SH Radicals Research Articles

Formation of carbonyl sulfide (OCS) via SH radicals in interstellar CO-rich ice under dense cloud conditions

Carbonyl sulfide (OCS) is widely observed in the gas phase toward star-forming regions and was the first of the only two sulfur-bearing species to be detected in interstellar ices so far. However, the chemical network governing its formation is still not fully understood. While the sulfurization of CO and the oxidation of CS are often invoked to form OCS other mechanisms could have a significant contribution. In particular, the multistep reaction involving CO and SH is a good candidate for forming a significant portion of the OCS in dense cloud environments. We aim to constrain the viability of the $ CO SH $ route for forming solid OCS in the interstellar medium, in a similar manner as $ CO OH $ is known to produce CO2 ice. This is achieved by conducting a systematic laboratory investigation of the targeted reactions on interstellar ice analogs under dense cloud conditions. We used an ultrahigh vacuum chamber to simultaneously deposit CO H2S and atomic H at 10 K. SH radicals produced in situ via hydrogen abstraction from H2S reacted with CO to form OCS . We monitored the ice composition during deposition and subsequent warm-up by means of Fourier-transform reflection absorption infrared spectroscopy (RAIRS). Complementarily, desorbed species were recorded with a quadrupole mass spectrometer (QMS) during temperature-programmed desorption (TPD) experiments. Control experiments were performed to secure the product identification. We also explored the effect of different H2S CO mixing ratios---with decreasing H2S concentrations---on the OCS formation yield. OCS is efficiently formed through surface reactions involving CO H2S and H atoms. The suggested underlying mechanism behind OCS formation is $ CO SH HSCO $ followed by $ HSCO H OCS H2 $. The OCS yield reduces slowly, but remains significant with increasing CO H2S mixing ratios ( CO H2S = 1:1, 5:1, 10:1, and 20:1). Our experiments provide unambiguous evidence that OCS can be formed from $ CO SH $ in the presence of H atoms. This route remains efficient for large H2S dilutions ($5<!PCT!>$ with respect to CO ), suggesting that it is a viable mechanism in interstellar ices. Given that SH radicals can be created in clouds over a wide evolutionary timescale, this mechanism could make a non-negligible contribution to the formation of interstellar OCS ice.

Sulfur release behavior and sulfur fixation mechanism during biomass microwave co-pyrolysis of Ascophyllum and rice straw

Co-pyrolysis with low-sulfur biomass is expected to improve the yield and quality of bio-fuels, without the usage of calcium-based desulfurizer. Sulfur transformation during microwave fluidized-bed co-pyrolysis between terrestrial and marine biomass (Ascophyllum, AS; Rice straw, RS) was investigated. Sulfur release was promoted during biomass co-pyrolysis, but it was inhibited during pyrolysis between AS and low-sulfur char. Thermal cracking of biomass was promoted during co-pyrolysis between biomass, accelerating the combination of H atoms and −SH radicals. Introduction of low-sulfur bio-char (CA) inhibited the generation of bio-char and the release of sulfur. Released sulfur was captured by –OH/C = C functional groups on bio-char through dehydration reactions/addition reactions, forming mercaptan in bio-char. Furthermore, introduction of microwave and bio-char promoted the cyclization and aromatization reaction, converting mercaptan to thiophene and improving the thermal stability of solid sulfur, and thus increasing in-situ sulfur fixation rate.

A Mechanism Study on the (+)-ESI-TOF/HRMS Fragmentation of Some PPI Prazoles and Their Related Substances.

