E. Fliege

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.

Refinement of the deuterium quadrupole coupling in D15NO3: Combined experimental and theoretical results

Abstract In this paper we present improved values for the quadrupole coupling tensor of nitric acid D 15 NO 3 obtained from microwave Fourier transform spectroscopy and ab initio calculations. Whereas the experiment yields more accurate values of the coupling tensor than the calculation, the latter gives additional information, e.g., the off-diagonal element not amenable to the experiment.

Internal rotation and 14N quadrupole coupling of 3- and 5-methylisoxazole

Abstract In the following we present a 14 N quadrupole hyperfine structure, a fourth-order centrifugal distortion, and an IAM methyl internal rotation analysis of 3- and 5-methylisoxazole. The measurements were done in the frequency range of 8 to 26 GHz employing a microwave Fourier transform spectrometer.

A Contribution to the Microwave Spectrum of Dimethyl Selenide

Abstract The microwave spectra of five isotopic species of dimethyl selenide have been measured and analysed for centrifugal distortion and internal rotation by PAM and IAM.

Two-Dimensional Microwave Fourier Transform Spectroscopy

We performed a pulse sequence experiment utilizing a technique, which is comparable with two-dimensional NMR-spectroscopy. Some theoretical considerations based on the three-level Bloch equations are given. This double resonance technique may be useful for the assignment of complicated spectra.

Vibronic Ground State Rotational Spectrum of 3-Bromothiophene

The rotational spectrum of 3-bromothiophene was investigated in the frequency range between 8 and 18 GHz by use of a microwave Fourier transform spectrometer. Both a- and b-type spectra were assigned for the vibronic ground state. Rotational constants, quartic centrifugal distortion constants and quadrupole coupling constants were obtained for the 79Br- and 81Br-isotopic species. For the analysis, the effective rotational Hamiltonian including centrifugal distortion in the form of Van Eijcks symmetric top reduction and bromine quadrupole coupling was set up in the coupled basis of the limiting symmetric top, J, K, I, F, MF>, and was diagonalized numerically. Spin rotation interaction was neglected

A Reanalysis of 14N Nuclear Quadrupole Coupling and Methyl Internal Rotation in the Rotational Spectra of Monomethyl Oxazoles and Isoxazoles

Abstract Previously published rotational frequencies of 2-, 4-, and 5-methyl oxazole and of 3- and 5-methyl isoxazole are reanalysed to obtain correct rotational constants (A constants in the first place) on the basis of hypothetically unsplit rotational centre frequencies. With these, r0-structural parameters of the respective methyl group could be determined, thus allowing us to consider the influence of methyl substitution on the 14N-quadrupole coupling tensor and the structural relevance of the internal rotor angle given by torsional analysis. 14N nuclear quadrupole hfs and IAM methyl torsional analyses were redone with the correct rotational constants.

A Reinvestigation of the Rotational Spectrum of 2-Chloropropene

The microwave spectrum of 2-chloropropene was reinvestigated using microwave Fourier transform spectroscopy. For the two isotopic species CH3C35Cl=CH2 and CH3C37Cl=CH2 the chlorine quadrupole coupling was determined with higher accuracy. The barrier to internal rotation was determined from the ground state. For comparison the first excited torsional state of CH3C35Cl=CH2 was remeasured and reanalysed

14N Nuclear Quadrupole Coupling and Methyl Internal Rotation of 2-, 4-, and 5-Methyl Oxazole

In the following we give an outline of 14N nuclear quadrupole, internal axis method (IAM) methyl internal rotation, and fourth order centrifugal distortion - only needed for extrapolating transition frequencies to higher J values - analyses performed for 2-, 4-, and 5-methyl oxazole. The results are discussed, the three methyl oxazoles being compared with one another and with their common parent, oxazole.

Deuterium Quadrupole Coupling in Cyanoacetylene. An Application of Microwave Fourier Transform Spectroscopy

Only few molecules have been investigated for deuterium hyperfinestructure (d-hfs) by microwave spectroscopy. The d-hfs of some additional molecules was analysed by beam methods (beam maser spectroscopy, molecular beam electric resonance spectroscopy). For a detailed bibliography see Landolt-Börnstein [1, 2] . By use of Microwave Fourier transform Spectroscopy [3, 4] we are able to increase the resolution of standard microwave spectroscopy because modulation and saturation broadening effects are avoided. Also Stark broadening by imperfect biasing of the Stark square wave is not present. With our spectrometer we are able to measure at low pressures. Pressure broadening can thus be minimized. Doppler and wall broadening are now limiting the resolution of our instrument. We investigated the / = 1 — 0 and 2 — 1 transitions of cyanodeuteroacetylene-N, D — C = C — CN. The prediction of the transitions was based on measurements of Mallinson and de Zafra [5] . The sample of D — C = C — CN was prepared by one of us (M.A.) by modifying published procedures [6, 7] . A sample of propynoic acid methyl ester (0.84 g) H C = C — C02CH3 from EGA CHEMIE, Steinheim, was dissolved in 2 ml of methanol and 2 ml D 20. The mixture was allowed to react at 213 K with liquid-ammonia N (0.34 g) from IC-Chemikalien München. After one hour of vigorous stirring the volatile products were pumped off at 1 mTorr until the product was very dry. The amide D — C = C — C0NHo was then dissolved in a