Experimental method to measure the effect of charge on bimolecular collision rates in electrolyte solutions

A stable, monoprotic nitroxide spin probe is utilized as a model to study molecular collisions in aqueous electrolyte solutions. The rate constants of bimolecular collisions, K(col) for 2,2,5,5-tetramethylpyrrolidin-1-oxyl-3-carboxylic acid (CP) when it is uncharged (at low pH) and K(col)? when it is charged (CP?; at high pH), are measured as functions of temperature and ionic strength. The ratio f* ≡ K(col)?/K(col) is a direct measure of the effect of charge on the collision rate. Neglecting the small differences in size and diffusion coefficients of CP and CP?, f* is the fractional change in collision rate due to Coulomb repulsion which was treated theoretically in Debye's classic paper [Trans. Electr. Chem. Soc. 1942, 82, 265]. K(col) and K(col)? are determined from EPR spectral changes due to spin-spin interactions which are dominated by Heisenberg spin exchange under the conditions of these experiments. Values of f* vary linearly with values of κ · d in the range 0.4 < κ · d < 1.8, where κ and d are the inverse Debye screening length and the distance at closest approach, respectively. Values of d obtained in two independent ways, (1) from rotational correlation times measured by EPR and (2) by insisting that the experimental results be consistent with the Debye theory at infinite dilution, yield similar results. As the ionic strength is increased (κ increased), the screening effect reduces the effect of the Coulomb barrier more slowly than predicted by the Debye theory. While values of K(col) and K(col)? vary substantially with T, approximately following the Stokes-Einstein-Smoluchowski equation, values of f* depend only slightly on temperature at a given value of κ · d, as is predicted by Debye's theory.     

Anharmonic effects on theoretical IR line shapes of H-bonds

In the spirit of Y. Maréchal and A. Witkowski's [J. Chem. Phys. 48 (1968) 2697] work, one revisits, for weak H-bonds, the dependence of the angular frequency ω and of the equilibrium position q_e of the υ_X–H high frequency mode q, on the position coordinate Q of the low frequency υ_X–HY mode. One considers: ω=ω^o+bQ+cQ² and q_e=gQ+fQ². That leads to the anharmonic potential U: U=k₁q²+∑k_rQ^r+∑∑k_nmqⁿQ^m+k₁₅qQ⁵. Here k_r and k_mn (r=2–5, n=1,2 and m=1–4) are interrelated through b, c, g and f. By aid of the Hamiltonian involving U, we find the direct damped auto correlation function of υ_X–H, which, by Fourier transform, gives the IR spectral density (SD). When only b≠0, the SD is nothing but that given in a previous paper [P. Blaise, O. Henri-Rousseau, Chem. Phys. 243 (1999) 229]. When the adiabatic approximation is performed, this SD becomes that of N. Rösch and M. Ratner [J. Chem. Phys. 61 (1974) 3444] which reduces in turn to that of Maréchal and Witkowski in the absence of damping. With respect to b≠0, c produces a narrowing of the SD if c>0 and a subtle broadening if c<0. Besides, g induces the same narrowing for g>0 and g<0, while f gives subtle changes very sensitive to the sign of f and to the values of b, c and g. The situation b<0 and f>0 which is physically the most probable, leads to SDs which are the most evoking experimental profiles.     

Vibronic line shapes of PTCDA oligomers in helium nanodroplets

Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra.     