Fragmentation mechanisms of some prazoles and their related substances were newly investigated in this paper via positive mode ESI-TOF HRMS1 and HRMS2. Some novel fragmentation rules or ions were found or detected in the research. The pyridine and the benzoimidazole ring remained in most cases during the ionization, and heterolytic fragmentations often occurred near the -S(O)nCH2- linker to give the [1,3]-H migration ion or [1,7]-H migration ion rearranging across the benzoimdazole ring. Smiles rearrangement ionizations also frequently occurred, initiated by the attack of the lone pair electrons from the pyridine ring, and the sulfones gave special N-(2-benzoimdazolyl) pyridine ions (11b and 12c) by a direct extraction from SO2, and the thioethers gave similar framework ions (8c, 9c and 10c) via the rearrangement and a further homolytic cleavage of SH radicals. However, the sulfoxides were seldom detected in the corresponding Smiles rearrangement ions during our measurement, and the N'-oxides of the pyridines did not undergo the Smiles rearrangement ionization due to the absence of the lone pair electrons. The 5/6-membered chelating ions with Na+ or K+ were frequently detected as the molecular and further fragment ions. Some novel and interesting fragment ions containing bivalent (8b and 9b), tetravalent (4b, 5c and 6c) or hexavalent (15b and 16b) sulfurs were first reported here.

Effect of carbon dioxide on oxy-fuel combustion of hydrogen sulfide: An experimental and kinetic modeling

CO2 is an important component in the acid gas and it is necessary to study the effect of CO2 presence on the oxy-fuel combustion of H2S with particular focus on the formation of carbonyl sulfide (COS). The oxy-fuel combustion of acid gas was conducted in a coaxial jet double channel burner. The distribution of flame temperature and products under stoichiometric condition along axial (R = 0.0) and radial at about 3.0 mm (R = 0.75) were analyzed, respectively. The Chemkin-Pro software was used to analyze the rate of production (ROP) for gas products and the reaction pathway of acid gas combustion. Both experimental and simulation results showed that acid gas combustion experienced the H2S chemical decomposition, H2S oxidation and accompanied by H2 oxidation. The CO2 presence reduced the peak flame temperature and triggered the formation of COS in the flame area. COS formation at R = 0.0 was mainly through the reaction of CO2 and CO with sulfur species, whereas at R = 0.75 it was through the reaction of CO with sulfur species. The ROP results indicated that H2 was mainly from H2O decomposition in the H2S oxidation stage, and COS was formed by the reaction of CO2 with H2S. ROP and other detailed analysis further revealed the role of H, OH and SH radicals in each stage of H2S conversion. This study revealed the COS formation mechanisms with CO2 presence in the oxy-fuel combustion of H2S and could offer important insights for pollutant control.

Ab Initio Microkinetics of H2S Interactions with Clean and Sulfided Au(110) at Low Temperature: A Strong Assistance in Partial Dissociation from Single Sulfur Atoms

A microkinetic model built on first-principles calculations is developed to clarify an ongoing experimental controversy regarding whether hydrogen sulfide (H2S) molecules are intact or dissociated on pristine and S-covered Au(110) surfaces at 120 K. From the simulation, we prove that only associative adsorption of H2S on the defect-free, flat (110) facet of gold occurs in the exposure region under investigation, whereas its reaction with sulfur adsorbed as single atoms straightforwardly proceeds to yield relatively strongly bound SH radicals for the surface precovered with elemental S. The sulfur assistance of neighboring H2S to decompose is ascribed to the stability of the corresponding transition state in which three-center hydrogen bonding interactions are being formed. One-dimensional zigzag chains of divalent sulfur are shown as structural units of the c(2 × 4) superstructure observed experimentally in inactive sulfur islands for the S + H2S reaction. The sensitivity of H–S bond cleavage in surface H2S to the aggregation state of coadsorbed sulfur may, in part, be rationalized by the change in valency of these adatoms. This is the first time that a clear theoretical picture of the chemistry of H2S on such an open Au surface is provided, which is beneficial to elucidate more complicated reaction processes, such as sulfur-poisoning tolerance of gold nanocatalysts.

Rate Coefficients of the Reactions of Fluorine Atoms with H2S and SH over the Temperature Range 220-960 K.

