Daniela Consalvo

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.

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.

Rotational spectra of the 15N-aniline–X, (X=Ar, Ne) complexes. Structure determination from studies on isotopomers

Abstract The rotational spectra of the 15N-isotopomers of aniline–Ar and aniline–Ne have been studied in the frequency range 1–16 GHz. The structural analysis leads to a most probable structure with the rare gas atom in anti–position. It is on the side of the lone pair and shifted away from the nitrogen with respect to the center of mass of aniline. Argon is placed 3.52 A and neon 3.41 A above the phenyl ring.

Advances in Stark effect measurements in a molecular beam Fourier transform microwave spectrometer

For the first time Stark experiments in a pulsed nozzle Fourier transform microwave spectrometer are successfully performed with the pulsed molecular beam parallel to the resonator axis, together with a new geometry for the Stark electrodes which prevents line broadening due to E-field inhomogeneity. The coaxially oriented beam-resonator arrangement, introduced in the 1990s, is known to provide a considerable improvement in resolution and sensitivity in comparison to the perpendicular geometry, but Stark effect experiments performed in a microwave cavity, using the conventional cubic electrode geometry with this arrangement, suffer from an inhomogeneous field distribution. This gives rise to broadened profiles of the Stark shifted lines and a persistent zero-field line. The linewidth achieved with our new configuration is now close to the typical value found in the absence of a Stark field: less than 10 kHz at 10 GHz half width at half height, which makes the system very suitable for yielding precise valu...

The molecular structure of quinuclidine obtained by high resolution microwave spectroscopy

Abstract The rotational spectra of all 13C- and 15N- substituted isotopomers of quinuclidine (or 1-azabicyclo[2.2.2]octane, ABCO), C7H13N, in their natural abundance have been measured for the first time in the region 4–20 GHz employing pulsed molecular beam Fourier transform microwave spectroscopy (MB-FTMW). Their analysis yielded accurate rotational constants which allowed to determine the ground state heavy atom rs structure and the global r0-structure.

THE ELECTRIC DIPOLE MOMENT OF TETRAHYDROPYRAN-WATER

Abstract Using Stark-effect Fourier-transform microwave spectroscopy, the electric dipole moment components of tetrahydropyran–H 2 O were measured to be | μ a |=1.6034(3) D and | μ c |=0.9881(11) D. The a- and c-type spectra of the complex were observed. No b-type spectrum was found, consistent with ab initio geometries, which have a plane of symmetry in this hetero-dimer. Supported by these findings the μ b component of the dipole moment was fixed to zero. Adjusting the two remaining components, the Stark splittings can be reproduced within the experimental uncertainty. The ab initio dipole calculation, performed using the MP2/Spackman basis, shows that the measured dipole moment is only consistent with an axial–anti-configuration of the complex.