Frequency-domain measurement of the photodegradation process of fluorescein

The frequency-domain technique is applied to measure the photodegradation rate of fluorescein in aqueous solutions. The illuminating light is modulated, and the changes in fluorescence from the illuminated region are detected synchronously. A constant flow rate is imposed on the fluorescein solution to control the mass transport of fluorescein into the illuminated region. The fluorescence response is described by a model that assumes that photodegradation occurs from the triplet excited state. The predictions of the model are consistent with the observed variations in the fluorescence response with flow rate, modulation frequency and incident power. We discuss in this article how the dependence of the model parameters on experimental conditions can be used to infer the photodegradation rate as well as some of the details of the photodegradation mechanism. The results are consistent with the known mechanism of photodegradation of fluorescein. The frequency-domain technique gives a photodegradation rate of 53 s(-1) in an air-saturated solution and 37 s(-1) in solutions purged with argon gas.     

On the extended method of calculation of atomic structures

The extended method of calculation of atomic structures is characterized. This method is understood as the use of as many radial orbitals as there are electrons in the atom under consideration. The process of passing from the ordinary method of calculation to the extended one is described. In the method proposed the additional complications appear within the confines of dealing with radial variables only. The general rules for carrying out the calculations, in applying the extended method, are formulated.     

A method for the assay of hydrolytic enzymes using dynamic light scattering

Dynamic light-scattering techniques have been successfully used for the assay of several hydrolytic enzymes. The enzymes were assayed using substrate-coated colloidal particles. Hydrolysis of the substrate coat causes destabilization of the particles followed by particle aggregation. The rate of particle aggregation can be related to the initial concentration of added enzyme.     

Additional symmetry for the electronic shell in its ground state and many-electron effects

The additional symmetry for the properties related to the ground state of the atom is considered taking into account many-electron effects. Calculations of the I _4f, I _3d,I _2p,I _3p binding energies, 4f ^N-15d - 4f^N system differences and 2p, 3p electron affinities in the second order of perturbation theory and in the configuration interaction approximation have been performed for the ground configurations with one open shell. The analysis of separate many-electron corrections for these quantities and their variation along the sequences of atoms and ions shows that the main corrections maintain the considered symmetry. Received 18 January 1999 and Received in final form 17 July 1999     

Hyperfine induced {\sf 1 s}{\sf 2 s}\ ^{\sf 1}S_{\sf 0} \rightarrow {\sf 1 s}^{\sf 2}\ ^{\sf 1}S0 M1 transition of He-like ions

Hyperfine induced $1s2s\ ^1$ S $_0 \rightarrow 1s^2\ ^1$ S₀ M1 transition probabilities of He-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. Present results for ¹⁵¹Eu and ¹⁵⁵Gd are in good agreement with previous calculations [L.N. Labzowsky et al., Phys. Rev. A 63, 054105 (2001)]. Electronic data are given in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine induced decay rates to be estimated for any isotope. The results should be helpful for future experimental investigations on QED and parity non-conservation effects.     

Raman and FTIR spectroscopies of fluorescein in solutions

Raman and Fourier transform-infra red (FT-IR) spectroscopies of fluorescein in aqueous solutions have been investigated in the pH range from 9.1 to 5.4. At pH 9.1 fluorescein is in the dianion form. At pH 5.4, fluorescein is a mixture of monoanion (approximately 85%), dianion and neutral forms (together approximately 15%). The fluorescence quantum yield drops from 0.93 for the dianion form to 0.37 for the monoanion form. The Raman and FT-IR studies focused on the frequency range from 1000 to 1800 cm(-1) which contains the skeletal vibrational modes of the xanthene moiety of fluorescein. At pH 9.1, the spectroscopic feature of fluorescein dianion are consistent with a picture of an electron delocalized among the xanthene moiety and two identical oxygens attached to opposite ends of the xanthene moiety, forming a very symmetric structure. The characteristic of fluorescein dianion is the presence of the phenoxide-like stretch at 1310 cm(-1). At pH 5.4, fluorescein monoanion has lost the symmetric structure characteristic of the dianion. The spectra of the monoanion have distinctive contributions from the phenolic bend at 1184 cm(-1). The assignments of the vibrational bands shown in Raman and FT-IR spectra are given based on both literature and the ab initio calculations at the Hartree-Fock level with HF/6-31 + +G* basis set. Excellent correlation is found between the experimental and calculated spectra.     

Density Functional Calculation of the Photoelectron Emission Spectra of BiSCl Crystal and Molecular Clusters

The photoelectron emission spectra of BiSCl crystal and molecular clusters have been calculated by the Density Functional Theory (DFT) method. Molecular clusters consists from 2 to 20 molecules in one double chain along z(c) axis. Total and partial density of states of BiSCl crystal and clusters have been weighted with atomic photoemission emission cross-section. The molecular clusters have been investigated including all normal modes of vibration. Theoretical results of BiSCl crystal and molecular clusters have been compared with experimental X-ray photoelectron emission spectra (XPS) of BiSI crystal.     

Hyperfine structure operator in the tensorial form of second quantization

The general tensorial form of the hyperfine interaction operator in the formalism of second quantization is presented. Both diagonal and off-diagnonal matrix elements of the above-mentioned operator are found using an approach based on a combination of second quantization in the coupled tensorial form, angular momentum theory in three spaces (orbital, spin and quasispin) and a generalised graphical technique. This methodology allows us to account for correlation effects efficiently and, therefore, to study the hyperfine interactions in complex many-electron atoms, those with openf-shells included, in a practical manner. All this will lead us to design an efficient program for large scale calculations of hyperfine structure and isotope shift.