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

Directional coupling and branching of optical signals by dark beams

ABSTRACT Various types of dark optical beams with respect to their phase dislocation are discussed and their propagation dynamics is analyzed. On the basis of numerical results 1D and 2D optical couplers are proposed. The respective energy efficiencies for each of the output channels are estimated. Multiple charged optical vortices and their topological instability are presented. Through a proper type of perturbation applied to these vortices they could be split into several sub-beams, thus giving the opportunity of proposing all-optical branching schemes. Two output channel distribution schemes for such an optical brancher are discussed

NUMERICAL DESCRIPTION OF THE GROUNDWATER LEVELS CHANGE DUE TO THE RE- AND DISCHARGE OF THE ADJACENT SURFACE WATER BODIES – PROBLEMS AND CASE STUDIES

Numerical description of the groundwater levels change due to the re- and discharge of the adjacent surface water bodies – problems and case studies. The water exchange between the surface water bodies (rivers, lakes, seas, dams, etc.) and adjacent water-bearing beds is possible if a hydraulic connection between them exists. The change of the levels of the first ones causes corresponding changes of the levels of the aquifers in the surrounding territories and vice versa. In many cases this interaction is the primary mechanism determining the groundwater regime. The aim of the present study is to examine the applicability of the most general possible analytical approach for quantitative description of the phenomena in the case of short-term changes with a significant magnitude (high waves) of the level of the river of Maritsa in Plovdiv, Bulgaria. The study is performed through numerical simulations/calculations, with especially composed by the authors for this work computational programs

Competition between π and σ hydrogen bonds and conformational probing of 2-orthofluorophenylethanol by low- and high-resolution electronic spectroscopy

The flexible model molecule 2-orthofluorophenylethanol has been investigated by laser-induced fluorescence, and low- and high-resolution resonance-enhanced two-photon ionization spectroscopy in combination with high-level ab initio quantum chemistry calculations. One dominant conformation has been identified in the cold molecular beam corresponding to the most stable theoretically predicted gauchestructure stabilized by an intramolecular OH⋯π hydrogen bond. A tentative assignment of a higher-lying gauche conformer present in the molecular beam separated by high potential barriers from the most stable one has been made. The missing other higher-energy theoretically predicted conformations most likely relax to the most stable ones during the process of the adiabatic expansion. The good agreement between the experimental and theoretical results demonstrates that even in the case of a substitution with an electronegative atom at the ortho position, bringing about a significant redistribution of the electron density in the benzene ring and providing a convenient binding site for the formation of a competing OH⋯F σhydrogen bond, the nonclassical OH⋯π bond remains the preferred binding motif for the most stable conformer

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

Specific and nonspecific interactions in a molecule with flexible side chain: 2-phenylethanol and its 1:1 complex with argon studied by high-resolution UV spectroscopy

Using high-resolution resonance-enhanced two-photon ionization spectroscopy in combination with genetic-algorithm-based computer-aided rotational fit analysis and ab initio quantum chemistry calculations we determined the conformational structure and transition moment orientation in 2-phenylethanol and its 1:1 clusters with argon. The results clearly demonstrate that the gauche structure of 2-phenylethanol, which is stabilized by the intramolecular π-hydrogen bond between the folded side chain and the benzene ring, is the most abundant in the cold molecular beam. In this conformer the transition moment is rotated by 18° from the short axis of the aromatic ring. Two distinct 1:1 complexes of 2-phenylethanol with argon in a cis- and trans-configuration with respect to the side chain have been found. Employing the Kraitchman [Am. J. Phys.21, 17 (1953)] analysis we have found that the structure of the 2-phenylethanol moiety and the orientation of the transition moment do not change after the complexation with argon within the experimental accuracy. From the measured band intensities we conclude that in addition to the dispersion interaction of the argon atom with the aromatic ring a hydrogen-bond-type interaction with the terminal –OH group of the side chain stabilizes the cis-structure of the 1:1 complex of 2-phenylethanol with argon

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