Reaction F + H2S→SH + HF (1) is an effective source of SH radicals and an important intermediate in atmospheric and combustion chemistry. We employed a discharge-flow, modulated molecular beam mass spectrometry technique to determine the rate coefficient of this reaction and that of the secondary one, F + SH→S + HF (2), at a total pressure of 2 Torr and in a wide temperature range 220-960 K. The rate coefficient of Reaction (1) was determined directly by monitoring consumption of F atoms under pseudo-first-order conditions in an excess of H2S. The rate coefficient of Reaction (2) was determined via monitoring the maximum concentration of the product of Reaction (1), SH radical, as a function of [H2S]. Both rate coefficients were found to be virtually independent of temperature in the entire temperature range of the study: k1 = (1.86 ± 0.28) × 10-10 and k2 = (2.0 ± 0.40) × 10-10 cm3 molecule-1 s-1. The kinetic data from the present study are compared with previous room temperature measurements.

The role of highly vibrationally excited H2 initiating the nitrogen chemistry

The formation of hydrides by gas-phase reactions between H2 and a heavy element atom is a very selective process. Reactions with ground-state neutral carbon, oxygen, nitrogen, and sulfur atoms are very endoergic and have high energy barriers because the H2 molecule has to be fragmented before a hydride bond is formed. In cold interstellar clouds, these barriers exclude the formation of CH, OH, NH, and SH radicals through hydrogen abstraction reactions. Here we study a very energetically unfavorable process, the reaction of N(4S) atoms with H2 molecules. We calculated the reaction rate coefficient for H2 in different vibrational levels, using quantum methods for v = 0−7 and quasi-classical methods up to v =12; for comparison purposes, we also calculated the rate coefficients of the analogous reaction S (3P)+ H2(v) → SH + H. Owing to the high energy barrier, these rate coefficients increase with v and also with the gas temperature. We implemented the new rates in the Meudon photodissociation region (PDR) code and studied their effect on models with different ultraviolet (UV) illumination conditions. In strongly UV-irradiated dense gas (Orion Bar conditions), the presence of H2 in highly vibrationally excited levels (v ≥ 7) enhances the NH abundance by two orders of magnitude (at the PDR surface) compared to models that use the thermal rate coefficient for reaction N(4S) + H2 → NH + H. The increase in NH column density, N(NH), across the PDR is a factor of ~25. We investigate the excitation and detectability of submillimeter NH rotational emission lines. Being a hydride, NH excitation is very subthermal (Trot ≪ Tk) even in warm and dense gas. We explore existing Herschel/HIFI observations of the Orion Bar and Horsehead PDRs. We report a 3σ emission feature at the ~974 GHz frequency of the NH NJ = 12 − 01 line toward the Bar. The emission level implies N(NH) ≃ 1013 cm−2, which is consistent with PDR models using the new rate coefficients for reactions between N and UV-pumped H2. This formation route dominates over hydrogenation reactions involving the less abundant N+ ion. JWST observations will quantify the amount and reactivity of UV-pumped H2 in many interstellar and circumstellar environments.

Successive H-atom Addition to Solid OCS on Compact Amorphous Solid Water

Abstract Carbonyl sulfide (OCS) is an abundant sulfur (S)-bearing species in the interstellar medium. It is present not only in the gas phase, but also on interstellar grains as a solid; therefore, OCS very likely undergoes physicochemical processes on icy surfaces at very low temperatures. The present study experimentally and computationally investigates the reaction of solid OCS with hydrogen (H) atoms on amorphous solid water at low temperatures. The results show that the addition of H to OCS proceeds via quantum tunneling, and further addition of H leads to the formation of carbon monoxide (CO), hydrogen sulfide (H2S), formaldehyde (H2CO), methanol (CH3OH), and thioformic acid (HC(O)SH). These experimental results are explained by our quantum chemical calculations, which demonstrate that the initial addition of H to the S atom of OCS is the most predominant, leading to the formation of OCS-H radicals. Once the formed OCS-H radical is stabilized on ice, further addition of H to the S atom yields CO and H2S, while that to the C atom yields HC(O)SH. We have also confirmed, in a separate experiment, the HC(O)SH formation by the HCO reactions with the SH radicals. The present results would have an important implication for the recent detection of HC(O)SH toward G+0.693–0.027.

