Continuous-Wave Operation of a 460-GHz Second Harmonic Gyrotron Oscillator

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE(0,6,1) mode near 460 GHz. The gyrotron also operates in the second harmonic TE(2,6,1) mode at 456 GHz and in the TE(2,3,1) fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE(0,6,1) mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T.     

Mechanism of the oxidative carbonylation of terminal alkynes at the ≡C-H bond in solutions of palladium complexes

The formation mechanism of the active catalyst in the oxidative carbonylation of terminal alkynes at the ≡C-H bond has been investigated for the catalytic system Pd(OAc)₂-PPh₃-p-benzoquinone (Q)-MeOH. It has been demonstrated by NMR spectroscopy, X-ray crystallography, and kinetic measurements that the catalytically active palladium is in the oxidation state 0 and is bound into complexes stabilized by p-benzoquinone (PdL₂Q, where L = PPh₃). A mechanism is suggested for the catalytic process, which includes the formation of the complex PdL₂Q, the oxidative addition of the alkyne to this complex at the ≡C-H bond, the insertion of CO into the Pd-C bond, and steps in which hydride hydrogen is intramolecularly transferred to the p-quinone.     

On the shape of the Q-branch of Raman scattering spectra in dense media. Comparison with experiment

The theory of the isotropic Raman line broadening is compared with gas and liquid experimental data. The effect of rotational structure narrowing with increasing density is confirmed. The vibrational relaxation (dephasing) contribution to the spectral broadening has been extracted, it being essential in liquid phase. It has been shown to be due to weak collisions and to increase proportionally to their frequency.     

Nitroxyl-radical rotational-mobility anisotropy effects in magnetization-transfer electron spin echo

Formulas have been derived for the magnetization transport in the limiting case of uniaxial rotation and any reorientation correlation (Ivanov-Valiev model). Numerical calculations have been performed for particular situations. Rotational-mobility anisotropy makes itself felt when the difference in the angles between the symmetry axis for the nitroxyl radical magnetic tensor and the rotation axis is less than 30° or close to 90°.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 647–653, November–December, 1989.