- Infrared laser kinetic spectroscopy of a photofragment CS generated by photodissociation of CS2 at 193 nm: Nascent vibrational-rotational- translational distribution of CS
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Carbon monosulfide fragments generated by CS2 photodecomposition at 193 nm were examined by time-resolved observation of their vibration-rotation spectral lines with infrared diode laser kinetic spectroscopy.The CS molecules were found to be initially spread over a wide range of vibrational and rotational levels which were accessible with available energy, for both the triplet and singlet channels leading to sulfur atoms in the 3P ground and 1D excited states, respectively.The analysis of the observed line shape has allowed us to obtain information also on translational energy of CS fragments and to distinguish the contributions of the two channels.The branching ratio was thus estimated to be approximately one to one.
- Kanamori, Hideto,Hirota, Eizi
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- Millimeter-wave-detected, millimeter-wave optical polarization spectroscopy
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We report a new form of microwave optical double-resonance spectroscopy called millimeter-wave-detected, millimeter-wave optical polarization spectroscopy (mmOPS). In contrast to other forms of polarization spectroscopy, in which the polarization rotation of optical beams is detected, the mmOPS technique is based on the polarization rotation of millimeter waves induced by the anisotropy from optical pumping out of the lower or upper levels of the millimeter wave transition. By monitoring ground-state rotational transitions with the millimeter waves, the mmOPS technique is capable of identifying weak or otherwise difficult-to-observe optical transitions in complex chemical environments, where multiple molecular species or vibrational states can lead to spectral congestion. Once a transition is identified, mmOPS can then be used to record pure rotational transitions in vibrationally and electronically excited states, with the resolution limited only by the radiative decay rate. Here, the sensitivity of this nearly-background-free technique is demonstrated by optically pumping the weak, nominally spin-forbidden CS e Σ-3 -X Σ+1 (2-0) and d Δ3 -X Σ+1 (6-0) electronic transitions while probing the CS X Σ+1 (v″ =0, J″ =2-1) rotational transition with millimeter waves. The J′ =2, N′ =2← J′ =1, N′ =1 pure rotational transition of the CS e Σ-3 (v′ =2) state is then recorded by optically preparing the J′ =1, N′ =1 level of the e Σ-3 (v′ =2) state via the J′ =1, N′ =1← J″ =1 transition of the e Σ-3 -X Σ+1 (2-0) band.
- Steeves, Adam H.,Bechtel, Hans A.,Coy, Stephen L.,Field, Robert W.
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- The proton Affinity of CS
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We have studied the reactivity of HCS(1+) ions with several molecules at 300 K using a SIFT apparatus.The measured rate coefficients for the proton-transfer reactions of HCS(1+) with C2H5OH and CH3SH are appreciable fractions of their respective collosional rate coefficients and from this we deduce that the proton affinity of CS is 188.2 +/- 1 kcal mol-1.This value differs from the literature value by some 13 kcal mol-1 but is in close agreement with a very recent theoretical value.
- Smith, D.,Adams, N. G.
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- Fast Flow Studies of Atomic Carbon Kinetics at Room Temperature
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The reactions of atomic carbons with OCS, NO, O2, N2O, SO2, and H2S were studied at room temperature in a fast flow reactor.The atomic carbon, which was obtained from the microwave dissociation of CO diluted in He, was homogeneously mixed with the reactant molecules in a section of flow tube far from the discharge.The pseudo-first-order decay of atomic carbon was determined from the decay of CS ultraviolet chemiluminescence produced by the C + OCS reaction.As electronically excited CS is rather long-lived, it is shown how long-lived chemiluminescence can be used for obtaining kinetic data.In flow experiments, the rigorous determination of pseudo-first-order reaction rate constants is given by solving the differential continuity equation of the decaying reactive species in the flow.However, in most studies such an effort is not undertaken and rate constants are determined assuming plug flow for the reactive species because it allows an easy conversion of decay distances into reaction times.In the present study both approaches have been used.The plug-flow rate constant values were found to be significantly smaller than those given by the solution of the continuity equation.Our study thus provides a new example of the danger of the plug-flow approximation when conditions justifying it are not fulfilled.Specifically, the plug-flow assumption requires low homogeneous and wall-depletion rates of the reactive species with respect to its diffusion rate in the carrier gas.In our experiments none of these conditions was fulfilled and, in particular, the atomic carbon wall removal was found to be very efficient.Rate constants were determined for the first time for the reactions with OCS, SO2, and H2S.For the reactions with O2, NO, and N2O, previous studies, essentially performed by flash photolysis, gave a large scatter of data.Our values do not match any of those data.However agreement for relative rate coefficients is found with Husain's latest values, obtained at the lowest flash-lamp energy, which are furthermore the closest to ours.Our reaction rate constant values, given by the solution of the continuity equation of the atomic carbon in the flow, are (in 10-11 cm3 molecule-1 s-1 units): 10.1 +/- 0.7 with OCS; 2.7 +/- 0.2 with NO; 1.6 +/- 0.2 with O2; 0.85 +/- 0.16 with N2O; 6.9 +/- 1.7 with SO2; and 8.3 +/- 1.8 with H2S.