Removal of impurities from waste tire pyrolysis char using the molten salt thermal treatment

Thermo-chemical recycling of waste tire to generate pyrolytic char as alternative carbon black is a promising route for waste disposal and environmental sustainability. However, impurities in waste tire (like Zn, Si, Ca and S) are probably enriched in the pyrolytic char, and removal of those impurities is of great importance for char recycling. To avoid generating large amount of waste acids and polluted gases in the traditional impurities removing process, molten salt (Na2CO3-NaOH) thermal treatment was creatively proposed in the current work. The influence of operational temperatures (in the range of 350 to 450 °C) was investigated in relation to the efficiency of impurity removal. Results show that the removal efficiency of impurity components was firstly increased but then weakened by increasing treating temperature from 350 to 450 °C, while the highest removal rate was obtained at 400 °C. Generally, the current system could effectively remove more than 80% of ash and 70% of sulfur at 400 °C, with the recovery rate of char between 71% and 83%. Specifically, calcium carbonate/sulfate was removed from the char due to its good solubility in the molten salts. In addition, molten salts showed good activity to convert char contained inorganic sulfides and ·SH radicals into salts-soluble Na2S. Similarly, silicon and zinc were tended to be transformed into soluble silicate and zincate, which had higher solubility in the used molten salt. In addition, the agglomerated char particles were separated into smaller and more uniform size during molten salt thermal treatment.

Transformation of nitrogen, sulfur and chlorine during waste tire pyrolysis

The transformation of N/S/Cl during pyrolysis of waste tire were investigated by Thermogravimetry-Mass Spectrum (TG-MS) and flow tube furnace reactor. The pyrolysis of waste tire included four stages, i.e., dehydration below 200 ℃, decomposition of tire additives at 200∼300 ℃, degradation of natural rubber at 300∼420 ℃, and cracking of synthetic rubber at 420∼500 ℃. The activation energy Eα were calculated according to the Coats-Redfern integral method, ca. 154.72∼158.23 and 200.46∼231.58 kJ/mol for degradation of natural rubber and synthetic rubber, respectively. Most of nitrogen (60.32∼67.78 wt.%), sulfur (56.73∼62.38 wt.%), and chlorine (58.60∼64.92 wt.%) were remained in the pyrolytic char. For the pyrolytic oil composition, expect for alkanes, alkenes, aromatic hydrocarbons, and oxygenates, the S-containing disulfide and sulfurous acid ester, N-containing quinoline and pyrimidine diamine, and Cl-containing silane, dichlorododecylmethyl- were detected. The nitrogen, sulfur, and chlorine in pyrolytic gas had diverse types. The N-containing pollutants mainly derived from inorganic ammonium and heterocyclic-N. NH3 had a wide releasing temperature range, while NO, HCN, and HNCO were mainly generated at 300∼600 °C. The C–S and -SH radicals mainly contributed to S-containing pollutants, i.e., H2S, COS, CS2, SO2, CH3SH, and C6H5SH. The Cl-containing pollutants exhibited dominant release within the temperature range of 300∼600 °C. Overall, higher heating rate promoted gas emissions, especially for NO, HCN, CH3SH, and HCl. This article provides basic knowledge on hazardous N/S/Cl transformation in solid char, liquid oil, and gas during pyrolysis of waste tire that will provide valuable information for future control technologies of pollutants emission.

Searches for Interstellar HCCSH and H2CCS

Abstract A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, , is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10−9–10−10. We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.

Conflict in the Mechanism and Kinetics of the Barrierless Reaction between SH and NO2 Radicals.