Vapochromic polyketone films based on aggregation‐induced enhanced emission

Aliphatic polyketone (PK) films physically mixed with moderate amounts (0.6 wt%) of 4,4′‐bis(2‐benzoxazolyl)stilbene (BBS) fluorophores were demonstrated to be sensitive to volatile organic compounds. Notably, BBS/PK blends were prepared by means of a continuous 1‐step extrusion process in a pilot‐scale twin screw extruder and compression molded followed by rapid quenching in liquid nitrogen to get thin films (thickness of 150 μm) containing molecularly dispersed blue emissive BBS fluorophores. The 0.6 wt% BBS/PK films demonstrated significant vapochromism when exposed to volatile organic compounds characterized by favorable interactions with the polymer matrix such as chloroform. Solvent absorption caused PK matrix plasticization, thus increasing BBS mobility and triggering the self‐associations of molecules into bluish green‐emissive excimers/aggregates thanks to the emersion of the typical band at 500 nm. This phenomenon preferentially involves the BBS/PK film layers close to the air‐contact surface without affecting the bulk characteristics of the PK matrix. The easy modulation of the luminescent properties of PK films by varying the supramolecular organization of BBS dispersed molecules by chemical perturbations, and the use of melt‐processing procedures suggests the use for the first time of aliphatic PK in the development of smart materials for sensing applications.     

Selection of an analytical line for determining lithium in aluminum alloys by laser induced breakdown spectrometry

Possibilities for determining lithium in aluminum alloys by laser spark spectrometry are studied. The optimum conditions for registering the emission signal of lithium at which the effect of the continuous background radiation of the laser plasma attains a minimum are found. The possibility of determining lithium by laser spark spectrometry using the spectral line at 610 nm is studied for the first time. A comparison of the detection limits and sensitivities of determining lithium by emission its lines at 610 and 671 nm has indicated the advisability of using the line 610 nm for the studied alloys. The detection limit calculated using the 3σ test was found to be 230 ppm (610 nm) and 870 ppm (671 nm).     

Classical light scattering studies on structure formation in polymer solutions

The scattered light is very sensitive to the presence of supermolecular structures in polymer solutions, offering the possibility to study structure formation in situ by classical light scattering and to characterize the generated particles. An improved analysis of light scattering data yields information on the structure type, polydispersity of the systems, particle mass and size as well as the degree of swelling. The flocculation process of ampholytic modified poly(acrylonitrile) was investigated in dependence on the pH-value and the content of different salts in the solvent. Results obtained give a deeper insight into the flocculation mechanism.     

A study of diffractometer line shapes in melt crystallized polyethylene

Wide angle X-ray diffraction scans of isothermally crystallized samples of polyethylene containing known levels of chain defects have been investigated. An analysis of scattering curves using a powder diffractometer is reported. The analytical deconvolution of Lorentz and Lorentz squared profiles for the PE experimental scattering curve and the standard is performed to give the pure profile for the polymer. The separate contribution of paracrystalline lattice distortions and coherently diffracting domains, in different crystallographic directions, to the broadening of the diffraction profiles is discussed in the light of the level of defects present.     

Hamiltonian theory for vibrational line shapes of atoms adsorbed on surfaces

The vibrational motions of atomic adsorbates on surfaces can be probed by helium atom scattering. The experimental observable is the dynamic structure factor, which shows an inelastic peak around the vibrational frequency of the isolated adsorbates known as the frustrated translational or T-mode peak. In this paper we develop a theory for the line shape of this peak, as well as for its temperature-dependent shift and broadening, based on a Hamiltonian equivalent of the generalized Langevin equation. The theory can be used to infer physical parameters of the adatom-surface interaction, such as the friction coefficient, the barrier height to diffusion, and the anharmonicity parameter. Numerical simulations are used to ascertain the range of validity of the theory, which is also generalized to describe multidimensional systems and to include quantum corrections. We compare the theoretical predictions for the shift and broadening with experimental results for the Na/Cu(001) system, showing quantitative agreement within experimental resolution.     

Spot test for sulfites based on the induced oxidation of cobalt-azide solutions

Summary The autoxidation of solutions containing cobaltous and excess azide ions is considerably accelerated by minute amounts of sulfites. Experimental evidence supports the view that the autoxidation of sulfurous acid induces the oxidation of cobalt from the divalent to the tervalent state. A spot test for the detection of sulfites has been developed on the basis of this phenomenon. The test is performed on filter paper. Limit of identification: 0.5g NaHSO₃. Dilution limit: 1100000. Large amounts of thiosulfate ions inhibit the test but can be easily removed.

