Molecular photofragment orientation in the photodissociation of H2O2 at 193 nm and 248 nm

Angular momentum orientation has been observed in the OH(X(2)Π, v = 0) fragments generated by circularly polarized photodissociation of H(2)O(2) at 193 nm and 248 nm. The magnitude and sign of the orientation are strongly dependent on the OH(X) photofragment rotational state. In addition to conventional laser induced fluorescence methods, Zeeman quantum beat spectroscopy has also been used as a complementary tool to probe the angular momentum orientation parameters. The measured orientation at 193 nm is attributed solely to photodissociation via the ?(1)A state, even though at this wavelength H(2)O(2) is excited near equally to both the ?(1)A and B(1)B electronic states. This observation is confirmed by measurements of the photofragment orientation at 248 nm, where access to the ?(1)A state dominates. Several possible mechanisms are discussed to explain the observed photofragment orientation, and a simple physical model is developed, which includes the effects of the polarization of the parent molecular rotation upon absorption of circularly polarized light. Good agreement between the experimental and simulation results is obtained, lending support to the validity of the model. It is proposed that photofragment orientation arises mainly from the coupling of the parent rotational angular momentum with that induced during photofragmentation.     

In situ activation analysis of marine sediments with252Cf

A seabed nuclear probe has been developed which permits the measurement of up to 33 elements at the parts per thousand to parts per million levels in continental shelf areas. The probe consists of a neutron irradiation source,²⁵²Cf, which neutron activates the elements in the minerals of interest. These resulting radioactive elements emit characteristic gamma radiation which is analyzed in situ in 2- to 10 min counting intervals with a Ge(Li) detector system. Details of the irradiation source, the Ge(Li) detector, and spectra taken in situ in a marine environment are discussed with respect to the detection of the minerals at concentrations of economic interest.     

MR of an adrenal pseudocyst

We describe the appearance of an adrenal pseudocyst on MRI and CT. The MR characteristics of the lesion were noteworthy in that the lesion had two components with different imaging characteristics. The larger component was of low signal intensity on both T₁- and T₂-weighted images and might have been confused with an adrenal adenoma.     

Quasi-particle excitations and phonon broadening effects in the O ls spectra of Ln(OH)3 (Ln = La,Nd, Sm and Gd)

The O ls photoelectron spectra of Ln(OH)₃ (Ln = La, Nd, Sm and Gd) can be approximated by the convolution of a core hole spectral density function and a response function which is related to the phonon broadening and instrumental broadening effects. A non-linear least-squares analysis on the convolution integral indicates that the lifetime of the O ls (in the energy domain) is strongly broadened by the phonon excitations. The FWHM (full width at half maximum) of the phonon excitations range from 1.3 to 2.6 eV.     

The electronic state of butadiene bonded to an iron tricarbonyl residue

A theoretical study of tricarbonylbutadieneiron by the all valence electron SCFMO method is presented.The charge distribution on the butadiene group in the complex appears to correspond to a mixture of excited electronic states of the free molecule and this is found to be consistent both with the experimental geometry of the molecule and its reactions. The charge distribution shows that the iron atom assumes a negative charge in the complex and that this arises from the carbonyl carbon atoms. The bonding pattern of the molecule involves mainly the electronic levels of butadiene, although the set are also somewhat perturbed When the Fe-diene distance is increased, the excited electronic states are retained in the organic moiety.We thank the S.R.C. and the Scottish Education Committee for Maintenance Grants (to I.C.R. and J.M.S.).     

An anticoincidence-shielded Ge(Li) gamma-ray spectrometer and its application to radioanalytical chemistry problems

An anticoincidence-shielded Ge(Li) γ-ray spectrometer incorporating a largevolume, high-resolution coaxial diode inside a large plastic phosphor shield is described. It provides a peak-to-Compton ratio of 245: 1 for¹³⁷Cs and a significantly improved sensitivity for both low- and high-level radionuclide measurements. Examples of its application to neutron activation analysis, analysis of proton activated sources, and environmental radionuclide analysis are illustrated. This paper is based on work performed under United States Atomic Energy Commission Contract AT(45-1)—1830.     

Calculations on some phosphate ions by a modified CNDO method

Calculations are presented of the electronic structures of some phosphate ions, namely, H₃PO₄, H₂PO ₄ ^– , HPO ₄ ⁼ , PO ₄ , HPO₃, and PO ₃ ^– . It is shown that the character of the P-O bonds is marked and the 3d orbitals contribute substantially to the bonding. Using the total energy data for the orthophosphate ions, the ratio of the dissociation constants for the ions is calculated and found to be in good agreement with the experimental data.     

Vibrational spectroscopic studies of (3-mercaptopropyl)trimethoxylsilane sol-gel and its coating

Organosilane sol-gels have been prepared under different conditions from mercaptopropyltrimethoxysilane (MPTMS) and mercaptopropyltriethoxysilane (MPTES). These sol-gels were applied for the thin film coating on aluminum. Vibrational spectroscopy has been employed to trace and to study the proceeding of the sol-gel formation and the curing of the coated films on Al. Based on the group frequencies as well as their spectral behavior under different conditions, vibrational assignments have been made for most of the observed bands. Surface enhanced Raman scattering has revealed the chemical adsorption of MPTMS sol-gel on silver particles. Recorded reflection and absorption infrared (RAIR) spectra of coated tiles cured at different temperatures have indicated that surface reaction may occur at high temperature. The anticorrosion characters of the coated metals have been evaluated with the measured electrochemical data. Results from cyclic voltammographs have indicated that each layer of sol-gel coating would reduce the redox current across the electrode/electrolyte solution interface. Tafel plots have shown that the anodic current of the coated electrode decreases significantly and the corrosion potentials shift to the positive side.