David M. Hercules

An ESCA study of organosilicon compounds

Abstract The silicon 2p electron binding energies have been measured for a series of 33 organosilicon compounds. The binding energies are correlated with partial atomic charges calculated by various electronegativity models and CNDO calculations. Group shifts are reported for various chemical groups attached to silicon and are found to correlate with group shifts reported for carbon and phosphorus compounds.

A Chemiluminescence Detector for Transition Metals Separated by Ion Exchange

Abstract The means by which transition metals, separated as anionic complexes by ion exchange column, can be detected is described. The chemiluminescence of the luminol-H2O2 reaction catalyzed by these metals as they emerge from the column and are monitored continuously is used as the detector. Other studies have shown that the emission is proportional to the catalyst concentration; this fact is relied upon in this study.1–9

STUDIES ON SOME INTERMEDIATES AND PRODUCTS OF THE PHOTOREDUCTION OF 9,10‐ANTHRAQUINONE *,†

Abstract— The mechanism of the photoreduction of 9,10‐anthraquinone (AQ) in alcohol and hexane has been studied by flash photolysis. The fluorescence spectrum of the photoproduct, 9,10‐dihydroxy anthracene shows a large shift between hexane and ethanol. The quantum yields of photoreduction for AQ are solvent‐dependent, the reaction between the solvent radical and AQ determining the quantum yield.

Enzyme-Induced Chemiluminescence-Determination of Blood Glucose Using Luminol

Abstract Hydrogen peroxide, produced by the interaction of glucose with immobilized glucose oxidase, reacts with the ferricyanide-luminol system to produce chemiluminescence linearly proportional to glucose concentration. The coupled reaction is used as a sensitive precise micro method for the determination of true blood glucose. The linear range of detection is 10−7 - 10−4 M glucose. The method correlates quantitatively with two glucose reference techniques.

Devaluation of the gold standard in x-ray photoelectron spectroscopy

Abstract The value of vapor-deposited gold as a standard in x-ray photo-electron spectroscopy has been studied. During the deposition gold may react with the sample giving consequent shifts and/or broadening of the Au 4f peaks. Shifts to higher binding energies have been observed with KCN and NACl and to lower energies with Na 2 S 2 O 3 and copper phthalocyanine. The An 4f peaks have been investigated over the temperature range −50 to 200°C. At higher temperatures peaks due to metallic gold are observed. Anomalous effects have been observed in the XPS spectrum of gold plated copper phthalocyanine in the binding energy range 650–950 eV.

Composition of Fluoridated Dental Enamel Studied by X-ray Photoelectron Spectroscopy (ESCA)

Enamel surfaces that had been treated with an acid phosphate-fluoride gel were analyzed for phosphorus, calcium, fluorine, and carbon using X-ray photoelectron spectroscopy. This technique revealed a heavy carbon coating on the enamel that overlays a surface composed of a 1:2 ratio of calcium to fluorine. Evidence is presented for a noncaL cium phosphorus species in the surface layer. Removal of successive layers of enamel by argon-ion etching showed a steady decrease in fluorine and a corresponding increase in phosphorus concentrations.

Application of X-ray Photoelectron Spectroscopy to the Study of Fiberglass Surfaces:

The application of x-ray photoelectron spectroscopy (ESCA) to the study of fiberglass surfaces is reported. Qualitatively, ESCA has been used to show the change in concentration of elements at the surface when fiberglass is subjected to heat and/or acid treatment. Diffusion of calcium to the surface as a function of temperature has been studied. Similarly, leaching of aluminum by acid as a function of pH is reported. The ability of ESCA to detect organic functional groups attached to fiberglass surfaces has been demonstrated for nitrogen and sulfur. Fiberglass coated with organic groups having chelating properties has been shown to extract metals from solution. It has also been demonstrated that ESCA can follow reactions of organic functional groups on glass surfaces, namely sulfonation of an amine.

Analytical studies using iodine—luminol chemiluminescence

Trace amounts of substances have been related to iodine consumption monitored by chemiluminescence from the iodine-luminol system. Iodine titrations of sulphite and arsenic(III) have been carried out at levels of 1.0 x 10(-7) and 5.0 x 10(-8)M with a precision and error of better than 1% on a day-to-day basis. A calibrated standard of 1.8 ppm SO(2) in air was analysed with a precision of +/-1.2%, and an error of 0.9%. A rate method has been developed based on the reaction between iodine and penicillin G; a linear range from 10(-8) to 10(-7)M was found, the precision being +/-9%.

