H. Dreizler

A multioctave coaxially oriented beam‐resonator arrangement Fourier‐transform microwave spectrometer

The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier‐transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase‐inversion scheme and the low‐noise receiving system employing image‐rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in h...

An automatic molecular beam microwave Fourier transform spectrometer

We present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB‐MWFT) spectrometer used in the Kiel microwave group. We emphasize an automatic scanning facility which greatly increases the efficiency of MB‐MWFT spectroscopy for the measurement of unassigned spectra.

Construction of a molecular beam Fourier transform microwave spectrometer used to study the 2,5-dihydrofuran-argon van der Waals complex

Abstract The rotational spectrum of the van der Waals complex consisting of argon and 2,5-dihydrofuran has been observed in a molecular beam Fourier transform microwave spectrometer in the frequency range 5–18.5 GHz. Analysis of the derived spectroscopic constants shows that the dimer has a structure with a plane of symmetry in which the argon atom is located 3.48 A above the ring plane. The experimental setup of the molecular beam Fourier transform microwave spectrometer is also presented.

Microwave spectra of nitromethane and D3-nitromethane

Abstract The microwave spectra of isotopic nitromethanes are presently being reinvestigated in order to increase our understanding of the interaction between the almost free internal rotation and the vibrations. The presence of relaxation terms depending on cos3p proves that the symmetry of H eff is D 3h and furthermore makes a determination of the structure of the methyl group possible.

A newly designed molecular beam Fourier transform microwave spectrometer in the range 1–4 GHz

We report on a new design for a Fourier transform microwave spectrometer in the spectral region 1–4 GHz, specially constructed for the investigation of rotational spectra of heavy van der Waals complexes. In contrast to the commonly known molecular beam spectrometers using a Fabry–Perot resonator working with TEM00q modes, the proposed design employs a different type of resonator operating with TE01q modes. This resonator allows for compact dimensions even at cut‐off wavelengths above 0.1 m. Details of the design, performance data, and example spectra of stable molecules and complexes are given.

Microwave spectrum, barrier to internal methyl rotation, dipole moment, and partial structure of dimethylketene

Abstract From the microwave spectrum of dimethylketene which has been recorded from 8 to 37 GHz, the following rotational constants were derived: A = 8 267.832 ± 0.8, B = 3 884.101 ± 0.03, C = 2 728.826 + 0.03 MHz. The dipole moment is μ a = 1.94 ± 0.01 D. Substitution coordinates for all methyl group atoms have been obtained by investigating the spectra of six isotopic species of the molecule. The potential barrier V 3 hindering internal rotation of the methyl tops has been fitted to the multiplet width of a number of high- J ground state a Q -transitions which were observed as triplets. V 3 is 2065 cal/mole, keeping fixed I α = 3.132 amu A 2 and angle (methyl-top to a -axis) = 58.94° as obtained from the partial substitution studies.

Mikrowellenspektrum, Struktur, Dipolmoment und internes Hinderungspotential von Dimethyldisulfid

The microwave spectra of CD3 —S —S —CD3 and CH3 —S —S—CH3 have been measured in the frequency range from 5.5 to 34 kmc/sec. From the six rotational constants an r0-structure has been calculated. STARK-effect measurements have been made for the 101 —110 and 202—211 rotational transitions of CH3—S—S—CH3. The dipole moment was calculated to be (1.985±0.01) Debye. An approximate value for the barrier to internal rotation of the two methyl tops is given, V3= (1.6±0.1) kcal. The calculation has been based on triplet splittings of the rotational lines using second order perturbation theory in the torsional wavefunctions and neglecting first order and cross terms in angular momentum.

A microwave Fourier Transform Spectrometer in the range of 5.4 to 8 GHz

Abstract We describe in detail the construction of a Microwave Fourier Transform Spectrometer and demonstrate the achievable linewidth.

Microwave Fourier‐transform spectrometer for the entire K band for the investigation of rotational spectra of molecules in the gas phase

We present the experimental set up of a microwave Fourier‐transform spectrometer for the entire K band from 18 to 26.4 GHz. It is hereby shown that this type of spectroscopy is achieved above 18 GHz. Advantages and disadvantages are discussed. The performance is illustrated by the recordings of rotational transitions of various molecules.

Structure of aniline–X (X=Ar, 20Ne, 22Ne) from high resolution microwave spectroscopy data

Abstract The rotational spectra of aniline, C 6 H 7 N, complexed with Ar, 20 Ne and 22 Ne were measured for the first time in the spectral region 1–18 GHz employing pulsed molecular beam Fourier transform microwave spectroscopy (MB-FTMW). Their analysis yielded rotational, centrifugal distortion and 14 N quadrupole coupling constants for the respective van der Waals complexes. The cluster structure was evaluated by the r 0 - and r s -methods. In addition a specific model was applied which takes the van der Waals bending vibrations into account. Four possible positions of the rare gas atom are consistent with the moments of inertia of the complex. From the diagonal elements of the two Ne isotopomers the off-diagonal element χ ab and subsequently the principal nitrogen coupling tensor elements could be evaluated, too.