Jaap Bulthuis

Electrostatic deflection of the water molecule: A fundamental asymmetric rotor.

An inhomogeneous electric field is used to study the deflection of a supersonic beam of water molecules. The deflection profiles show strong broadening accompanied by a small net displacement towards higher electric fields. The profiles are in excellent agreement with a calculation of rotational Stark shifts. The molecular rotational temperature being the only adjustable parameter, beam deflection is found to offer an accurate and practical means of determining this quantity. A pair of especially strongly responding rotational sublevels, adding up to ≈25% of the total beam intensity, are readily separated by deflection, making them potentially useful for further electrostatic manipulation.

Water vapor at a translational temperature of 1 K

We report the creation of a confined slow beam of heavy-water (D{sub 2}O) molecules with a translational temperature around 1 K. This is achieved by filtering slow D{sub 2}O from a thermal ensemble with inhomogeneous static electric fields exploiting the quadratic Stark shift of D{sub 2}O. All previous demonstrations of electric-field manipulation of cold dipolar molecules rely on a predominantly linear Stark shift. Further, on the basis of elementary molecular properties and our filtering technique we argue that our D{sub 2}O beam contains molecules in only a few rovibrational states.

An NMR study of phosphoryl fluoride oriented in a nematic phase

Abstract The NMR spectrum of POF 3 in the nematic phase of EBBA has been measured at various temperatures. If the spectral data are interpreted in terms of a relative geometry, a deviation from the electron diffraction structure of 3° in the FPF angle is found. This discrepancy can be lifted by either assuming that the molecule distorts slightly on orientation, or by invoking large anisotropies in the indirect couplings. Quantitative estimates for both possibilities are given.

Temperature-dependent T1 measurements of 13C and 14N in acetonitrile dissolved in a thermotropic liquid crystal

The methyl 13C and the 14N longitudinal relaxation times in acetonitrile, dissolved in a thermotropic liquid crystal, were studied as a function of temperature under the condition of proton decoupling. The 14N longitudinal relaxation time could be derived from the cyano 13C linewidth due to the incomplete averaging of the dipolar interactions in the nematic phase. The correlation times for the reorientation of the 13CH vector and for the reorientation about an axis perpendicular to the principal molecular axis were obtained using standard relaxation theory, with allowance for the ordering in the nematic phase and applying extreme narrowing arguments. The results strongly indicate that the equations derived for the isotropic phase, assuming rotational diffusion, cannot be applied to a molecule dissolved in a nematic phase merely by taking into account the partial orientation.

NMR relaxation in CH3CN in a nematic solution under sample rotation. Frequency-dependent measurements

The relation between the T1(14N) and the cyano-1`3C linewidth of acetonitrile dissolved in a liquid crystal is investigated by slowly spinning the sample around an a/is perpendicular to the magnetic field direction. Results of frequency-dependent measurements and the activation energy of the rotational viscosity are reported.

Magnetic susceptibility anisotropies of small molecules measured by NMR

Abstract The anisotropy of the diamagnetic susceptibility of molecules can be derived from the alignment induced by the magnetic field of the NMR spectrometer. Up to now, only molecules with relatively large values of ⋯Δ χ ⋯ could be studied. The method is extended to smaller molecules by using relaxation data.

Fast-Gated Intensified Charge-Coupled Device Camera to Record Time-Resolved Fluorescence Spectra of Tryptophan

The possibilities of a 200 ps gated intensified charge-coupled device (CCD) camera to record time-resolved fluorescence were explored using the fluorescing amino acid tryptophan and its derivative N-acetyl-tryptophan amide (NATA) as model compounds. The results were compared to complementary data from time-correlated single-photon counting (TCSPC) experiments. If a spectral resolution of 1–2 nm is desired, the fast-gated intensified CCD (ICCD) camera is the method of choice. For a 10−5 M tryptophan solution, time-resolved emission spectra and intensity decays (measured over 12 ns at 25 ps resolution) could be obtained in typically 10 minutes, giving the well-known lifetimes of 0.5 and 3 ns. In addition, a longer lifetime of 7 ns was found at the red edge of the spectrum. The very short gate time of the ICCD camera allowed us to observe a shift in the emission maximum of tryptophan even within the first nanosecond of decay of the fluorescence emission. As expected from the tryptophan rotamer model, such a shift is not observed in NATA. Using amplitudes obtained by global analysis, decay-associated spectra of these lifetimes were constructed.

Electric-field-induced changes in spin-lattice relaxation in polar liquids

Abstract Spin—lattice relaxation times of acetonitrile, aligned by an electric field, have been measured. In contrast to earlier investigations on other polar liquids, no electric-field effects on T 1 could be established. The apparent discrepancy is discussed in terms of electric conduction and inhomogeneity of the applied electric field.

An NMR investigation of partially oriented CHF3 and CH2F2 including 13C satellites

Abstract In order to investigate the molecular geometries and the anisotropies of the indirect couplings, the NMR spectra including the 13C satellites of partially oriented CHF13 and CH2F2 have been measured. In CHF3 discrepancies have been found which can be attributed to small anisotropies in indirect couplings. The NMR geometry of CH2F2 calculated with neglect of vibrational motions and pseudodipolar couplings compares well with the MW structure. A marginal improvement has been obtained by taking these effects into account. IfJHF is assumed to be positive, JCF is negative in both molecules.

Prediction of the enthalpy of transfer of alkali-metal halides in binary mixtures

The quasi-lattice quasi-chemical model has been modified in order to predict the enthalpy of transfer of alkali-metal halides in binary solvent mixtures from the solvation properties in the pure solvents and from the excess enthalpy and Gibbs energy of mixing of the solvents. In mixtures with a negative Gibbs energy of mixing, there is an approximately linear dependence of the enthalpy of transfer on the mole fraction. In mixtures with a positive Gibbs energy of mixing, the occurrence of an extremum in the enthalpy of transfer is predicted.