Nonadiabatic transitions in electrostatically trapped ammonia molecules

Nonadiabatic transitions are known to be major loss channels for atoms in magnetic traps, but have thus far not been experimentally reported upon for trapped molecules. We have observed and quantified losses due to nonadiabatic transitions for three isotopologues of ammonia in electrostatic traps, by comparing the trapping times in traps with a zero and a non-zero electric field at the center. Nonadiabatic transitions are seen to dominate the overall loss rate even for samples at relatively high temperatures of 10-50 mK

THE STYRENE OXIDE DIMER STORY

The processes that govern aggregation at the molecular level are loosely established. Molecular recognition is mediated via a delicate balance between the prevailing intermolecular interactions at play, hydrogen bonding and dispersion interactions. Using high-resolution broadband rotational spectroscopy and supersonic jets, we studied the styrene oxide dimer. Due to its chirality, these dimers exist as enantiomeric and diastereomeric pairs, with the diastereomers being directly differentiable via their rotational spectra. Interestingly, the three most stable styrene oxide dimers are stabilized by three intermolecular contacts, arising from two CH-O and $\pi$-$\pi$ interactions. The phenyl groups show a similar arrangement as in the case of the parallel-displaced benzene dimer. The next set of dimers, which are slightly higher in energy, is stabilized by two CH-$\pi$ interactions each. The interplay between hydrogen bonding and dispersion on the formation of these homo- and heterodimers as well as their prospects for chiral tagging will be discussed

Interne Dynamik und Wechselwirkungen mit externen Feldern : rotationsspektroskopische und gruppentheoretische Untersuchungen

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Precise dipole moment and quadrupole coupling constants of benzonitrile

We have performed Fourier transform microwave spectroscopy of benzonitrile, without and with applied electric fields. From the field-free hyperfine-resolved microwave transitions we simultaneously derive accurate values for the rotational constants, centrifugal distortion constants, and nitrogen nuclear quadrupole coupling constants of benzonitrile. By measuring the Stark shift of selected hyperfine transitions the electric dipole moment of benzonitrile is determined to $\mu=\mu_a=4.5152 (68)$ D.Comment: 6 pages, 2 tables (elsart

A versatile electrostatic trap

A four electrode electrostatic trap geometry is demonstrated that can be used to combine a dipole, quadrupole and hexapole field. A cold packet of 15ND3 molecules is confined in both a purely quadrupolar and hexapolar trapping field and additionally, a dipole field is added to a hexapole field to create either a double-well or a donut-shaped trapping field. The profile of the 15ND3 packet in each of these four trapping potentials is measured, and the dependence of the well-separation and barrier height of the double-well and donut potential on the hexapole and dipole term are discussed.Comment: submitted to pra; 7 pages, 9 figure

CHIRALITY RECOGNITION IN CAMPHOR - 1,2-PROPANEDIOL COMPLEXES

The molecular interactions in complexes involving chiral molecules are of particular interest, because the interactions change in a subtle way upon replacing one of the partners by its mirror image. This is based on the fact that chiral molecules are sensitive probes for other chiral objects and chiral interactions. In this particular case, we will concentrate on molecule-molecule interactions and investigate them with broadband rotational spectroscopy. When two chiral molecules form complexes, the homochiral and heterochiral forms have different structures (and thus rotational constants and spectra) and different energies. They are diastereomers, which can easily be differentiated, for example via molecular spectroscopy. This is often exploited in chemical synthesis for identifying and separating enantiomers. _x000d_ The phenomena involving chirality recognition are relevant in the biosphere, in organic synthesis and in polymer design. _x000d_ _x000d_ We use chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy to study the structures and the underlying interactions of camphor-1,2-propanediol complexes. This system is also interesting because the complex formation can be expected to be ruled by an interplay between hydrogen bonding to the polar carbonyl group in camphor and dispersion interactions. The spectra are extremely rich because of the high number of conformers for 1,2-propanediol. We started out with racemic mixtures of both camphor and 1,2-propanediol. Using enantiopure samples of different handedness of the two partners nicely simplifies the spectra and guides the assignment. In the talk, we will report on the latest results for this chiral complex._x000d

A MINTY MICROWAVE MENAGERIE: THE ROTATIONAL SPECTRA OF MENTHONE, MENTHOL, CARVACROL, AND THYMOL

Terpenes represent one of the largest classes of secondary metabolites in nature and are derived from adding substituents to their core building block, isoprene. They exhibit a huge assortment of structures and thus a variety of chemical and biological activities. We recently investigated a number of monoterpenoids using broadband rotational spectroscopy in the 2-8.5 GHz frequency range. begin{wrapfigure}{r}{0pt} includegraphics[scale=0.7]{menthone_spec_2.eps} end{wrapfigure} We present a comparative study of the aromatic monoterpenoids thymol and carvacrol and aliphatic menthone and menthol. The differences in their electronic and steric structures significantly influence molecular properties such as internal rotation barriers and conformational flexibility. These influences are revealed in the rotational spectra. We report the rotational spectra and the experimentally determined molecular parameters. Results from extensive quantum chemical calculations of the conformational spaces of these molecules are compared with the experimentally determined molecular parameters

ON THE PHASE DEPENDENCE OF DOUBLE-RESONANCE EXPERIMENTS IN ROTATIONAL SPECTROSCOPY

We report double-resonance experiments using broadband chirped-pulse Fourier transform microwave spectroscopy that facilitate spectral assignment and yield information about weak transitions with high resolution and sensitivity. Using the diastereomers menthone and isomenthone as examples, we investigate both the amplitude and the phase dependence of the free-induction decay of the microwave signal transition from pumping a radio frequency transition sharing a common level. begin{wrapfigure}{l}{0pt} includegraphics[scale=0.8]{isomenthone_reg_phase.eps} end{wrapfigure} We observe a strong phase change when scanning the radio frequency through molecular resonance. The direction of the phase change depends on the energy level arrangement, i.e., if it is progressive or regressive. The experimental results can be simulated using the density-matrix formalism using the three-level Bloch equations and are best described with the AC Stark effect within the dressed-state picture, resulting in an Autler-Townes splitting. The characteristic phase inversion allows for a) the precise frequency determination of the typically weak radio frequency transitions exploiting the high sensitivity of the connected strong microwave signal transition and b) definitive information about the connectivity of the energy levels involved, i.e., progressive vs. regressive arrangements