Mode specificity of unimolecular rate constants in the Hénon-Heiles system

The tunneling widths of high-energy metastable states lying in the classical irregular region of the Hénon-Heiles potential energy surface were calculated via complex analytical continuation of stabilization graphs. Mode specificity is demonstrated in that the lifetimes of normal-mode, local-bond-mode, and mode-mixed states at nearby energies differ by an order of magnitude.     

Mode interaction through amplitudes and phases in a two-modegyrotron oscillator

An analysis is made of temporal evolution of electromagnetic modes in a two-mode gyrotron oscillator characterized by phase and amplitude interaction through the terms linear in the oscillator power. The problem is solved in the context of amplitudes and phases which vary slowly compared with the period of oscillation. Specific reference is made to competition between TE_11q modes in a closed cavity gyrotron. Qualitative features which are found include phase locking, beat frequencies, periodic pulling, and mode excitation. This work has applicability when the frequency separation between the modes is on the order of the frequency bandwidth of each mode, or the modes are equally spaced in frequency. Gyrotrons of this type include those with low-quality-factor modes or degenerate modes. Phase interaction in the case of equally spaced cavity modes is of importance in analyzing mode-locking phenomena     

The preparation and utilization of performance evaluation soils for evaluating radioassay laboratories engaged in site remediation work

Site remediation projects dealing with uranium, thorium or radium require the services of a radioassay laboratory during the site characterization, remediation and final site survey/verification phases. In the U.S., regulatory agencies and industry guidelines recommend that the remediation contractor conduct an external laboratory QC program to ensure the quality of the analytical results. The commercial availability of certified natural soil matrices is extremely limited not only by nuclide and nuclide concentration but also by soil type. In most cases, the applicability of these materials for an external QC program is questionable since the chemical constituents of the certified soil may not be representative of the remediation soil type. Also, such materials are typically only suitable as single blind performance evaluation (PE) samples. The Yankee Atomic Environmental Laboratory (YAEL) has characterized soil materials from several uranium mining and milling sites for use in two laboratory PE programs. The site specific PE materials were prepared in accordance with their intended use and quality performance requirements. One PE material was dried, pulverized to a particle size of approximately 10 microns and homogeneously blended. The second PE material (total of 1,024 kg) was methodically field blended and aliquoted to produce 1,000 separate homogeneous 1 kg samples. Both PE materials were characterized for radionuclide concentration and heterogeneity or sample distribution. A summary of the characterization studies of the different PE materials as well as the quality performance criteria developed for evaluating the laboratory's performance and the advantages and disadvantages of using each PE material will be discussed and summarized.     

WILLGERODT-KINDLER'S MICROWAVE-ENHANCED SYNTHESIS OF THIOAMIDE DERIVATIVES

The Willgerodt-Kindlerreaction was applied to a series of aromatic aldehydes and ketones. The reactions were performed in a dipolar aprotic solvent (mainly DMF) in the presence of a base catalyst (4-methylmorpholine) and utilized microwave (mw) irradiation. The pulsed mw technique rather than the continuous irradiation was preferred because it limited side reactions and hydrogen sulfide production. While not always superior to the thermal activation of the reaction, the procedure involving repetitive short pulses of microwave irradiation was found to be faster and result in consistently cleaner products. The technique can be easily applied in a fast parallel synthesis process.     

Solution-phase parallel synthesis of spirohydantoins

Spirohydantoins are considered privileged structures, making them attractive for the preparation of compound libraries with the potential for diverse biological activity. However, very few modifications of this scaffold have been reported to date. The spirohydantoin template was elaborated into a library of 168 compounds through a two-step solution-phase parallel synthesis starting from various N-substituted piperidinones. The Strecker reaction was employed to generate alpha-amino nitriles from aniline and TMSCN (or KCN). Subsequent reaction of the anilido nitrogen with a diverse set of isocyanates, followed by refluxing under acidic conditions, afforded the title library in high yield and purity.     

A Photoprotective Effect by Cation-π-Interaction? Quenching of Singlet Oxygen by an Indole Cation-π Model System

We investigated the effect of the cation-π interaction on the susceptibility of a tryptophan model system toward interaction with singlet oxygen, that is, type II photooxidation. The model system consists of two indole units linked to a lariat crown ether to measure the total rate of removal of singlet oxygen by the indole units in the presence of sodium cations (i.e. indole units subject to a cation-π interaction) and in the absence of this interaction. We found that the cation-π interaction significantly decreases the total rate of removal of singlet oxygen (k_T) for the model system, that is, (k_T = 2.4 ± 0.2) × 10⁸ m ⁻¹ s⁻¹ without sodium cation vs (k_T = 6.9 ± 0.9) × 10⁷ m ⁻¹ s⁻¹ upon complexation of sodium cation to the crown ether. Furthermore, we found that the indole moieties undergo type I photooxidation processes with triplet excited methylene blue; this effect is also inhibited by the cation-π interaction. The chemical rate of reaction of the indole groups with singlet oxygen is also slower upon complexation of sodium cation in our model system, although we were unable to obtain an exact ratio due to differences of the chemical reaction rates of the two indole moieties.     

A two-configuration study on the photodetachment cross-section for the 3σu. channel of F 2 -*

An unusual resonance feature of the photodetachment cross-section for the 3σ_u channel of F₂ ^- observed in the early static-exchange study is confirmed by using correlated target (F₂) wavefunctions determined by configuration interaction (CI). The magnitude of the cross-sections is lowered from that in earlier calculation by the potential of the correlated target. Project supported by the National Natural Science Foundation of China and the State Education Commission of China.     

Design and synthesis of 3-acyl-2(3H)-benzoxazolone and 3-acyl-2(3H)-benzothiazolone derivatives

Abstract  

A simpler and efficient “green” method using solid sodium hydroxide in a solvent mixture of acetone/water was found to catalyze N-acylation of 2(3H)-benzoxazolones and 2(3H)-benzothiazolones for facile and rapid synthesis of N-acyl derivatives in excellent yields. This method was applied to the synthesis of a series of 132 compounds employing a variety of acyl chlorides.     

Glass-electrode measurements over a wide range of temperatures: The ionization constants (5–90°C) and thermodynamics of ionization of aqueous benzoic acid

Glass-electrode measurements have been applied to the determination of the ionization constant of aqueous benzoic acid from 5 to 90°C, with the experimental procedure and calculations described in detail. The results lead to ΔH^o=+60 cal-mole^?1 for the standard enthalpy of ionization at 298°K, which is compared with ΔH^o values from earlier investigations.