- Dorthe, G.,Caubet, Ph.,Vias, Th.,Barrere, B.,Marchais, J.
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- A 193 nm laser photofragmentation time-of-flight mass spectrometric study of CS2 and CS2 clusters
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A crossed laser and moleucular beam photofragmentation apparatus is described.The apparatus is equipped with a rotatable molecular beam source and a translationally movable ultrahigh vacuum mass spectrometer for time-of-flight (TOF) measurements.Using this apparatus we have measured the TOF spectra of S and CS resulting from the photofragmentation processes, CS2 + hν(193 nm) -> CS(X,v) + S(1D or 3P).The translational energy distributions of photofragments derived from the S and CS TOF spectra are in good agreement.This observation, together with the finding that the TOF spectra of S and CS are independent of laser power in the 25-150 mJ range, shows that the further absorption of a laser photon by CS to form C(3P) + S(3P) within the laser pulse is insignificant.The TOF spectra of S obtained at electron ionization energies of 20 and 50 eV are indiscernible, indicating that the contribution to the TOF spectrum of S from dissociative ionization of CS is negligible at electron impact energies 50 eV.The thermodynamical thresholds for the S(1D) and S(3P) channels are determined to be 18.7 and 45.0 +/- 0.4 kcal/mol, respectively, consistent with literature values.Structures found in the translational energy distribution can be correlated with vibrational structures of CS(X,v = 0-5) associated with the S(1D) channel.The translational energy distribution supports the previous observation that the vibrational state distribution of CS(X,v) is peaked at v = 3.The TOF experiment is also consistent with the S(3P)/S(1D) ratio of 2.8 +/- 0.3 determined in a recent vacuum ultraviolet laser induced fluorescence measurement on the S photofragment.Photofragments from CS2 clusters are observed at small laboratory angles with respect to the CS2 beam direction and are found to have velocity distributions peaked at the CS2 cluster beam velocity.
- Tzeng, W.-B.,Yin, H.-M.,Leung, W.-Y.,Luo, J.-Y.,Nourbakhsh, S.,et al.
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- Gas-Phase Reactions of H3Si- and Me3Si-. The formation of Si-O and Si-S Bonds. A Flowing Afterglow and ab Initio Study
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The ions H3Si- and Me3Si- undergo Si-O and/or Si-S bond forming reactions with CO2, COS, CS2, SO2, N2O, MeNCO, and MeNCS forming H3SiO3-, Me3SiO-, H3SiS-, or Me3SiS- ions as appropriate.The rates of these reactions vary markedly, e.g., the reaction of H3Si- with CS2 (to form H3SiS- + CS) occurs at every encounter, whereas that of H3Si- with N2O (to form H3SiO- plus N2) occurs for only one in every thousand collisions.Ab initio calculations (at 6-31G level) for the reactions of H3Si- with CO2, CS2, SO2, and N2O suggest different and complex reaction pathways.The reaction of H3Si- with CO2 is characterized by initial approach to carbon, and subsequent rearrangements are required to form H3SiO-.H3SiS- is formed by a simple path from CS2 following initial attack at sulfur.H3Si- reacts with SO2 in alternative ways to form five-coordinate intermediate which subsequently decomposes to H3SiO- plus SO.H3Si- is likely to attack N2O at the terminal nitrogen, and subsequent rearrangement forms H3SiO-.The length, or complexity of the reaction pathway appears inversely related to the measured efficiency in the majority of reactions.