Correlations between ESCA chemical shifts and modified sanderson electronegativity calculations

Abstract Correlations are given between ESCA chemical shifts and partial atomic changes calculated by the modified Sanderson method. Elements included are boron, carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, oxygen, sulfur, selenium, fluorine, chlorine and bromine. Successful correlations were obtained for most elements; the best success was for situations involving a constant number of σ bonds. The method was least successful for nitrogen, oxygen, chlorine and bromine. The modified Sanderson method performed comparably to CNDO and Jolly electronegativity calculations in most cases. Correction for molecular potential is automatically achieved using the modified Sanderson method. When the data for all elements are considered the MS model seems to work reasonably well. Correlations for B, C, Ge, F, N, As and Se seem to be as good as most methods applied to these elements. The MS method works particularly well for Si, Sn, P and S. It is inapplicable to O, Cl and Br. For compounds of elements which exist in more than one formal oxidation state, it is necessary to obtain a separate plot of E B , versus q i for each oxidation state. Once this is done, the calculated and experimental binding energies show good correlation. The slopes and intercepts given in Table 3 may be used for this purpose. The reason for separate correlation lines in the case of multiple oxidation states may be understood when one considers the method by which Sanderson originally calculated his atomic E values. Sandersons original E values were calculated as the ratio of the electron density of an element stripped of all its valence electrons to the electron density of the corresponding inert gas. By considering only the inert shell configuration, Sandersons E values are valid for filled electron shell oxidation states. However, no allowance for lone electron pairs is made. Thus, charges calculated by Sandersons method for elements bound in less than their maximum oxidation state may not be correct relative to other oxidation states of the same element. Attempts to correct for this neglect of lone pairs were made during the course of this work by assigning E values for an electron pair or by calculating E values for non-inert shell valence configurations met with failure. The low slopes of the binding energy-charge correlations for oxygen and the halogens may also be explained by the method Sanderson used to calculate his atomic E values. Sanderson assumed that all elements shared all valence electrons in bonding. This is not the case for the halogens or oxygen which retain essentially inert lone electron pairs. Since the effect of these lone pairs is not specifically dealt with, the charges calculated by Sandersons method and the MS method are larger than they should be in the case of elements which retain nonbonded lone pairs.Throughout these studies, it has been noted that the MS method needs no correction for molecular potential. This may be explained by the manner in which group E values are calculated. Since the electronegativities of the atoms comprising a group are “sequentially” equalized from the terminal atom of a group inward to the site of the central atom, through bond inductive effects are accounted for. This procedure reduces a multiatom group to a form in which it may be treated as a single atom attached to the atom of interest. In this form, a molecule is reduced to Paulings “nearest neighbor” picture. Thomas 19 has found that Paulings “nearest neighbor” approximation works well for correlating ESCA data of small (e.g. methane-line) molecules without additional correction for molecular potential. Thus, the MS method has reduced a molecule to a form where the “nearest neighbor” approximation is applicable. The MS method works well for covalent molecules. As was pointed out earlier, the method fails for ionic solids primarily because of anomalies introduced by the Madelung potential. It is speculated that the MS method will work well for isolated ionic molecules in the gas-phase.

A study of some potassium hexachlorometallate complexes using electron spectroscopy

Abstract X-ray photoelectron (ESCA) spectra of the core (Cl 2 p K 2 p and metal 4 f , if present) and valence orbitals are reported for K 2 ReCl 6 , K 2 OsCl 6 , K 2 IrCl 6 · 3 H 2 O, K 2 PtCl 6 , K 3 MoCl 6 , and K 2 SnCl 6 . The K 2 p 3 2 binding energy was found to be nearly constant (292.7 eV) and that of Cl to increase very slightly with increasing atomic number for the third row transition metals. The chemical shifts of Re(IV), Os(IV), Ir(IV), and Pt(IV) relative to the metals were in qualitative agreement with atomic calculations utilizing configurations obtained from extended Huckel calculations. The valence spectra of the transition metal complexes exhibit a three-band structure. On the basis of MO results and intensity considerations the high binding energy band is assigned as a composite of the a 1g , e g , 1 t 2g MOs. The middle band represents the t 2u , 2 t 1g MOs; and the low binding energy band the 2 t 2g MO. Calculated nd orbital photoionization cross sections correlate reasonably well with the relative intensifies of the valence manifolds. Comparison of band separations and charge-transfer transition energies suggests that interelectronic repulsion and MO energy separation contribute about equally to the overall charge-transfer energy.