Electron-attachment spectroscopy: formation and dissociation of negative ions in the fluorochloroethylenes

The formation and dissociation of negative ions in C₂Cl₄, C₂FCl₃, 1,1-C₂F₂Cl₂, 1,2-C₂F₂Cl₂ (isomeric mixture), C₂F₃Cl and C₂F₄ have been studied employing (dissociative) electron-attachment spectroscopy with nearly monoenergetic electrons in the energy range 0–15 eV. All six compounds show low-lying resonances (below 4eV) associated with various dissociation channels leading to one negative and one neutral fragment. It is found that the resonance energy increases if Cl is replaced by F. Electron affinities in the limit of the unknown excess energy are given for the radicals C₂Cl₃, C₂F₂Cl₂, C₂F₂Cl and C₂F₃. For C₂Cl₄ and C₂F₂Cl₂ long-lived parent molecular anions are observed. Only tetrafluoroethylene gives fragments by cleavage of the double bond, as a result of the perfluoro effect.     

Carbon-13 enrichment by IR laser chemistry of CHF3-Cl2

IR laser chemistry of CHF₃ is investigated in both neat form and in the presence of Cl₂ for carbon-13 enrichment. Infrared multiple-photon dissociation of CHF₃ is an order of magnitude more efficient in the scavenged system compared to the neat case. The photolysis of CHF₃/Cl₂ mixture results in two products, viz., CF₂Cl₂ and C₂F₄Cl₂ but with different enrichment factors. The parametric studies show that C₂F₄Cl₂ arises due to MPD of CF₂Cl₂ in secondary photolysis.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

13C-selective two-stage IRMPD of mixtures of CHClF2 and HI

The ¹³C-selective infrared multiple-photon decomposition (IRMPD) of mixtures of CHClF₂ and HI was examined in collimated and focused beam geometries using a CO₂TEA laser. The carbon-containing products were CH₂F₂ and CHF₂I. The former product showed remarkably high ¹³C atom concentrations beyond 95% under selected experimental conditions, while the latter contained 25% or less. The observed results can be explained satisfactorily in terms of the consecutive two-stage IRMPD process occurring in a single irradiation procedure, where the first-stage IRMPD of natural CHClF₂ produces ¹³C-enriched CHF₂I via the insertion of the initial decomposition fragment CF₂ into HI, and the second stage is the subsequent ¹³C-selective IRMPD of the CHF₂I to form a CHF₂ radical and an I atom. The CHF₂ radical reacts with HI to form CH₂F₂. Decomposition probabilities of ¹²CHClF₂ and ¹³CHClF₂ were measured as a function of laser fluence to optimize enrichment conditions. Furthermore, partial decomposition probabilities or relative production yields were measured as functions of laser line, pressure of HI, and pressure of CHClF₂. Both stages showed high ¹³C selectivities in the irradiation with the laser radiation around 1040 cm^–1 and at fluences below 4 J cm^–2. This mixture is one of the most promising chemical systems for the production of highly enriched ¹³C.     

The 2ν1, 2ν2 and 2ν3 overtones of FClO3

The infrared spectra of the 2ν₁, 2ν₂ and 2ν₃ overtones of perchloryl fluoride, FClO₃, have been recorded at high resolution using monoisotopic pure samples. Four symmetric top species have been investigated: F³⁵Cl¹⁶O₃, F³⁷Cl¹⁶O₃, F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃. The v_i = 2, i = 1, 2, 3 vibrationally excited states are totally symmetric, so these overtones correspond to parallel bands of medium/weak intensity, centered from 2010 to 2120 cm⁻¹ (2ν₁), from 1390 to 1430 cm⁻¹ (2ν₂) and from 1070 to 1100 cm⁻¹ (2ν₃). Most of the bands are unperturbed and their analysis was straightforward. The band origins, the rotational and centrifugal molecular constants in the v₁ = 2, v₂ = 2 and v₃ = 2 states have been determined, with standard deviations of the fits from 0.00024 to 0.00067 cm⁻¹. The 2ν₁ overtones of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃ are perturbed by an A₁/E Coriolis resonance between the v₁ = 2 state and one E component of the v₄ = 1, v₆ = 2 manifold. The 2ν₂ of F³⁷Cl¹⁸O₃ is perturbed by the same kind of interaction involving the v₁ = v₆ = 1 (E) state, at about 1396 cm⁻¹. In these bands the resonance is localized on rotational levels with specific J and K values. As a consequence, a few transitions of the perpendicular bands involving the interacting levels could be identified in the spectra. A simultaneous fit of the transitions assigned to the dyads has been performed and the parameters of the excited states have been determined, including the high order Coriolis interaction coefficient . The anharmonic constants x₁₁, x₂₂, x₃₃ of all the studied isotopologues of FClO₃, x₄₆ of F³⁵Cl¹⁶O₃, x₄₆ + g₄₆ of F³⁷Cl¹⁶O₃ and x₁₆ of F³⁷Cl¹⁸O₃, have been derived.     