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Zusammenfassung Die Autoxydation von Kobalt(II)-lösungen, die überschüssige Azidionen enthalten, wird durch kleine Mengen Sulfit erheblich beschleunigt. Versuche deuten darauf hin, daß die Autoxydation der schwefeligen Säure die Oxydation des Co(II) zu Co(III) induziert. Auf dieser Grundlage wurde ein Tüpfelnachweis für Sulfit ausgearbeitet. Er wird auf Filterpapier ausgeführt. Erfassungsgrenze: 0,5g NaHSO₃; Grenzkonzentration: 1100000. Große Mengen Thiosulfat stören den Nachweis, können aber leicht entfernt werden.

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Résumé L'autoxydation de solutions contenant des ions cobalteux et des ions azotures en excès est considérablement accélérée par des quantités de sulfites extrêmement faibles. L'hypothèse de l'induction de l'oxydation du cobalt de l'état divalent à l'état trivalent par l'autoxydation de l'acide sulfureux est confirmée par l'expérience. On a mis au point un essai à la touche pour la détection des sulfites sur la base de ce phénomène. L'essai est effectué sur papier filtre. Limite d'identification: 0,5g NaHSO₃. Limite de dilution: 1100000. La réaction est inhibée par la présence d'ions thiosulfates en quantités importantes, mais ces ions sont faciles à éliminer.

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Part of a communication presented at the XVth International Congress for Pure and Applied Chemistry, Lisbon, September 1956.     

Test determination of aniline in solutions based on azo coupling with analytical reagents incorporated into silicic acid xerogels

Silicic acid xerogels modified with 1-naphthol, 2-naphthol, 8-hydroxyquinoline, 2,7-dihydroxynaphthalene,N-(l-napthyl)ethylenediamine andp-hydroxydiphenyl were synthesized. It was shown that the immobilized reagents can participate in reactions of azo coupling with products of aniline diazotization. The best (among the studied) immobilized reagent for determining aniline was 1-naphthol. Xerogel modified with 1-naphthol was used for determining aniline in solutions by solid-phase spectrophotometry and with visual detection. The analytical ranges for aniline at the optimal conditions were 0.005-10 mg/L using solid-phase spectrophotometry and 0.05-15 ng/L with visual detection. The results were verified in the analysis of synthetic mixtures.     

A qualitative analysis of individual trajectories in the rotationally inelastic LiHHe collision system

Individual trajectories corresponding to classical mechanical collisions between He and LiH (rigid rotor) are examined to identify characteristics of the rotational transfer process. Torque is found to be useful for understanding rotational transitions and for defining an interaction time.     

Asymmetric Stark broadening of the Fe I 538.34 nm emission line in a laser induced plasma

In this work asymmetries along with shifts in the line profiles of neutral iron emission lines coming from a laser induced plasma have been detected. The plasma was produced in air at atmospheric pressure on a 50% Fe–Ni alloy and the emission was collected at a temporal window of (2.5, 3) μs. To avoid the effect of spatial inhomogeneity on the profiles, a deconvolution procedure was applied to obtain the spatially resolved emissivity. Asymmetric theoretical Stark profiles, which take into account the effect of static ions, were used to be fitted to the experimental data of the emission profile of the line Fe I 538.34 nm. The fitting of the theoretical profile to the experimental data was carried out by means of the least squares method using genetic algorithms to automatically solve the optimization problem. The correlation coefficient was higher for the asymmetric fits than for the symmetric ones. From the fit, the quasistatic ion broadening parameter α, the electron broadening parameter w_e, and the total shift of the maximum of the line d_t, were obtained. The ion parameter α varied in a range (0.2–0.3) for an electron density between (4–15) × 10¹⁶ cm^− 3. The ion influence on the total broadening was of 15–20%. The total shift varied in the range (0.01–0.06) nm and it was mainly given by the ion shift, the electron shift being negligible. For the electron density range in this work, approximated linear behaviors of the total width and shift with electron density have been obtained.     