- Sheldon, John C.,Bowie, John H.,DePuy, Charles H.,Damrauer, Robert
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- Mechanism and Product Energy Disposal in the Reaction of Ar(1+)(2P3/2) with CS2(X1Σg(+)
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The reaction of Ar(1+) with CS2 is investigated at thermal and near thermal energies by using both tandem ion cyclotron resonance (ICR) spectroscopy and kinetic energy ICR.At thermal energies the absolute rate constant is measured to be 2.9*10-10 cm3/s, and the ionic product branching ratio to be 97 percent S(1+) and 3 percent CS2(1+).Kinetic energy studies revealed the CS2(1+) product is 90 percent formed in the A2Π state with a near Franck-Condon vibrational state distribution and 10 percent in the X2Π state.The S(1+) product is formed exclusively in the ground S(1+)(4S) state with the maximum kinetic energy allowed by energy and momentum conservation.The implication is the originating Ar(1+)/CS2 charge transfer takes place via a long-range electron jump since no momentum transfer occurs (in contrast to the formation of CS2(1+) (A2Π), where substantial momentum trasfer occurs).These data strongly suggest the S(1+)(4S) product arises from nascent CS2(1+)(B2Σu(+)) that is rapidly predissociated by the 4Σ-state that leads to S(1+)(4S)/CS(X1Σ(+)) products.The crossing of the two states must occur very near the recombination energy of Ar(1+) (ca. 15.7 eV).This interpretation is consistent with known CS2(1+)(B2Σu(+)) radiative lifetimes and theoretical spin-orbit induced coupling between similar states in CO2(1+).The data and interpretations are compared to those in the literature where available.
- Rincon, Marina E.,Pearson, John,Bowers, Michael T.
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- Photoionization dynamics in CS fragmented from CS2 studied by high-resolution photoelectron spectroscopy
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The photoionization dynamics of CS have been studied using high-resolution laser photoelectron spectroscopy. The photodissociation of CS2 at ~308 nm results in highly rotationally excited CS in its X 1∑+ singlet ground state, as well as in rotationally cold CS in the excited a3Π triplet state. The ground-state CS fragments are formed together with sulfur in its 3P, 1D, and 1S electronic states; triplet CS is produced in coincidence with ground-state sulfur (3P). In both channels the photoelectron spectra are dominated by Δν = 0 propensity, but transitions involving Δν = 1 and 2 are also observed.
- Rijs, Anouk M.,Backus, Ellen H.G.,De Lange, Cornelis A.
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- Photopolymerization of liquid carbon disulfide produces nanoscale polythiene films
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Broad band solar or 300-400 nm irradiation (Hg-Xe arc source) of liquid-phase carbon disulfide produces a new carbon-sulfur polymer with the approximate (n = 1.04-1.05) stoichiometry (CSn)x. The polymer, from here on called (CS)x, forms as a ~200 nm thick transparent golden membrane as measured by SEM and AFM techniques. IR spectra for this polymer show some similarities with those obtained for the gas-phase photopolymerized (CS2)x and the high-pressure-phase polymer of CS2, called Bridgman's Black. The observed FT-IR absorptions of (CS)x include prominent features at 1431 (s, br), 1298 (m), 1250 (ms), and 1070 cm-1 (m). In contrast to previous proposals for (CS2)x, 13C labeling and model compound studies of α-(C3S5)R2 and β-(C3S5)R2 (R = methyl or benzoyl) suggest that the absorption at 1431 cm-1 and those at 1298 and 1250 cm-1 are indicative of carbon-carbon double bonds and carbon-carbon single bonds, respectively. The molecular structure of α-(C3S5)(C(O)C6H 5)2, determined at -84 °C, belongs to space group P1, with a = 7.486(5) A, b = 13.335(11) A, c = 17.830(13) A, α = 105.60(6)°,β = 95.32(6)°, γ = 90.46(6)°, Z = 4, V = 1706(2) A,3, R= 0.0785, and Rw = 0.2323. With use of electron and chemical ionization mass spectrometry, C4S6 and C6S7 were identified as the dominant soluble molecular side-products derived from a putative ethylenedithione (S=C=C=S) precursor. Atomic force microscopy (AFM) provided surface topology information for the thin film (CS)x and revealed features that suggested the bulk material is formed from small polymer spheres 20-50 nm in size. Both (CS2)x and (CS)x are extensively cross-linked through disulfide linkages and both materials show strong EPR resonances (g > 2.006) indicative of sulfur-centered radicals from incomplete cross-linking. A polymerization mechanism based on the intermediacy of S2C=CS2 is proposed.