The ν4 and ν2 + ν5 high resolution infrared bands of FClO3 and FClO3

The high resolution infrared spectra of monoisotopic F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃ have been studied in the region of the ν₄ fundamentals, centered at 1278.3 and 1263.3 cm⁻¹, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν₂ + ν₅ combination bands, centered at 1270.7 cm⁻¹ in F³⁵Cl¹⁸O₃ and 1257.3 cm⁻¹ in F³⁷Cl¹⁸O₃. In particular, they affect the kl > 0 levels of the v₄ = 1 and v₂ = v₅ = 1 states which cross at kl ? 18 in F³⁵Cl¹⁸O₃ and kl ? 3 in F³⁷Cl¹⁸O₃, due to the opposite values of and . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F³⁵Cl¹⁸O₃, while in F³⁷Cl¹⁸O₃ only the Δl = Δk = ±2 one is active. In the spectrum of F³⁵Cl¹⁸O₃ 3423 transitions have been assigned, 10% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants between the v₄ = 1 and v₂ = v₅ = 1 levels have been obtained. The depertubed band origins of ν₄ and ν₂ + ν₅ are 1277.310567(165) and 1271.753733(195) cm⁻¹, respectively, and the anharmonic resonance constant is 2.804416(153) cm⁻¹. For F³⁷Cl¹⁸O₃, 3022 transitions have been assigned, 38% belonging to the ν₂ + ν₅ combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm⁻¹, for ν₄and ν₂ + ν₅ and the constant is 2.9350669(405) cm⁻¹. The equilibrium geometry of perchloryl fluoride, r_e (ClO) = 139.7(3) pm, r_e (ClF) = 161.0(5) pm, and α_e (OClO) = 115.7(4) degree, has been determined using the A_e and B_e equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F^35/37Cl¹⁶O₃ and F^35/37Cl¹⁸O₃.     

Enrichment of 13C by IRMPD of CBr2F2

The CO₂-laser-induced infrared multiple photon decomposition of natural CBr₂F₂ in the presence of oxygen has been examined as a function of pulse number (30–1500), reactant pressures (CBr₂F₂, 10–150 Torr and O₂, 5–90 Torr), laser line [9P(8)–9P(32)], and laser fluence (1–3 J cm^–2) to optimize irradiation conditions for ¹³C-enrichment. CF₂O was the main carbon containing product and afterwards was converted into CO₂ via hydrolysis. A small amount of C₂Br₂F₄ was detected only under extreme conditions, for example, at high laser fluences or wavenumbers close to an absorption band. The ¹³C-atom fraction of the final product CO₂ was found to be 20–80%, depending on experimental conditions. The two-stage IRMPD process proposed previously has been examined in further detail in the present study. First, CBr₂F₂ containing about 30% of ¹³C was prepared in the ¹³C-selective IRMPD of natural CHClF₂ in the presence of Br₂. The second-stage IRMPD of the CBr₂F₂ in the presence of oxygen under selected conditions resulted in the high enrichment of ¹³C beyond 90%.     