A fluorescence emission study of the formation of induced premicelles in solutions of polyelectrolytes and ionic surfactants

The interactions between PSS-co-BVE copolymers and ionic surfactants (anionic and cationic) in aqueous solution have been investigated using pyrene as a photophysical probe. Static and dynamic fluorescence determinations have been used to obtain information about the microenvironments formed between both species. Micropolarity studies using the I1/I3 ratio of the vibronic bands of pyrene and the behavior of the I(E)/I(M) ratio between the monomer and excimer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and the oppositely charged surfactants lead to the formation of induced premicelles at surfactant concentrations lower than the cmc of the surfactants. This aggregation process is assumed to be due to electrostatic attraction. At the same concentration, the excimer-to-monomer emission ratio shows its first peak. At higher surfactant concentrations, near the cmc, micelles with the same properties as those found in pure aqueous solution are formed. On the other side, systems containing an anionic surfactant do not show this behavior at low concentrations. There is no apparent dependence of the cac on the composition of the polymer, reinforcing the assumption that the electrostatic interactions induce the formation of the premicelles. The values of the cac's follow the same trend as for the cmc's, DTAC>DTAB>CTAC. The polarity of the induced premicelles, as measured by the I1/I3 ratio, also indicates that the microdomains formed by the longer chain surfactants are more hydrophobic than those of the shorter chain surfactants, as also happens with real micelles.     

Energetic potential of solid composite propellants based on CL-20-containing bimolecular crystals

The energetic potential of bimolecular crystals (BMCs) containing CL-20 as components of solid composite propellants (SCPs) was investigated. The experimental and calculated values of the standard enthalpies of formation are reported. The maximum heats of explosion, which correlate with the impact sensitivity, were calculated. The specific impulse values and the densities of SCPs based on an active binder, aluminum, and oxidizer (BMC + a small portion of ammonium dinitramide) were evaluated.     

Revelation of bimolecular tautomerization induced by the concerted and radical interactions in lignin pyrolysis

Bimolecular interactions play crucial roles in lignin pyrolysis.The tautomerization of key intermediates has a significant impact on the formation of stable products,whereas bimolecular tautomerization has been rarely clarified.In the present work,the bimolecular tautomerization mechanism induced by both concerted and radical interactions was proposed and carefully confirmed.A characteristic β-O-4 lignin dimer,2-phenoxy-1-phenylethanol(α-OH-PPE),was used as the model compound to reveal two repre...     

Collisional line shapes for low frequency vibrations of adsorbates on a metal surface

The dynamics of atoms or molecules adsorbed on a metal surface, and excited by collisions with an atomic beam, are treated within a theory that includes energy dissipation into lattice vibrations by means of a frequency and temperature dependent friction function. The theory provides dynamic structure factors for energy transfer derived from collisional time correlation functions. It describes the relaxation of a vibrationally excited atom or molecule within a model of a damped quantum harmonic oscillator bilinearly coupled to a bath of lattice oscillators. The collisional time correlation function is generalized to include friction effects and is applied to the vibrational relaxation of the frustrated translation mode of Na adsorbed on a Cu(001) surface, CO on Cu(001), and CO on Pt(111), following excitation by collisions with He atoms. Results for the frequency shift and width of line shapes versus surface temperature are in very good agreement with experimental measurements of inelastic He atom scattering. Our interpretation of the experimental results provides insight on the relative role of phonon versus electron-hole relaxation.     

Doppler-broadened line shapes of atomic hydrogen in a parallel-plate radio frequency discharge

Doppler-shifted atomic hydrogen emission (Balmer ) is observed from a low-frequency rf discharge through molecular hydrogen by collecting the light through a hole in one of the electrodes. Doppler shifts as large as 0.7 nm, corresponding to an energy of 540 eV or 85% of the peak applied voltage, are observed when ions are accelerated by the sheath electric field. The mechanisms for hot atom production are discussed in terms of both gas-phase and surface ion-impact phenomena. Hot atoms are produced via gas-phase ion-atom and ion-molecule collisions, as a result of simultaneous neutralization and reflection of ions at the electrode surface, and/or by sputtering of adsorbed hydrogen. As much as 30% of the atomic hydrogen emission is substantially Doppler shifted, indicating that most of the atomic emission in the sheaths is actually produced by ion impact and not by electron impact.