FURTHER ON THE PROBLEM OF REGIONAL ENTERITIS

No abstract

LIVER INJURY

No abstrac

STRATEGY OF DIAGNOSIS, PROGNOSIS AND MANAGEMENT OF ACUTE DESTRUCTIVE PANCREATITIS

No abstrac

OPERATIONS COMBINED WITH VAGOTOMY IN THE TREATMENT OF DUODENAL ULCER

No abstrac

RARE LOCALIZATIONS OF ECHINOCOCCUS CYSTS

No abstract

Velocity-selected molecular pulses produced by an electric guide

Electrostatic velocity filtering is a technique for the production of continuous guided beams of slow polar molecules from a thermal gas. We extended this technique to produce pulses of slow molecules with a narrow velocity distribution around a tunable velocity. The pulses are generated by sequentially switching the voltages on adjacent segments of an electric quadrupole guide synchronously with the molecules propagating at the desired velocity. This technique is demonstrated for deuterated ammonia (ND$_{3}$), delivering pulses with a velocity in the range of $20-100\,\rm{m/s}$ and a relative velocity spread of $(16\pm 2)\,$ at FWHM. At velocities around $60\,\rm{m/s}$, the pulses contain up to $10^6$ molecules each. The data are well reproduced by Monte-Carlo simulations, which provide useful insight into the mechanisms of velocity selection.Comment: 8 pages, 6 figure

CONFORMATION STUDY OF EPHEDRINE AND 2-PHENYLETHANOL AND THEIR HYDRATED CLUSTERS BY MASS SELECTIVE HIGH-RESOLUTION UV SPECTROSCOPY AND AB INITIO CALCULATIONS

{S. Chervenkov, P. Q. Wang, J. E. Braun, and H. J. Neusser \textit{J. Chem. Phys.{P. Butz, R. T. Kroemer, N. A. Macleod, and J. P. Simons \textit{J. Phys. Chem. AAuthor Institution: Physikalische und Theoretische Chemie, Technische Universitat Munchen, Lichtenbergstr. 4, D-85748 Garching, Germany; Department of Chemistry, Indian Institute of Technology Kanpur, UP 208016, IndiaA promising approach to the understanding of the interaction mechanisms and intrinsic properties of biological systems is the spectroscopic investigation of their conformational structures and dynamics at molecular level in the gas phase. Recently we measured the first resonance-enhanced two-photon ionization (R2PI) spectra with rotational resolution (70 MHz FWHM laser bandwidth) and mass selection of almost all vibronic bands of the S$_1$$\longleftarrow$S$_0$ electronic transition in the range between 37500 \wn and 37650 \wn for two biologically relevant molecules, ephedrine (C$_{10}$H$_{15}$NO)} \textbf{121}, 7169 (2004).}, and 2-phenylethanol (C$_8$H$_{10}$O), in a cold molecular beam. Employing a computer-assisted fit based on genetic algorithms for the analysis of the experimental rotational structures we determined the rotational constants for the ground S$_0$ and the first excited S$_1$ electronic states, respectively, and the transition moment ratios. To aid the unambiguous determination of the discussed conformations} \textbf{105}, 544 (2001).} of the observed species we performed \textit{ab initio} calculations on their structures and energies. The experiment corroborates the predictions that the most abundant conformers of ephedrine and 2-phenylethanol are the \textit{gauche} ones, stabilized by the intramolecular hydrogen-bonding interaction of their side-chains with the $\pi$ electrons of the aromatic ring. As a further step towards the investigation of these species in a biologically more realistic environment we started high-resolution experiments of the water complexes of ephedrine and 2-phenylethanol. The new results avail to a better insight into the intra- and intermolecular hydrogen bond formation and the influence of the solvent upon the conformational structure of these molecules

High-resolution ultraviolet spectroscopy of p-fluorostyrene-water: evidence for a σ-type hydrogen-bonded dimer

Ab initio calculations predict four stable conformational structures of the singly hydrated cluster of p-fluorostyrene: two out of plane with π- and two in plane with σ-type intermolecular hydrogen bonding between p-fluorostyrene and water. We employed mass-selective resonance-enhanced two-photon ionization high-resolution (70-MHz FWHM laser bandwidth) spectroscopy to partially resolve the rotational structure of the 000 origin band of the S1←S0 electronic transition. A computer-aided fit based on genetic algorithms was used to analyze the experimental high-resolution spectrum and to determine the observed conformational structure. The good agreement between the experimental and the simulated spectra of the 000 band and the assignment of the other prominent bands as inter- and intramolecular vibrational progressions clearly demonstrates that the anti in-plane conformer is the most abundant one in the molecular beam. The existence of the σ-type hydrogen bond between p-fluorostyrene and water manifests that the electron attracting effect of fluorine dominates over the releasing mesomeric effect of the vinyl group and thus a π-type hydrogen bonding with the aromatic ring is not favored in this case