A polarized CARS investigation of the fine structure population inversion of Cl atoms from laser photolysis of ICl and the quenching of Cl(2 P 1/2) by O2

The time resolved polarized CARS technique has been used to detect Cl atoms produced by photolysis of ICl in the presence and absence of O₂. A population inversion was observed between the ground state electronic levels Cl(² P _1/2) and Cl(² P _3/2). The rate constant for Cl(² P _1/2) decay (quenching + reaction) in ICl was determined to be (3.2±0.2)×10^–13 cm³/molecule×s; the rate constant for Cl(² P _3/2) reaction with ICl was determined to be (7.8±0.5)×10^–12 cm³/molecule×s; and the rate constant for Cl(² P _1/2) quenching by O₂ was determined to be (1.9±0.2)×10^–13 cm³/molecule×s.     

First-stage enrichment in CO2-laser-induced13C separation by a two-stage IRMPD process: IRMPD of CHClF2/Br2 mixtures

We have been studying the practical CO₂-laser-induced¹³C separation by a two-stage IRMPD process. The IRMPD of natural CHClF₂ in the presence of Br₂ mainly produced CBr₂F₂, which was found to be highly enriched with¹³C. The yield and¹³C-atom fraction of CBr₂F₂ were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br₂ pressure using a CO₂ TEA laser with an output less than 1 J pulse^–1 in order to optimize experimental conditions for¹³C separation. For example, we obtained CBr₂F₂ at a¹³C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF₂ and 10-Torr Br₂ with the laser radiation at a wavenumber of 1045.02 cm^–1 and at a fluence of 3.4 J cm^–2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10^–4 g of¹³C-enriched CBr₂F₂ (¹³C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher¹³C by the second-stage IRMPD of the CBr₂F₂ in the presence of oxygen.     

Isotopically selective CVD of silicon by IRMPD of Si2F6

The IRMPD of Si₂F₆ by a CO₂ TEA laser was applied to isotopically selective CVD of silicon. A white film, probably consisting of polymers of SiF₂, was deposited on a metal foil during the irradiation of natural Si₂F₆ with the laser radiation at 951.19 cm^–1 and about 1.5 J cm^–2. Upon heating, the film became dark brown, evolving SiF₄. The³⁰Si content was found to be as high as about 20%.     

LiF-LiCl-B2O3系统非晶态快离子导体结构的研究

本文通过对¹¹B核磁共振(¹¹B-NMR)、红外光谱等实验方法,研究了LiF-LiCl-B₂O₃三元系统玻璃的结构和离子导电性,着重于F^-离子在玻璃网络中所起的作用,以及F^-,Cl^-和Li⁺离子对导电率的影响。LiF-LiCl-B₂O₃三元系统玻璃,随LiF含量的增加,B由三角体向四面体变化,从而F^-离子进入网络,使玻璃结构由[B₂O₃]三角体层状结构向三维空间延展,形成了含有[BO₃F]基团的三维空间网络,Cl^-离子以游离的离子存在于网络中,起着松散网络的作用,对提高电导率有利,而Li⁺离子作为传导离子,对电导率的贡献是主要的。本系统玻璃的电导率是随LiF,LiCl含量的增加而增大,在300℃时测得电导率σ=6.12×10^-4Ω^-1·cm^-1。 关键词：     

Optical limiting behavior of new fullerene derivatives

The optical limiting behavior of C₆₀Ph₅Cl, C₆₀Cl₆, and C₇₀Cl₁₀ in toluene solution has been measured at 532 nm with nanosecond pulses. The limiting threshold for C₆₀Ph₅Cl, C₆₀Cl₆, and C₇₀Cl₁₀ were 4, 8, and 8 J/cm², respectively. The limiting action was strongly influenced by the number of conjugated double bonds and the nature of the ligand. Both lower limiting thresholds and throughputs make these new fullerene derivative compounds good promising candidates for optical limiting materials in the toluene solution.     