- Zmolek,Sohn,Gantzel,Trogler
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- Coaxial measurement of the translational energy distribution of CS produced In the laser photolysis of CS2 at 193 nm
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Carbon disulfide (CS2) photolysis was investigated in the gas phase using an argon fluoride (ArF) laser at 193 nm.The coaxial time-of-flight (TOF) distributions of CS radicals produced in the photolysis have been measured.Photochemical fragments have been observed with translational energies below 3 kcal/mol.The vibrational distribution of the CS fragments was also probed by laser induced fluorescence (LIF), and these measurements confirm that significant amounts of CS radicals are produced in vibrational levels greater than v" = 6.From a computer simulation of the experimental LIF data, a vibrational distribution was also obtained.Vibrational levels up to v" = 12 were found to be populated in a bimodal distribution, which peaks at v" = 4, and extends to v" = 12.There was a significant amount of rotational excitation of nascent CS produced in high vibrational levels of the ground state.The disjoint translational energy and CS vibrational energy distributions can be used to obtain an estimate of the S(3P) to S(1D) ratio of 0.66.
- McCrary, V. R.,Lu, R.,Zakheim, D.,Russell, J. A.,Halpern, J. B.,Jackson, W. M.
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- Production and IR absorption of cyclic CS2 in solid Ar
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Linear carbon disulfide (denoted as SCS) isolated in solid N2 or Ar at 13 K was irradiated with light at 193 nm from an ArF excimer laser. In addition to an absorption line of CS at 1277.4 cm-1, new lines at 881.3 and 520.9 cm-1 were observed after photolysis of SCS in solid N2. These lines are assigned to cyclic CS2 (denoted cyc-CS2) based on results from 34S- and 13C-isotopic experiments. Doublet lines of cyc-CS2 at 876.5 (881.1) and 517.7 (522.7) cm-1 were observed after irradiation of SCS in solid Ar at 193 nm; lines in parentheses are associated with a minor matrix site. Secondary photolysis at 248, 308, 532, 560, or 580 nm diminishes signals of cyc-CS2 and produces SCS. Theoretical calculations using MP2-full and density-functional methods (BLYP and B3LYP) predict three isomers of CS2: SCS, cyc-CS2, and linear CSS; relative energies, structures, vibrational wavenumbers, and IR intensities were predicted for each isomer. Cyc-CS2 has C-S bonds (~1.74 A) elongated relative to those of SCS (~1.56 A), a S-S bond ~2.14 A, and angleSCS ? 76°; it lies ~73 kcal mol-1 above SCS. Calculated vibrational wavenumbers, IR intensities, and isotopic shifts for cyc-CS2 fit satisfactorily with experimental results. An asymmetric transition State Connecting SCS and cyc-CS2 is characterized, yielding a ring-opening barrier of ~24.4 kcal mol-1 (zero-point energy corrected). Photoconversion between linear and cyclic CS2 in a matrix cage is discussed.
- Bahou, Mohammed,Lee, Yu-Chang,Lee, Yuan-Pern
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- Energy distribution of the fragments produced by photodissociation of CS2 at 193 nm
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Gaseous CS2 was dissociated at 193 nm into CS and S.The translational and internal energy distributions of the CS fragments were measured.There is now overwhelming evidence that the upper electronic state S3 is predissociative.In fact there are three upper states of importance, the initially excited S3, a state which dissociates to CS(X1Σ) and S(1D) and a triplet state which dissociates to CS(X1Σ) and S(3P).The CS fragments were rotationally excited withy an average rotational energy ca.3.5 kcal/mole.The vibrational populations were also strongly inverted for both the 1D and the 3P dissociations and their surprisal plots were linear.CS fragments were found with v7.Of the dissociations resulting in CS fragments with v6, 80 +/-10percent of the S atoms are produced in the 1D state and 20 +/-10percent in the 3P state.
