier collision-induced dissociation study of the CS2+ ions with xenon suggests that only ∼6.5 and ∼7.5 eV are transferred into internal modes for 30.6 and 49.8 eV energy collisions, respectively. This is lower than the energy transferred into internal modes in the gas phase collision-induced dissociation process, for which the center-of-mass collision energy is well defined. We infer from our observations that the effective mass of the surface collision partner is much less than that of the infinite mass which would apply to scattering from the gold substrate or the mass of the monolayer surface molecule. The experimental velocity vectors of scattered primary and fragment ions reveal that their maxima follow a circle whose center falls on the ion velocity vector, away from the laboratory collision center. From this collision center, we estimate the effective mass of the surface for surface-induced dissociation to be 150 corresponding to the CF3CF2CF end group of the SAM molecular chain.

à 2 Π u state-intermediated two-photon dissociation of CS2+ via the first channel

The [1+1] à 2Πu-state resonance enhanced two-photon dissociation process of CS2+ molecular ions has been investigated by measuring the photofragment S+ excitation (PHOFEX) spectrum in the wavelength range of 424–482 nm, where the CS2+ molecular ions were prepared purely by [3+1] multiphoton ionization of the neutral CS2 molecules at 483.2 nm. The PHOFEX spectrum was assigned essentially to the CS2+(à 2Πu)←CS2+(X̃ 2Πg) transition, and the dissociation mechanism of CS2+ was preliminarily attributed to (i) CS2+(X̃ 2Πg)→CS2+(à 2Πu) through one-photon excitation, (ii) CS2+(à 2Πu)→CS2+(X̃†) via internal conversion process due to the vibronic coupling between the à and X̃ states, (iii) CS2+(X̃†)→CS2+(B̃ 2Σu+) through the second photon excitation, and (iv) CS2+(B̃ 2Σu+)→S++CS owing to the potential curve crossing with the repulsive Σ−4 state correlated with the first dissociation limit.

Collision-induced dissociation of CS2+ to S2+ at kilovolt laboratory energies

Collision-induced dissociation (CID) of CS2 + molecular ions to S2 + ions at laboratory collision energies ranging from 1 to 6 keV energy has been studied by mass analyzed ion kinetic energy spectrometry (MIKES) utilizing a reversed geometry tandem mass spectrometer. The dissociation proceeds via four energetically distinct pathways which are strongly dependent upon the kinetic energy of the ion and on the nature of the collision gas. CID with argon neutrals is dominated at all energies by the lowest energy threshold reaction, which is endothermic by about 6 eV, whereas the energetics of the process differ and are strongly dependent on the ion kinetic energy when lighter collision gases (He, H2 and D2) are used for collisional activation. The most probable energy transfer from kinetic to internal modes is 11 ± 2 eV for these collision gases. A highly endothermic channel with kinetic energy loss of ~41 ± 4 eV opens up when the energy of the ions is reduced to 3 keV and less. At 1 keV ion energy, there is a small contribution to the total CID from a highly exothermic channel (kinetic energy release of 47 ± 5 eV) that is observed with all collision gases under low pressure conditions in the collision cell.

Resonance enhanced multiphoton ionization spectroscopy of carbon disulphide

Rydberg excited states of the CS2 molecule in the energy range 56 000–81 000 cm−1 have been further investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization (MPI) spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been aided by parallel measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. Thus we have been able to extend, and clarify, previous analyses of the tangled spin–orbit split vibronic structure associated with the 3Πu and 1Πu states derived from the configuration [2Πg]4pσu and the 3Δu, 1Δu, and 1Σ+u states resulting from the configuration [2Πg]4pπu, and to deduce an approximate wave number for the origin of the hitherto unidentified 3Σ+u state derived from this same configuration. Moving to higher energies we are able to locate, unambiguously, the origins of the next (n=5) members of four of these [2Πg]np Rydberg series, and to identify extensive series based on the presumed Rydberg configurations [2Πg]nsσg and [2Πg]nfλu with, in both cases, n≤10. We also identify MPI resonances attributable to CS(a 3Π) fragments, to ground state C atoms, and to S atoms in both their ground (3P) and excited (1S) electronic states. Analysis of the former resonances indicates that the CS(a 3Π) fragments resulting from two photon dissociation of CS2 at excitation wavelengths around 300 nm are formed with substantial rovibrational excitation.

