Short Time Domain Research Articles

Reversible oxidation processes in dichloromethane for triethyl-, diethyl-, trimethyl-, and dimethyllead compounds at mercury electrodes

Chemically reversible electrochemical oxidation processes have been observed at mercury electrodes in dichloromethane in the presence of Et 3PbOAc (OAc − = acetate), Et 3PbCl, Et 2PbCl 2, Me 3PbOAc, Me 3PbCl and Me 2PbCl 2. The trialkyl derivatives R 3PbX (R  Et, Me; X −  OAc −, Cl −) give rise to a reversible oxidation process involving transfer of one electron, exchange of alkyl groups and X − and formation of a mercury-lead complex, which in its simplest form can be represented as [R 3PbHgPbR 3] 2+. The oxidation process is therefore described by the equation 2 R 3PbX + 2 Hg ⇌ [R 3PbHgPbR 3] 2+ + HgX 2 + 2 e − On the longer time scale of controlled potential electrolysis, HgX 2 can react with R 3PbX and presumably [R 3PbHgR 3Pb] 2+ to produce RHgX, inorganic lead(II) and electroactive R 2PbX 2. The dialkyl complexes R 2PbX 2 exhibit analogous oxidation processes of the kind 2 R 2PbX 2 + 2 Hg ⇌ [R 2XPbHgPbXR 2] 2+ + HgX 2 + 2 e − with short time domain experiments. However HgX 2 reacts with [R 2XPbHgPbXR 2] 2+ and R 2PbX 2 on longer time domain experiments such as controlled potential electrolysis or dc polarography to generate inorganic lead(II) and RHgX. The existence of reversible polarographic processes implies that it may be possible to develop extremely sensitive analytical methods for the determination of these toxic and environmentally significant compounds based on procedures incorporating (i) extraction into non-polar solvents, (ii) high performance liquid chromatography and (iii) electrochemical oxidative detection without the need to remove oxygen as is required when using previously described reduction processes.

Spectroscopic Studies of Photochemical Reactions in Organic Solids. Photodimerization of p-Formylcinnamic Acid

Abstract Raman phonon spectroscopy and electronic absorption and emission spectroscopy have been used to study the mechanism of reaction and the role of electron–phonon coupling in determining the photoreactivity of p-formylcinnamic acid (p-FCA) in the crystalline state. Raman and infrared spectroscopy in the internal vibration region have been used to characterize the reactant p-FCA and the dimeric product t-3,t-4-bis(p-formylphenyl)-ν-1,c-2-cyclobutanedicarboxylic acid. Phonon spectroscopy reveals that the reaction proceeds principally by a heterogeneous mechanism though a homogeneous mechanism in the initial stage of short time domain can not be ruled out. The electronic spectroscopy suggests a strong electron–phonon coupling in the monomer crystal.

Collisional quenching of electronically excited chlorine atoms, Cl[3p 5(2 P 1/2)], by atmospheric gases studied by time-resolved atomic resonance absorption spectroscopy in the vacuum ultraviolet

The collisional quenching of electronically excited chlorine atoms, Cl[3p5(2P1/2)], has been studied by time-resolved atomic resonance absorption spectroscopy in the vacuum ultraviolet at λ= 136.34 nm {Cl[3p4 4s(2P3/2)]â†� Cl[3p5(2P01/2)]}. Cl(3 2P1/2) was generated by the repetitive pulsed irradiation of CCl4 in the presence of excess helium buffer gas. The excited atom was then monitored photoelectrically using signal averaging in the short-time domain before the onset of Boltzmann equilibrium. The following absolute second-order rate constants for the removal of Cl(3 2P1/2), 882 cm–1 above the 3 2P3/2 ground state, are reported (kQ/cm3 molecules–1 s–1, 300 K, errors 1 σ) for a wide range of gases of atmospheric interest: N2, (6.3 ± 1.0)× 10–13; CO2, <5 × 10–13; O2, (2.3 ± 0.3)× 10–11; N2O, (3.7 ± 0.6)× 10–13; H2, <6 × 10–13; H2O, (2.6 ± 0.5)× 10–12; HCl, (1.1 ± 0.1)× 10–12; CH4, (3.9 ± 0.8)× 10–12; CO, ca. 6 × 10–12. These rate data are compared with the collisional-quenching rate constants for the other gases that we have reported previously using this technique which is, at present, the only practical method for monitoring Cl(3 2P1/2) out of Boltzmann equilibrium for fundamental reasons discussed in this paper. General considerations of the chemistry of a Boltzmann system of Cl(3 2PJ) and the roles of the specific spin–orbit states, Cl(3 2P1/2) and Cl(3 2P3/2), are presented with special reference to CH4 and the atmospheric gases in general. Relative rate data for the quenching of the transient precursor, generated from the photolysis of CCl4 and from which Cl(3 2P1/2) is derived, are also presented for most of the gases studied.

Particle-induced desorption mass spectrometry of large involatile biomolecules: surface chemistry in the high-energy short-time domain

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTParticle-induced desorption mass spectrometry of large involatile biomolecules: surface chemistry in the high-energy short-time domainRonald D. MacfarlaneCite this: Acc. Chem. Res. 1982, 15, 9, 268–275Publication Date (Print):September 1, 1982Publication History Published online1 May 2002Published inissue 1 September 1982https://doi.org/10.1021/ar00081a001RIGHTS & PERMISSIONSArticle Views101Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Surface chemistry in ion-induced desorption

A new aspect of track formation in solids by high energy ions is the phenomenon of ion desorption from the surface of the track. Experimental evidence points to the notion that a thermal spike attaining a transient temperature of 10 4 K is formed. In this paper a suggestion is offered that the ions that form are the result of condensed phase surface chemistry in the high energy short-time domain. Some elementary considerations are offered on how the processes might be treated within the framework of classical chemical thermodynamics and kinetics.

Sum Rule and Hydrodynamic Analyses of the Velocity Autocorrelation Function in Strongly Coupled Plasmas

The memory function for the velocity autocorrelation function in a strongly coupled, one-component plasma is analyzed in the short time and long time domains, respectively, with the aid of the frequency-moment sum rules and the hydrodynamic consideration evoking the idea of the generalized Stokes friction. A series of interpolation schemes with successively improved accuracies are then introduced. Numerical investigations of those interpolation schemes clarify the physical origin of the three different types of the velocity autocorrelation function observed in the molecular dynamics simulation at different regimes of the coupling constant.

Molecular interactions in the benzene-hexafluorobenzene liquid system

The molecular dynamics of the liquid systems benzene, hexafluorobenzene and the benzene-hexafluorobenzene “complex” have been investigated using i.r. and Raman lineshapes. Time correlation functions computed by the Fourier inversion of the appropriate spectral band shapes were used to probe the molecular motion. In the short time domain 0–1.5 ps there seems to be no preferred orientation between benzene and hexafluorobenzene. The results are consistent with the presence of weak intermolecular interactions which exist only during the lifetime of a molecular collision. Vibrational relaxation was found to be significant for the lower frequency modes.