2944-05-0Relevant articles and documents
Infrared laser kinetic spectroscopy of a photofragment CS generated by photodissociation of CS2 at 193 nm: Nascent vibrational-rotational- translational distribution of CS
Kanamori, Hideto,Hirota, Eizi
, p. 3901 - 3905 (1987)
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.
Millimeter-wave-detected, millimeter-wave optical polarization spectroscopy
Steeves, Adam H.,Bechtel, Hans A.,Coy, Stephen L.,Field, Robert W.
, (2005)
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.
The proton Affinity of CS
Smith, D.,Adams, N. G.
, p. 3964 - 3965 (1985)
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.
Fast Flow Studies of Atomic Carbon Kinetics at Room Temperature
Dorthe, G.,Caubet, Ph.,Vias, Th.,Barrere, B.,Marchais, J.
, p. 5109 - 5116 (1991)
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.
A 193 nm laser photofragmentation time-of-flight mass spectrometric study of CS2 and CS2 clusters
Tzeng, W.-B.,Yin, H.-M.,Leung, W.-Y.,Luo, J.-Y.,Nourbakhsh, S.,et al.
, p. 1658 - 1669 (1988)
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.
Gas-Phase Reactions of H3Si- and Me3Si-. The formation of Si-O and Si-S Bonds. A Flowing Afterglow and ab Initio Study
Sheldon, John C.,Bowie, John H.,DePuy, Charles H.,Damrauer, Robert
, p. 6794 - 6800 (1986)
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.
Mechanism and Product Energy Disposal in the Reaction of Ar(1+)(2P3/2) with CS2(X1Σg(+)
Rincon, Marina E.,Pearson, John,Bowers, Michael T.
, p. 4290 - 4294 (1988)
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.
Photoionization dynamics in CS fragmented from CS2 studied by high-resolution photoelectron spectroscopy
Rijs, Anouk M.,Backus, Ellen H.G.,De Lange, Cornelis A.
, p. 744 - 749 (2004)
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.
Photopolymerization of liquid carbon disulfide produces nanoscale polythiene films
Zmolek,Sohn,Gantzel,Trogler
, p. 1199 - 1207 (2001)
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.
Coaxial measurement of the translational energy distribution of CS produced In the laser photolysis of CS2 at 193 nm
McCrary, V. R.,Lu, R.,Zakheim, D.,Russell, J. A.,Halpern, J. B.,Jackson, W. M.
, p. 3481 - 3490 (1985)
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.