Photooxidation of CS2 in the near‐ultraviolet and its atmospheric implications

Sequential two photon photolysis of CS2 is discussed. Experiments in our lab and others have shown that photolysis of CS2 and O2 mixtures with light of energies below the SC‐S bond dissociation energy produces OCS and SO2. We explain these results by the two photon sequential absorption and subsequent dissociation of CS2 to CS+S. The implications of this mechanism for the oxidation of CS2 in the atmosphere are discussed. Comparison to the currently accepted OH‐initiated oxidation mechanism suggests that the sequential two‐photon mechanism is too slow to be important in the atmosphere.

Lifetime of the (5S) state of sulphur studied by electron impact dissociation of CS2

The radiative lifetime of the forbidden transition 3p4 3P2–4s 5S20; λ1900.3 Å is measured by electron impact dissociative excitation of CS2. The present value (27 ± 5 μs) is compared with earlier experimental measurements and a recent theoretical calculation.

Vibrational Populations of CS(A1.PI.) Produced by Electron-Impact Dissociation of CS2 and OCS

The CS(A 1 Π-X 1 Σ + ) emission spectra produced by electron impact on CS 2 and OCS have been measured from threshold up to 120 eV. Emission cross sections of this band from CS 2 and OCS are 10±2 and (0.75±0.15) ×10 -18 cm 2 , respectively, at 100 eV. At low impact energies (below 20 eV), the vibrational state distributions of CS(A 1 Π, ν'=0-8) measured from CS 2 and OCS can be represented by temperatures of 12 500±2000 and 26 000±4000 K, respectively, while the rotational temperature of the ν'=0 level is estimated to be 3850± 400 K from both parents

Two-photon dissociation of CS2 in the 285–305 nm region

Abstract Photodissociation of carbon disulphide in the gas phase has been carried out in the 285–305 nm region using an excimer laser pumped (308 nm) dye laser. It was observed that CS 2 undergoes multiphoton excitation/dissociation and the photofragment S atoms and CS radicals were detected in the excited 3 1 D 2 and 3 1 S 0 and a 3 Π states respectively by the REMPI technique (same colour). The observation of the photofragments in various energy states shows that photodissociation is taking place from more than one excited surface. The various photodissociation channels are discussed. It has been observed that CS 2 is excited to 3 d Rydberg states by two-photon excitation and the excited states of CS 2 have been tentatively assigned by correlation with the photoproducts.

Collision-induced dissociation of CS+2. Heat of formation of the CS radical

Guided-ion beam mass spectrometry is used to probe the reaction of CS+2 with Xe as a function of ion kinetic energy from thermal to 16 eV. S+, CS+, and Xe+ are the only observed reaction products. Formation of S+(4Su) is observed, even though it is spin forbidden, providing evidence for the importance of spin–orbit coupling in the dissociation of CS+2. The threshold for formation of S++CS, 4.74±0.04 eV, leads to a heat of formation of the CS radical ΔfH00(CS) of 65.8±0.9 kcal/mol. From this value, we derive the bond energies D00(CS)=169.8±0.9 kcal/mol, D00(S–CS)=103.8±0.9 kcal/mol, and D00(O–CS)=158.7±0.9 kcal/mol. The onset for production of CS+ by collision-induced dissociation of CS+2 is observed at 6.16±0.07, 0.40 eV above the thermodynamic threshold, but coincident with the threshold for excitation to the C̃ state of CS+2. The cross section for charge transfer to form Xe+ displays a threshold of ≊2 eV, corresponding to the difference in ionization energies of Xe and CS2. This process is significantly enhanced at higher energies where the concomitant dissociation of CS2 to CS and S becomes accessible.