There are some unsettled issues regarding the mechanism and kinetics of an important atmospheric reaction of NO2 radical with the SH radical. The existing mechanism is based on the formation of HSO and NO radicals, both of which can result only along one barrierless channel. However, the detection of NO radical has never been reported though the formation of HSO radical has been followed in some studies to determine the rate constants. The latter are mainly obtained by monitoring the SH decay, but rate constants are reported to be highly conflicting among the existing studies reporting its value ranging from 10-10 to 10-12 cm3 molecule-1 sec-1. The present work attempts to resolve these issues by exploring various reaction pathways through the global reaction route mapping of the potential energy surface at the level of spin-unrestricted and spin-restricted coupled-cluster and density functional theories. The initial association of two radicals was found to proceed via two barrierless modes: (1) S-N association leading to HSNO2 and, (2) S-O association resulting in HSONO, in particular the cis-isomer. The kinetics of the barrierless pathways was investigated through rate constants computed using canonical variational transition state theory (CVTST) along with their temperature and pressure dependence investigated using the master equation. The rate constants calculated using spin-unrestricted methods are found to be in agreement with experimentally observed range of rate constant, and the formation of cis-HSONO (via mode 2) is observed to be the main contributing channel. Contrary to the results of spin-restricted calculations, the barrierless channel (mode 1) leading to the formation of HSNO2 is predicted to involve two bottlenecks when results using spin-unrestricted calculations were analyzed. Notably, the spin-unrestricted calculations predict a prereaction complex for the formation of S-N bond (via mode 1) which has been treated using Miller's unified transition state theory with a two transition state model. The fate of all the species involved in the reaction is critically evaluated in the present work, and the predictions made can be a subject of further experimental and theoretical studies involving radical-radical reactions.

A Coupled Cluster Investigation of SNO Radical Isomers and Their Reactions with Hydrogen Atom: Insight into Structures, Conformers, Barriers, and Energetics.

High-level coupled cluster theory with single and double excitation, and including a perturbative triples correction (CCSD(T)) method and a series of Dunning's augmented correlation consistent basis sets, aug-cc-pVXZ (X = D, T, Q, and 5) was applied to examine the conformational landscape of SNO radical system. The basis set has an important effect on the relative stability of SNO radical isomers; that is, at the CCSD(T)/aug-cc-pV5Z level of theory, the NSO radical is the most stable member of SNO radical family. This is in contrast to previous density functional theory prediction suggesting SNO radical is the most stable isomer. The CCSD(T)/aug-cc-pV5Z//CCSD(T)/aug-cc-pVTZ results suggest that the reaction between SNO radical isomers and hydrogen atom result in the formation of their [H,N,S,O] hydrides with HNSO hydrides being the most stable ones. Subsequently, these hydrides could decompose either into SH and NO radicals or into SN and OH radicals. The former pathway is preferred due to relatively lower barriers and favorable reaction energies. The results from our calculations support the role of S-nitrosothiols as NO shuttling agent in signaling-pathways and as a new source of HS and NO radicals in the lower atmosphere of Venus. Overall, these high-level calculations will play an important role in improving our understanding about the chemistry of S-nitrosothiols that has recently become a topic of interest because of their involvement in biochemical pathways and planetary processes.

Magnetic trapping of SH radicals.

Magnetic trapping of SH radicals, produced via the photostop technique, has been demonstrated. H2S in a skimmed, supersonic molecular beam was photodissociated at 212.8 nm to produce SH inside a 330 mK deep static magnetic trap. The molecular-beam speed was controlled by the mixing ratio of H2S in Kr to match the recoil velocity of the SH photofragments such that some SH radicals were produced with near-zero laboratory-frame velocity. The density of SH radicals in the 2Π3/2, v = 0, J = 3/2 state was followed by (2 + 1) REMPI over seven orders of magnitude of signal intensity. 5 ms after photodissociation, SH radicals moving faster than the capture velocity of 13 m s-1 had left the trap. The 1/e trap lifetime of the remaining SH radicals was 40 ± 10 ms at an estimated density of 5 × 104 molecules per cm3. Photostop offers a simple and direct way to accumulate absolute ground state molecules in a variety of traps.

Inhibition and Promotion of Pyrolysis by Hydrogen Sulfide (H2S) and Sulfanyl Radical (SH).