- Yang, S. C.,Freedman, A.,Kawasaki, M.,Bersohn, R.
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- Mass spectrometric study of the photoionization of CS. The dissociationenergy of the CS molecule
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A mass spectrometric study of the photoionization of CS provides 11.319+/-0.006 eV for the ionization potential, in agreement with literature values. Three Rydberg series converging to the C(2)Σ(+) state of the molecular ion are identified. Their limit is 18.003+/-0.006 eV. The threshold for dissociative ionization of CS towards S(+) is located at 70.05+/-0.1 nm and yields D(0)(CS, 0 K)= 709.4 +/- 2.5 kJ/mol. This result is briefly compared with prior data. D(0)(CS, 0 K)=709.6+/-1.2 kJ/mol and D(0)(CS(+), 0 K)=617.1+/-1.3 kJ/mol are selected as the best estimatesfor these quantities.
- Coppens, P.,Drowart, J.
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- Matrix isolation and spectroscopic properties of the methylsulfinyl radical CH3(O)S
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The atmospherically highly relevant methylsulfinyl radical CH 3(O)S was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH 3(O)S and its D3- and 13C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.
- Reisenauer, Hans Peter,Romanski, Jaroslaw,Mloston, Grzegorz,Schreiner, Peter R.
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supporting information
p. 9467 - 9469
(2013/10/01)
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- UV-induced transformations of matrix-isolated 1,3,4-thiadiazole-2-thiones
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Monomers of 5-mercapto-1,3,4-thiadiazole-2-thione (bismuthiol) were studied using an experimental matrix-isolation technique as well as by carrying out theoretical quantum chemical calculations. The calculations, performed using the quadratic configuration interaction method with single and double excitations (QCISD)/6-31++G(d,p)//DFT(B3LYP)/ 6-311 ++G(2d,p), predict that the thione-thiol tautomer of bismuthiol should be significantly (by more than 19 kJ mol-1) more stable than other tautomeric forms. Accordingly, only the signatures of the thione-thiol tautomer were observed in the FT-IR spectrum of bismuthiol, recorded directly after deposition of an Ar matrix. UV (l> 320 nm) irradiation induced the conversion of the thione-thiol tautomer into the dithiol form. Analogous investigations were carried out for two related compounds: 5-methyl-1,3,4-thiadiazole-2-thione and 5-methylthio-1,3,4-thiadiazole-2-thione. For these two species, only the thione tautomeric forms were observed after deposition of Ar matrices. These tautomers were predicted (by QCISD calculations) to be more stable (by at least 19kJmol-1) than other tautomeric forms. Upon UV irradiation, the most stable thione forms of these compounds were transformed into the corresponding thiol tautomers. Direct observation of the thione! thiol phototautomeric processes provides a clear proof that intramolecular proton transfer reaction can occur in molecules, such as bismuthiol, in spite of the increased NH...S distance, in comparison to other phototautomerizing species studied so far. All the isomers of the studied compounds (substrates and products of the photoreactions) were identified by comparison of their IR spectra with the spectra calculated at the DFT(B3LYP)/6-311 ++G(2d,p) level of theory for possible isomeric structures. Copyright
- Rostkowska, Hanna,Lapinski, Leszek,Nowak, Maciej J.
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experimental part
p. 56 - 66
(2010/07/08)
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- Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy
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A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2 CS and N2 or C O2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. Therotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observati on; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and C S2 are discussed.
- Chu, Li-Kang,Han, Hui-Ling,Lee, Yuan-Pern
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- Isomers of OCS2: IR absorption spectra of OSCS and O(CS 2) in solid Ar
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Irradiation of an Ar matrix sample containing O3 and CS 2 with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm-1; numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO2. Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm-1. The first set of lines are assigned to CS stretching, O-S stretching, and S-C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to CO stretching and OCS bending modes of dithiiranone, O(CS2), respectively, based on results of 34S- and 18O-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS2: O(CS 2), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS2) has a cyclic CS2 moiety and is the most stable isomer of OCS2. OSCS is planar, with bond angles OSC?111.9° and SCS?177.3°; it is less stable than SSCO and O(CS2) by ~102 and 154 kJ mol-1, respectively, and more stable than SOCS by ~26 kJ mol-1. Calculated vibrational wave numbers, IR intensities, 34S- and 18O-isotopic shifts for OSCS and O(CS2) fit satisfactorily with experimental results.