Measurements of nitrogen-broadening coefficients in the ν3 band of the hydroperoxyl radical using a continuous wave quantum cascade laser

Mid-infrared absorption spectroscopy was applied to the detection of the hydroperoxyl radical (HO₂) in pulsed laser photolysis combined with a laser absorption kinetics reactor. The transition of the ν₃ vibrational band assigned to the O-O stretch mode around 1065 cm⁻¹ was probed with a thermoelectrically cooled, continuous wave, mid-infrared, distributed feedback quantum cascade laser (QCL). The HO₂ was generated through 355 nm photolysis of Cl₂/1,4-c-C₆H₈/O₂ mixtures. The mid-infrared absorption spectrum of the HO₂ radical was recorded between 1064 and 1065.5 cm⁻¹. The absorption line shapes were well represented by the Voigt profile. The nitrogen-broadening coefficients of the HO₂ radical at 295 K were determined for four absorption lines around 1065 cm⁻¹. Mid-infrared absorption detection using a QCL as a spectroscopic light source is a powerful method in spectroscopic and kinetics studies of the HO₂ radical.     

Intensity studies in Raman effect

The dependence of the relative intensities of Raman lines, having different polarisation characters, on the mode of excitation has been studied using unpolarised, horizontally and vertically polarised incident light. Standard intensities have been obtained in the cases of CCl₄, CHCl₃, C₆H₆, C₂Cl₄, C₂H₂Cl₂, C₂H₄Cl₂, C₆H₅Cl, C₆H₅CH₃ and C₆H₅CH₂OH with the intensity of the 458 cm^?1 line of CCl₄ as standard and from these, the values ofα′, the derived polarisability, have been obtained in the case of total symmetric lines characteristic of particular bonds and certain conclusions regarding the intensity variations of corresponding lines in the different liquids have been arrived at. Values of derived anisotropy have also been obtained in the case of the depolarised lines relative to that of 313 cm^?1 line in CCl₄.     

EPR study on the chemistry and photochemistry of copper(II) dithiocarbamate mixed-ligand complexes

The thermal and photochemical reactions of the 1∶1 mixed-ligand complexes Cu(dtc)X (X=Cl^?, NO₃ ^?, ClO₄ ^?) have been studied on the ground of their EPR spectra in acetone, CCl₄/i-PrOH (1∶1), and CHCl₃/i-PrOH (1∶1) solutions. The study allows us to get some insight into the behaviour of the mixed-ligand Cu^II(dtc)X complexes with respect to the acceptor properties of halocarbons. In CCl₄/i-PrOH (1∶1) both Cu^II(dtc)⁺…NO₃ ^? and Cu^II(dtc)⁺…ClO₄ ^? undergo thermal reactions within their donor-acceptor complexes with CCl₄ to yield Cu(dtc)Cl. On the time scale of the experiment the reaction does not occur thermally in CHCl₃/i-PrOH (1∶1), but occurs photochemically in both halocarbon/i-PrOH (1∶1) systems in which Cu(dtc)Cl is further photolyzed to CuCl₂. Continuous photolysis of the title compounds in acetone simply bleaches the solution without any intermediate EPR or light absorption.     

On the direct formation of HO2 radicals after 248 nm irradiation of benzene C6H6 in the presence of O2

We present in this work the direct observation of HO₂ radicals after irradiation of benzene C₆H₆ at 248 nm in the presence of O₂. HO₂ radicals have been unambiguously identified using the very selective and sensitive detection of continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled to a laser photolysis reactor. HO₂ radicals were detected in the first vibrational overtone of the OH stretch at 6638.20 cm^-1, using a DFB diode laser. This reaction might be important because 248 nm photolysis of H₂O₂ has often been used in the past for studying the OH^•-initiated degradation of C₆H₆, often using a large excess of C₆H₆ over H₂O₂. The possible importance of the title reaction with respect to these former laboratory studies has been quantified through comparison with HO₂ ^• signals obtained from 248 nm photolysis of H₂O₂: one obtains under our conditions (excess O₂ and total pressure of 6.6 kPa helium) from the 248 nm irradiation of identical initial concentrations [C₆H₆]=[H₂O₂] the following relative initial radical concentrations: [HO₂ ^•]=(0.28±0.05)×[OH^•]. Experiments with various O₂ concentrations have revealed that the origin of the HO₂ radicals is not the reaction of H-atoms with O₂, but must originate from the reaction of O₂ with excited C₆H₆ ^*. The quantum yield of C₆H₆ ^* formation has been deduced to ϕ=0.2±0.1. PACS  42.62.Fi; 82.20.Pm; 82.33.Tb     