This study resolves the interaction of sulfanyl radical (SH) with aliphatic (C1-C4) hydrocarbons, using CBS-QB3 based calculations. We obtained the C-H dissociation enthalpies and located the weakest link in each hydrocarbon. Subsequent computations revealed that, H abstraction by SH from the weakest C-H sites in alkenes and alkynes, except for ethylene, appears noticeably exothermic. Furthermore, abstraction of H from propene, 1-butene, and iso-butene displays pronounced spontaneity (i.e., ΔrG° < -20 kJ mol-1 between 300-1200 K) due to the relatively weak allylic hydrogen bond. However, an alkyl radical readily abstracts H atom from H2S, with H2S acting as a potent scavenger for alkyl radicals in combustion processes. That is, these reactions proceed in the opposite direction than those involving SH and alkene or alkyne species, exhibiting shallow barriers and strong spontaneity. Our findings demonstrate that the documented inhibition effect of hydrogen sulfide (H2S) on pyrolysis of alkanes does not apply to alkenes and alkynes. During interaction with hydrocarbons, the inhibitive effect of H2S and promoting interaction of SH radical depend on the reversibility of the H abstraction processes. For the three groups of hydrocarbon, Evans-Polanyi plots display linear correlations between the bond dissociation enthalpies of the abstracted hydrogens and the relevant activation energies. In the case of methane, we demonstrated that the reactivity of SH radicals toward abstracting H atoms exceeds that of HO2 but falls below those of OH and NH2 radicals.

α-Hydrogen Abstraction by •OH and •SH Radicals from Amino Acids and Their Peptide Derivatives.

We have used computational quantum chemistry to investigate the thermochemistry of α-hydrogen abstraction from the full set of amino acids normally found in proteins, as well as their peptide forms, by •OH and •SH radicals. These reactions, with their reasonable complexity in the electronic structure (at the α-carbon), are chosen as a consistent set of models for conducting a fairly robust assessment of theoretical procedures. Our benchmarking investigation shows that, in general, the performance for the various classes of theoretical methods improves in the order nonhybrid DFT → hybrid DFT → double-hybrid DFT → composite procedures. More specifically, we find that the DSD-PBE-P86 double-hybrid DFT procedure yields the best agreement with our high-level W1X-2 vibrationless barriers and reaction energies for this particular set of systems. A significant observation is that, when one considers relative instead of absolute values for the vibrationless barriers and reaction energies, even nonhybrid DFT procedures perform fairly well. To exploit this feature in a cost-effective manner, we have examined a number of multilayer schemes for the calculation of reaction energies and barriers for the abstraction reactions. We find that accurate values can be obtained when a "core" of glycine plus the abstracting radical is treated by DSD-PBE-P86, and the substituent effects are evaluated with M06-2X. Inspection of the set of calculated thermochemical data shows that the correlation between the free energy barriers and reaction free energies is strongest when the reactions are either endergonic or nearly thermoneutral.

Unimolecular Rate Constants for the HF and HCl Elimination Reactions from Chemically Activated CF2ClSH

ABSTRACTChemically activated CF3SH, CFCl2SH, and CF2ClSH were formed through combination of SH and CF3, CFCl2, and CF2Cl radicals, respectively. The SH radical was prepared by abstraction of an H‐atom from H2S by the halocarbon radical produced during photolysis of (CF3)2C=O, (CFCl2)2C=O, or (CF2Cl)2C=O. 1,2‐HX (X = F, Cl) elimination reactions were observed from CF3SH, CFCl2SH, and CF2ClSH with products detected by GC‐MS. The combination reaction of CF2Cl radicals with SH radicals prepared CF2ClSH molecules with approximately 318 kJ/mol of internal energy. The experimental rate constants for elimination of HCl and HF from CF2ClSH were 3 ± 3 × 1010 and 2 ± 1 × 109 s−1, respectively. Comparison to Rice–Ramsperger–Kassel–Marcus (RRKM) calculated rate constants assigned the threshold energies as 171 ± 12 and 205 ± 12 kJ/mol for the unimolecular elimination of HCl and HF, respectively. Theoretical calculations using the B3PW91, MP2, and M062X methods with the 6311+G(2d,p) and 6‐31G(d',p') basis sets established that for a specific method the threshold energies differ by only 4 kJ/mol between the two different basis sets. There was wide variation among the three methods, but the M062X approach appeared to give threshold energies closest to the experimental values. Chemically activated CF3SH and CFCl2SH were also prepared with about 318 kcal mol−1 of internal energy, and the HX (X = F, Cl) elimination reactions were observed. Only HCl loss was detected from CFCl2SH, but the rate was too fast to measure with our kinetic method; however, based on our detection limit the HF elimination channel is at least 50 times slower.