- Lo, Wen-Jui,Chen, Hui-Fen,Chou, Po-Han,Lee, Yuan-Pern
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p. 12371 - 12378
(2008/01/27)
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- Kinetics and mechanism for the oxidation of CS2 and COS at high temperature
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The rate constant for the thermal decomposition of CS2 and COS were investigated by measuring the time profiles of S atom using atomic resonance absorption spectroscopy behind the incident shock of CS2/Ar or COS/Ar mixtures, and the rate constants were determined to be k = (4.0 ± 0.1) × 1014 exp (-295 ± 20 kJ/RT) cm3 mol-1 s-1, T: 2200-2900 K and k = (1.4 ± 0.3) × 1015 exp (-290 ± 25 kJ/RT) cm3 mol-1 s-1, T: 2000-3200 K, respectively. The oxidation mechanism of COS was also investigated behind the incident shock of COS/O2/Ar mixtures and the rate constant for the reaction S + O2 → SO + O was obtained to be k = (9.5 ± 0.7) × 1013 exp (-41 ± 28 kJ/RT) cm3 mol-1 s-1, T: 2200-2900 K. From a numerical analysis for time profiles of S atom behind the incident shock of CS2/O2/Ar mixtures, the rate constant for the reaction O + CS → CO + S was expressed as k = (3.2 ± 1.0) × 1013 cm3 mol-1 s-1, T: 2100-3000 K. Similarly, the rate constant for the reaction CS + O2 → COS + O was also determined to be k = (6.1 ± 0.6) × 1012 exp (-51.0 ± 68 kJ/RT) cm3 mol-1 s-1, T: 2000-2900 K by measuring the time profiles of O atom behind the reflected shock of CS2/O2/Ar mixtures. Ab initio calculations were carried out and the reaction pathways of CS + O2 → COS + O and CS + O2 → CO + SO were also investigated.
- Murakami,Kosugi,Susa,Kobayashi,Fujii
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p. 1233 - 1240
(2007/10/03)
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- The formation of 1,2-propadiene-1,3-dithione (carbon subsulfide) from flash vacuum pyrolysis of 1,2-dithiole-3-thiones
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1,2-Propadiene-1,3-dithione (carbon subsulfide) has been obtained by flash vacuum pyrolysis of alkylthio substituted 1,2-dithiole-3-thiones in the temperature range 800-1000°C. The dithione was isolated and characterized in an argon matrix at 10 K.
- Pedersen, Carl Th.
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p. 4805 - 4808
(2007/10/03)
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- Evidence of a solvent-mediated barrier to radiationless decay in the (1A1) state of thiophosgene in solution
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Thiophosgene, Cl2CS, has been excitied in the near-uv and the resulting quantum yields of - fluorescence and of Cl2CS consumption have been measured as a function of solvent composition (perfluoro-n-hexane, n-hexane, CCl4), temperature, and excitation wavelenght.In agreement with previous work it is shown that (i) nonradiative processes dominate the decay of the state in solution, and (ii) perfluoroalkane solvents act as inert heat baths .The process by which the state is apparently quenched by CCl4 and n-hexane has been discovered.The nonradiative process leading to 's decay involves activation and crossing a barrier, the heigh of which is a function of the nature and composition of the solvent.CCl4 and n-hexane do not quench the excited state, but instead accelerate its rate of relaxation by lowering the barrier between the bound, radiative portion of the surface and a dark, unbound region.There is evidence that CCl4 or n-hexane form clusters around a Cl2CS solute molecule in mixed perfluoroalkane-CCl4 or n-hexane solutions.Barrier crossing leads to photodecomposition via at least two parallel paths, one free radical (Cl + ClCS) and the other likely molecular (CL2 + CS) the relative contributions of which are a function of excitation wavelenght. Key words: thiophosgene, photochemistry, solvent-mediated barrier crossing.