Photoabsorption cross sections for chlorinated methanes and ethanes between 46 and 100 Å

Photoabsorption cross sections for the methanes CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, CHClF₂, CHCl₂F and the ethanes C₂F₆, C₂ClF₅, C₂Cl₂F₄ were measured between 46 and 100 Å. In particular, the 0.2 Å resolution provides some insight into the Cl 2p absorption process. It is noted that the molecular cross section for all 8 Cl-containing gases display an L edge “discontinuity” of 3.55±0.15 Mb per Cl atom. The experimental molecular cross sections are compared with sums of atomic cross sections at 100 Å using both theoretical and empirical atomic values. The sums of theoretical atomic cross sections describe every experimental molecular value to better than 10%. The sums of empirical atomic cross sections describe molecular values to within 2%.     

Isotopically selective infrared multiphoton dissociation of 2-chloro-1,1,1-trifluoroethane: 13C selectivity and mechanism

13 C-selective infrared multiphoton dissociation of CF₃CH₂Cl has been studied by analyzing the distribution of ¹³C concentrations of the main products CF₂=CHCl, CF₂=CH₂, CF₂=CHF, C₂F₆, and the trace products CF₃CH₂CF₃ and CF₃CH=CHF₃. The mechanism mainly concerns the dissociation of energized CF₃CH₂Cl, the collisional stabilization of excited CF₃CH and CF₃CH₂ and the recombination of the nascent radicals. No significant radical–molecule reactions degrade the intrinsic ¹³C dissociation selectivity. High ¹³C production yield and ¹³C concentration can be attained at a laser fluence of 1.6 J/cm². Such low fluence can be used to improve focus condition and enhance photon utilization efficiency for practicable ¹³C separation. Received: 10 March 1998/Revised version: 17 September 1998     

Energy transfer and upconversion of Nd doped RbY2Cl7

Single crystals of Nd³⁺:RbY₂Cl₇ were grown by the Bridgman-Stockbarger method. The host crystal contains two slightly inequivalent Y³⁺ ions, each with an approximate C_2v site symmetry. Anti-Stokes emission from the ⁴G_7/2 and ⁴D_3/2 levels was observed after laser excitation of the ⁴F_3/2 and ⁴F_9/2 multiplets. Laser excitation at 413 cm⁻¹ or 453 cm⁻¹ above the ⁴F_3/2 multiplet resulted in emission from the ²P_1/2 level. Laser site-selective upconverted emission spectra have been measured, as well as their emission transients and power dependence. Possible excited state absorption and energy-transfer upconversion (ETU) mechanisms are proposed and discussed. Due to the smaller crystal field and a somewhat different energy level structure for the Nd³⁺ ions in RbY₂Cl₇ as compared with those observed for Nd³⁺ in fluoride or oxide hosts, the ⁴G_7/2 and ⁴D_3/2 multiplets are populated under ⁴F_3/2 excitation in a three and four step ETU process, respectively, instead of in a two and three step process as observed for the lighter hosts.     

Intermediate particles in the catalysis of radical reactions of chlorohydrocarbons

Intermediate products of radical reactions of chlorohydrocarbons catalyzed by copper chloride complexes were synthesized by the photolysis of solutions of [(C₄H₉)₃BzN⁺]₂[CuCl₄]^2? in chlorobenzene and chloroform at the wavelength corresponding to Cl → Cu charge transfer. It was shown by the EPR method that the products of photolysis were alkyl radicals formed by organic fragments of the quaternary ammonium cation and Cu(II) complexes (supposedly organocopper compounds). The total content of paramagnetic centers decreased. The mechanisms of photoreduction of quaternary ammonium tetrachlorocuprates and possible reasons for the decay of paramagnetic particles were considered.