Impulsive rotatory motion of a circular disk in a viscous fluid

Zusammenfassung Es wird eine analytische Methode für die Bestimmung der Geschwindigkeit der Strömung und der Winkelgeschwindigkeit einer kreisförmigen Scheibe gegeben, die in einer zähen, inkompressiblen Flüssigkeit einen Drehstoss erhält.

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This research was sponsored by the US. Army under contract no. DA-11-022-ORD-2059 with the University of Wisconsin.     

Kinetic studies on the formation of N-nitroso compounds X. The nitrosation ofN-methylacetamide and its differences with respect to the nitrosation of amines

The kinetics of the nitrosation ofN-methylacetamide have been studied using spectrophotometry. Significant differences with respect to the mechanism of nitrosation of amines were observed: the absence of catalysis by halides, the existence of general basic catalysis by acetate and its chlorated derivatives obeyingBrønsted's law (with =0.49), and the primary isotopic effect (with a ratio of 7.9 between the rate constants for the elementary process in H₂O and D₂O). All this indicates that the slow step of the mechanism must be the transfer of a proton from the protonated nitrosamide to the reaction medium.

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Kinetische Untersuchungen zur Bildung von N-Nitroso-Verbindungen, 10. Mitt.: Die Nitrosierung vonN-Methylacetamid und die Unterschiede in bezug auf die Nitrosierung von Aminen

Zusammenfassung Die Kinetik der Nitrosierung vonN-Methylacetamid wurde mittels Spektrophotometrie untersucht. Es wurden signifikante Unterschiede zum Mechanismus der Nitrosierung von Aminen beobachtet: die Abwesenheit einer Katalyse durch Halogenide, die Existenz einer generellen basischen Katalyse durch Acetat und dessen chlorierten Derivaten unter Übereinstimmung mit demBrønstedschen Gesetz (mit =0,49) und einem beobachtbaren Isotopeneffekt (mit einem Verhältnis von 7,9 zwischen den Geschwindigkeitskonstanten in H₂O und D₂O). All das zeigt an, daß der geschwindigkeitsbestimmende Schritt im Mechanismus der Transfer eines Protons vom protonierten Nitrosamid zum Reaktionsmedium sein muß.

     

Coordinative and electrostatic forces in action: from the design of differential chromogenic anion sensors to selective carboxylate recognition

A new family of differential chromogenic anion chemosensors is described based on anilinopyridine-metal cation coordinative signalling ensembles.     

Neodymium(III)-substituted bismuth titanate thin film generation using metal alkoxo, acyloxo, and beta-diketonato precursors employing a sol-gel route and using 4f-4f transition spectra as probes to explore kinetic performance

Heterotrimetallic lanthanide-substituted bismuth titanate (BLT, where lanthanide is neodymium) with stoichiometry Nd(0.75)Bi(3.25)Ti(3)O(12) has been obtained in both highly homogenized crystalline and amorphous thin film forms using three different multicomponent precursors, A (formed from Nd(OC(3)H(7)(i))(3), Bi(OOC.CH(3))(3), and Ti(OC(3)H(7)(i))(4) taken in the desired stoichiometry), B (formed from Nd(OC(3)H(7)(i))(2)(acac), Bi(OOC.CH(3))(3), Ti(OC(3)H(7)(i))(3)(acac)), and C (formed from Nd(OC(3)H(7))(acac)(2), Bi(OOC.CH(3))(3), Ti(OC(3)H(7))(3)(acac), in the desired stoichiometry), and employing controlled acidic hydrolysis during the sol-gel method. Paramagnetic Nd(III), an f(3) metal ion, gives characteristic 4f-4f transition spectra in the visible and near infrared region. The sensitivity of 4f-4f transitions to minor coordination changes around paramagnetic Nd(3+) has been used to monitor hydrolysis during the progress of the sol-gel process of the multicomponent BLT precursors. The variation of intensities (oscillator strengths) of 4f-4f bands during hydrolysis, as well as the variation of Judd-Ofelt intensity parameters, has helped in following the preliminary kinetics of hydrolysis. Highly complex polycondensation reactions occurred during sol-gel hydrolysis of three BLT precursors. Rates of hydrolysis with respect to five 4f-4f transitions of Nd(III) were determined. The different types of multicomponent BLT precursors have shown different rates of hydrolysis, following the reactivity trend A > B > C.     

Fourier transform emission spectroscopy and ab initio calculations on NbCl

The emission spectrum of NbCl has been recorded in the 3000-20 000 cm⁻¹ region using a Fourier transform spectrometer. The bands were observed by microwave excitation of a mixture of NbCl₅ vapor and He. Two groups of bands observed in the 6500-7000 cm⁻¹ and 9800-11 000 cm⁻¹ regions have been assigned to two electronic transitions. Five bands observed in the 6500-7000 cm⁻¹ region consist of R, P, and Q branches with no combination defect or Λ-doubling. They have been assigned as five sub-bands of a ΔΛ=±1 transition with Λ>1. Nine bands observed in the 9800-11 000 cm⁻¹ regions consist of R and P branches, and they are also free from Λ-doubling. These bands have been classified into four sub-bands of a ΔΛ=0 transition (with Λ>1), which has tentatively been assigned as . The two transitions have no electronic states in common. Ab initio calculations have been performed on NbCl and the spectroscopic properties of the low-lying electronic states have been calculated. The ground state of NbCl has been predicted to be a state arising from the 3σ¹ 1δ² 2π¹ configuration, with a low-lying state at 1300 cm⁻¹ from the 3σ¹ 1δ¹ 2π² configuration. The results of our experimental and theoretical studies will be presented. This work represents the first experimental investigation of the spectra of NbCl and the first ab initio prediction of the spectroscopic properties of the low-lying electronic states.     

Infrared emission spectroscopy of a new Σ-Σ system of TiCl

The spectra of TiCl have been reinvestigated in the 4200-8500 cm⁻¹ region using the 1-m Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. The molecules were excited in a microwave discharge lamp operated with 3.0 Torr of He and a trace of TiCl₄ vapor, and the spectra were recorded at a resolution of 0.01 cm⁻¹. Three new bands with origins near 6938.9, 6900.2, and 6861.7 cm⁻¹ have been assigned as the 0-0, 1-1, and 2-2 bands of a new - transition. This assignment is supported by our recent ab initio calculations on TiCl and ZrCl [J. Chem. Phys. 114 (2001) 3977]. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted for the states.