- Li, Jieming,Steer, Ronald P.
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p. 131 - 138
(2007/10/02)
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- Vibrational Populations of CS(A1II) Produced by Electron-Impact Dissociation of CS2 and OCS
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The CS(A1II-X1Σ+) emission spectra produced by electron impact on CS2 and OCS have been measured from threshold up to 120 eV.Emission cross sections of this band from CS2 and OCS are 10 +/- 2 and (0.75 +/- 0.15) * 10-18 cm2, respectively, at 100 eV.At low impact energies (below 20 eV), the vibrational state distributions of CS(A1II, ν'=0-8) measured from CS2 and OCS can be represented by temperatures of 12500 +/- 2000 and 26000 +/- 4000 K, respectively, while the rotational temperature of the ν'=0 level is estimated to be 3850 +/- 400 K from both parents.Vibrational distribution data are approximately represented by distributions predicted from the impulsive half-collision model.
- Tokue, Ikuo,Kusakabe, Masanobu,Ogawa, Hiroshi,Ito, Yoshio
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p. 3588 - 3591
(2007/10/02)
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- Production and reactions of triplet CS: Matrix infrared and ultraviolet spectra of C2S2
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Matrix infrared and visible-ultravioiet absorption spectroscopy and ab initio electronic structure calculations have been used to characterize the reaction products from a Tesla coil Ar/CS2 discharge. The discharge is an excellent source of CS, which reacts with other molecules to form the major C3S2 product and the transient C2S2 species. The spectra of discharged mixed isotopic samples Ar/12CS2/13CS2 and Ar/C32S2/C34S2 exhibit triplet patterns in the CS antisymmetric stretching region, which unambiguously identifies the new C2S2 molecule with two equivalent CS subgroups. The magnitudes of the 12,13 C and 32,34S isotopic shifts further characterize the diatomic CS subgroup nature of C2S2. Another product contains two equivalent CS subgroups interacting with inequivalent S atom(s). The formation of C2S2 (3∑) from the simple CS2 discharge requires triplet CS. Evidence was also obtained for other transient cumulene species.
- Bohn, Robert B.,Hannachi, Yacine,Andrews, Lester
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p. 6452 - 6459
(2007/10/02)
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- Heterocumulene, 8. - C4OS (4-Thioxo-1,2,3-butatrien-1-one),C4S2 (1,2,3-Butatriene-1,4-dithione) and C3S (3-Thioxo-1,2-propadienylidene) - Preparation and Spectroscopic Properties
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C4OS (8) is prepared by matrix photolysis and by flash pyrolysis of the precursor molecule 4, C4S2 (12) by matrixphotolysis of 10, 11, and 13.Upon irradiation both 8 and 12 are split reversibly into C3S (9) and CO or CS.The IR and UV/Vis spectra of C4OS(8), C3S(9), and C4S2 (12) are reported.Quantumchemical calculations have been performed for the structures, harmonic vibrational frequencies, singlet-triplet gaps, and electronic transition energies 8 and 12. Key Words: Matrix isolation / Photochemistry / Flash pyrolysis / Quantumchemical calculations
- Maier, Guenther,Schrot, Juergen,Reisenauer, Hans Peter,Janoschek, Rudolf
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p. 2617 - 2622
(2007/10/02)
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- Product energy disposal in the nonadiabatic reaction S(1D) + CS2 --> S2 (X3Σ-g) + CS (X1Σ+)
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The product energy disposal in the reaction S(1D) + CS2 --> S2 +CS is measured via laser-induced fluorescence.Molecular sulphur is produced exclusively in its electronic ground state (3Σ-g) with up to 3 quanta of vibrational excitation and rotational excitation that roughly approximates a 1000 K Boltzmann distribution.The CS produced from the reaction is formed predominantly in its vibrationless state.The total internal energy content of the product molecular sulphur is only about 12percent of the total available energy of the reaction: the CS fragment also has minimal internal energy, implying that most of the reaction energy resides in product translation.These results are different from those observed in the isovalent S + OCS reaction and suggest that a different detailed mechanism is operative.
- Sapers, Steven P.,Andraos, Nancy,Donaldson, D.J.