Synthesis, structure, and sunlight photolysis of benzyl- and tert-butyl-substituted octamethyltitanocene dihydrosulfides

New titanocene dihydrosulfide compounds [(C5Me4CH2Ph)2Ti(SH)2] (6) and [(C5Me4t-Bu)2Ti(SH)2] (7) were obtained by addition of hydrogen sulfide to the corresponding doubly tucked-in titanocenes, and titanocene hydrosulfide compounds [(C5Me4CH2Ph)2TiSH] (8) and [(C5Me4t-Bu)2TiSH] (9) by H2S-induced protonolysis of σ-Ti–C bonds in [(η5-C5Me4CH2Ph)Ti(III)(η5:η1-C5Me4CH2-o-C6H4)] and [(C5Me4t-Bu)Ti(III)(η5:η1-C5Me4CMe2CH2)], respectively. The crystal structures of 6, 8, and 9 and electronic absorption spectra of 6–9 in hexane solution highly resemble those of corresponding [Cp*2Ti(SH)2] (1) and [Cp*2TiSH] (2), however, compounds 6 and 7 strongly differ in their sensitivity to sunlight mutually and with respect to 1. The sunlight photolysis of 6 in toluene proceeded similarly to the process described previously for 1 except that about three times longer exposition (300 h) was required to obtain the cyclopentadienyltitanium sulfide cage cluster [{(C5Me4CH2Ph)Ti}4S6] (10) in 48% yield. In contrast, compound 7 photo-decomposed very efficiently to give compound 9 as the only isolated titanium-containing product in 87% yield. The formation of 10 can be accounted for the redox elimination of the cyclopentadiene followed by elimination of hydrogen sulfide in intramolecular condensation reaction whereas the formation of 9 requires the dissociation of SH radicals. Both the processes were recognized by Rosenthal and Beweries to concur in photodecomposition of [Cp*2Ti(OH)2].

New investigation on THz spectra of OH and SH radicals (X[formula omitted

Pure rotational transitions of OH and SH radicals have been recorded in the THz spectral range using cw-THz and synchrotron-based FT-FIR techniques. Line lists on these radicals have been completed in the three and two lowest vibrational states for OH and SH, respectively. Furthermore, the hyperfine structure of OH and SH has been observed for the first time using infrared IR FT-spectroscopy, and at frequencies higher than 1THz, respectively. A combined fit has been made for each of these radicals including v=0, 1 and 2 for OH and v=0 and 1 for SH.

Doppler limited rotational transitions of OH and SH radicals measured by continuous-wave terahertz photomixing

Abstract A continuous-wave terahertz (CW-THz) source generated by photomixing has been employed to detect and quantify radicals produced in a cold plasma probing their spin-rotation transitions. Due to their dual interest for both atmospherists and astrophysicists, the hydroxyl OH and the mercapto SH radicals have been chosen. The photomixing technique which can access the largest range of THz frequencies of any known coherent source, allowed to resolve the Doppler-limited hyperfine transitions of OH in the 2.5 THz frequency region. Line profile analysis of the hyperfine components demonstrated that OH radicals have been detected in this region at a ppm level at a temperature close to 490 K. The hyperfine structure of SH has been resolved for the first time above 1 THz. Ten new frequency transitions have been measured in the 1.3–2.6 THz frequency range using the CW-THz synthesizer based on a frequency comb. With relative uncertainties better than 10 −7 , the CW-THz frequencies measured in this study are now competitive with those measured by other instruments such as frequency multiplication chains or FT-FIR spectrometers and are now capable to improve the predictions of the complete high-resolution spectra of these radicals collected in the atmospheric and astrophysical spectroscopic databases. versioncorrigeeAC 2011-07-18 17:32 © 2011 Arnaud Cuisset.