Millimeterwave spectroscopy of transient molecules produced in a DC discharge

The construction of a millimeterwave spectrometer to study the pure rotational spectra of transient molecules in the gas phase is presented. The spectrometer is a source-modulated system combined with a free space glass discharge cell. Millimeterwave radiation has been produced using a frequency multiplier, the fundamental radiation source being klystrons. The spectrometer has been used to study the millimeterwave spectrum of carbon monosulfide (CS) and fluorine cyanide (FCN) produced inside the cell in a low pressure DC discharge of precursor gases. The quadrupole hyperfine structures of³³S and¹⁴N nucleus of CS and FCN have been resolved, measured and analysed.     

8 mm收发组件信号分析

主要研究8mm波段,雷达FMCW信号的时域及频域特性,通过对理论值与实测值的比较、分析,验证了8mm收发模块的可行性,并为下级信号处理作了准备。     

Q-band injection-locked gunn diode oscillator

The configuration and performance of a Q-band injection-locked Gunn oscillator are presented whose outport is connected with a phase-locked reference source by a circulator. The output power of the oscillator is more than 60mW at 46.1GHz. The single-sideband phase noise (SSB) is less than-71.7dBc/Hz offset 10KHz from the carrier, and the spectrum of clutter signal is less than -40dB.     

An electronical system for real-time measurement of the logarithmic magnitude of scattering parameters

An electronical system for real-time measurement of scattering parameters of millimeterwave two-ports is described. In order to achieve a suitable measurement accuracy, the output signals of the millimeterwave detectors and the characteristic of the measurement amplifier should be matched. For this reason the detector power-characteristic is approximated by help of a polygon and it is realized with a few nonlinear amplifiers. The theoretical background and experimental results show the applicability of the measurement system presented here.     

Helicity injection and diagnostics for orbitron millimeter wave source

Conventional orbitrons utilize the radially injected electrons for production of electromagnetic waves. In such a scheme, however, more than half of the electrons would not participate in the orbital motion around the anode due to the lack of acceleration. Only the electrons who did not suffer collisions till the radius 2/3 of the outer conductor (cathode) radius are possible to acquire the azimuthal velocity, via collisions, as large as the critical velocity with which the electrons can undergo circular equilibrium orbits. The axisymmetric injection is also a problem; 50% of electrons would be lost directly to the anode by the head-on collisions. This paper discusses various ways to enhance the efficiency and absolute power of an orbitron millimeterwave source. Experimental results are described on employment of a tapered metal-end, tangential injection of a thin electron beam, axial injection of rotating annular electron beams, and application of external magnetic fields. Further problem of conventional orbitrons is in its construction in which the potential-well is prematurely destroyed due to the shortening discharge current. Its diagnostics and consequence are discussed together with a new scheme leading towards the goal, an efficient injection of helicity (or helical electron-beam) into the potential-well conserved orbitron interation region.     

High-resolution FTIR and MMW study of the v4 = 2 (A1, E) excited state of NF3 near 985 cm: the axial ground state rotational constants derived by the “loop-method”

The two substates v₄ = 2⁰ (A₁, 983.702 cm⁻¹) and v₄ = 2^±2 (E, 986.622 cm⁻¹) of the oblate symmetric top molecule, ¹⁴NF₃, have been studied by high-resolution (2.5 × 10⁻³ cm⁻¹) infrared spectroscopy of the overtones and 2ν₄ − ν₄ hot bands. Transitions of the overtone, the hot band, and the previously measured fundamental band were combined to yield 585 ground state combination differences differing in K by ±3, with K_max = 36. Using the “loop-method,” a fit (standard deviation σ = 0.320 × 10⁻³ cm⁻¹) provided a complete set of the hitherto not experimentally known axial ground state constants. In units of cm⁻¹ these have the following values: . Upper state parameters were determined using a vibrationally isolated model. Considering l (2, 2) and l (2, −1) interactions between the v₄ = 2⁰ and v₄ = 2^±2 substates and effects accounting for the l (4, −2) interactions within the kl = −2 levels, 25 upper state parameters were obtained by fitting 2747 IR data (1842 transitions, 905 deduced energies, J_max = 42, K_max = 39) with σ_IR = 0.353 × 10⁻³ cm⁻¹. Moreover, millimeter-wave spectroscopy furnished 86 transitions (J_max = 16, K_max = 13) measured on the v₄ = 2 excited state. A merged fit, refining 24 parameters using the described model gave σ_IR = 0.365 × 10⁻³ cm⁻¹ andσ_MMW = 0.855 × 10⁻⁶ cm⁻¹ (26 kHz). The anharmonicity constants (in cm⁻¹) are x₄₄ = −0.84174 (2) and g₄₄ =  + 0.73014 (1). In addition to this model, the D, Q, and L reductions of the rovibrational Hamiltonian were tested. Standard deviations σ_IR = 0.375 × 10⁻³ cm⁻¹ and σ_MMW = 0.865 × 10⁻⁶ cm⁻¹ were obtained for both D and L reductions, and σ_IR = 0.392 × 10⁻³ cm⁻¹ and σ_MMW = 0.935 × 10⁻⁶ cm⁻¹ for Q reduction. The unitary equivalence of the majority of the 18 tested relations between the derived parameters was satisfactorily fulfilled. This confirms that the v₄ = 2 excited vibrational state can be considered in reasonable approximation to be isolated.     

Millimeterwave rotational spectrum and internal rotation in o-chlorotoluene

The millimeterwave rotational spectrum of o-chlorotoluene is investigated in the frequency region 150-250 GHz. Many rotational lines show splitting due to internal rotation of the methyl group. The analysis of the internal rotation splitting allows us to determine with precision the potential barrier to internal rotation of the methyl group. However, it is found that the moment of inertia of the methyl top is probably much smaller than usually assumed, which significantly affects the value of the barrier. Accurate centrifugal distortion constants are obtained for the ground states of ³⁵Cl and ³⁷Cl isotopologues as well as for an excited vibrational state.     

Rotational spectrum, structure and internal rotation in CH3CCl3

The rotational spectra of the v₆ = 1 and v₆ = 2 torsional states of CH₃C³⁵Cl₃ have been measured in the millimeterwave range and accurate spectroscopic constants have been determined. The equilibrium structure, the torsional frequency and the barrier to internal rotation have been calculated ab initio. These results are shown to be compatible with the absence of splittings in the rotational spectra.     

Rotational spectrum and bending potential of LiOH: A semirigid bender analysis

Some 29 microwave transitions in the millimeter region have been measured in the high-temperature vapor of LiOH, ranging up toJ=5, including lines from the isotopomers⁷Li¹⁶OH,⁷Li¹⁶OD in both ground and excited bending states, and⁷Li¹⁸OH in the vibrational ground state only. An analysis of these transitions, together with nine previously known radio-frequency transitions, based on the semirigid bender model of vibration-rotation interaction has been used to investigate the form of the bending potential and to measure the semirigidity parameters that show the variation in the bond lengths that accompany the large-amplitude bending motion. The molecule was found to be linear in its equilibrium configuration, with an essentially harmonic bending potential. The experimentally derived quadratic semirigidity parameter for the Li-O bond was found to agree to within less than 5% with that from an ab initio calculation at the MP3/6-311G^** level.