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p. 1738 - 1745
(2007/10/02)
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- Two-Photon Photochemistry of CS2: Formation of S2 (v2) and CS(v10) at 308 nm
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Room-temperature CS2 is photolyzed at 308 nm in a low-pressure flow cell.Laser-excited fluorescence is used to observe both CS(v10) and S2(v2) products 10μs after the excimer laser pulse.Both products display a quadratic dependence on the excimer laser intensity.These results are consistent with a two-photon excitation of CS2 to a high-lying electronic state (near 154 nm) which predissociated to S and CS, followed by reaction of the S atom with undissociated CS2.
- Sapers, S. P.,Donaldson, D. J.
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p. 8918 - 8921
(2007/10/02)
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- Gas-Phase Reactions of Fe(1-) and Co(1-) with Simple Thiols, Sulfides, and Disulfides by Fourier Transform Mass Spectrometry
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Fe(1-) and Co(1-) are found to react with simple thiols, sulfides, and disulfides.The primary reaction products formed from these metal anions, M(1-), and thiols include MS(1-), MSH(1-), and MSH2(1-) and suggest a mechanism involving initial insertion of the metal into the weak C-S bond.Similarly, C-S insertion is the main mode of attack in the reactions with the sulfides and disulfides, in analogy to what is observed for the reaction of metal cations.Collision-induced dissociation is used to support the proposed structures for the primary products, H-Fe(1-)-SH andFe(1-)-SH.Some of the thermochemical data derived from this study include D0(M(1-)-S)>103 kcal/mol and D0(M(1-)-SH)=83 +/- 9 kcal/mol.Finally, a brief survey of the reactivity of V(1-), Cr(1-), and Mo(1-) with selected organosulfur compounds is also reported.
- Sallans, L.,Lane, K. R.,Freiser, B. S.
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p. 865 - 873
(2007/10/02)
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- Reactions of Thiophene and Alkylthiophenes in Glow Discharge
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The glow discharge reaction of thiophene is shown to produce thioketene and carbon monosulfide along with other gaseous products.The dominant liquid product is ethynylthiophene.Methylthiophenes and especially dimethylthiophenes produce benzene as one of the major liquid products.
- Skramstad, Jan,Chaudhry, Mohammed Shoaib,Garvang, Arne
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p. 509 - 512
(2007/10/02)
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- The photodissociation of thiophosgene at 248 nm
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A pulsed molecular beam of thiophosgene was photodissociated at 248 nm.The detection of CSCl and Cl2 fragments formed under collision free conditions is evidence for two decomposition pathways: (a) CSCl2 -> CSCl + Cl (b) CSCl2 -> CS(X1Σ) + Cl2.An estimate for the quantum yield for (a) is calculated to be 0.8 +/- 0.1.An impulsive spectator model is consistent with the measured translational energy distribution in process (a) for which on average 16 +/- 2 kcal/mol is found as translational energy.The results imply a vibrationally excited CSCl fragment.
- Ondrey, G. S.,Bersohn, R.
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p. 175 - 178
(2007/10/02)
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- CS+ (B2Σ+-X2Σ+) emission produced from Penning ionization of the CS(X1Σ+) radical
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Emission spectrum resulting from the energy transfer reaction of He (2 3S) with transient CS radical produced through a microwave discharge of Ar/CS2 mixture was observed in a flowing afterglow apparatus.A new CS+ (B2Σ+ -X2Σ+) band system due to He (23S)/CS Penning ionization was identified in the 220 - 340 nm region.The dominant bands were the (v',O) and (O, v'') progressions, which was consistent with the prediction from calculated Morse potential Franck-Condon factors.Although the observed bandhead wavelengths of the major CS+ (B-X) emission werein good agreement with those predicted from the reported spectroscopic data, the (4,0) band was located at an abnormal position.It was interpreted as a consequence of vibrational perturbation in the B2Σ+ state.The relative intensities of CS+(B-X), CS+(B-A), CI, and SI emission were estimated to represent that the dominant pathway of the He (23S)/CS reaction is Penning ionization.
- Tsuji, Masaharu,Obase, Hiroshi,Nishimura, Yukio
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p. 2575 - 2579
(2007/10/02)
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