High-resolution spectroscopy of C2H3D: Line positions and energy structure of the strongly interacting ν10,ν7,ν8,ν4 and ν6 bands.

High resolution infrared spectra of C2H3D were recorded in the region of 550-1950 cm-1 with a Bruker IFS125 HR Fourier transform infrared spectrometers and rotational structures of the five lowest strongly interacting ν10, ν7,ν8,ν4 and ν6 bands were analyzed. The number of about 28000 transitions (4200/6800/5600/5000/6400 for the bands ν10,ν7,ν8,ν4 and ν6) with Jmax = 40 and Kamax = 20 were assigned to these five bands. The weighted fit of 3990 upper energy values obtained from the experimentally recorded transitions was made with a Hamiltonian which takes into account resonance interactions between all studied bands as well as with the sixth ν3 band which was considered in this case as a "dark" one. As the result of analysis, a set of 279 fitted parameters was obtained which reproduces the initial 3990 upper "experimental" ro-vibrational energy values with the drms=1.7×10-4 cm-1; the initial nonsaturated, unblended and not very weak of 28000 assigned transitions are reproduced with the drms=2.2×10-4 cm-1. Ground state parameters of the C2H3D molecule were improved as well.

Ultraviolet photodissociation dynamics of PCl3 at 235 nm: three-dimensional ion imaging and theoretical analysis.

The photodissociation dynamics of PCl3 at 235 nm has been studied by monitoring ground state Cl(2P3/2) and spin-orbitally excited Cl(2P1/2) atoms by resonance enhanced multiphoton ionization (REMPI). Also, the PCln+ (n = 0, 1, 2) photoions were observed non-resonantly. The speed distributions and speed-dependent anisotropy parameters ß for all these particles have been determined by three-dimensional photofragment ion imaging. The ß parameters are close to zero for all these particles. The relative yield of excited Cl(2P1/2) atoms for photodissociation of PCl3 is 0.49 ± 0.03. The speed distributions of Cl(2P3/2) and Cl(2P1/2) atoms are bimodal, mainly resulting from the sequential photodissociation PCl3 → PCl2 → PCl. Near-resonant two-photon ionisation followed by near-resonance one-photon photodissociation is proposed for the production of PCln+ photoions. Using Condon's reflection principle, we constructed the vibrational mode dependent absorption spectrum by accounting for the vibrational motion for all six normal coordinates. As a result, the absorption of 235 nm radiation by PCl3 occurs due to zero vibrational motion rather far from the equilibrium geometry. In particular, movement along the Q2 normal coordinate results in an efficient photoinduced transition into the excited state à of D3h symmetry due to a parallel transition.

Double-arm three-dimensional ion imaging apparatus for the study of ion pair channels in resonance enhanced multiphoton ionization.

We present a novel experimental configuration for the full quantitative characterization of the multichannel resonance enhanced multiphoton ionization (REMPI) of small molecules in cases when the ion-pair dissociation channel is important. For this purpose, a double-arm time-of-flight mass spectrometer with three-dimensional (3D) ion imaging detectors at both arms is constructed. The REMPI of HCl molecules is used to examine the constructed setup. The apparatus allows us to perform simultaneous measurements of the 3D velocity vector distributions of positive (H(+), HCl(+), and Cl(+)) and negative (Cl(-)) photoions. The characterization consists of the determination of "two-photon absorption cross sections" for the process HCl(X)+2hν → HCl*, one-photon absorption cross sections for subsequent processes HCl* + hν → HCl*, and the probability of the subsequent non-adiabatic transition HCl* → HCl(B) → H(+) + Cl(-), which leads to ionic pairs. All these data should be obtained from the analysis of the dependencies of the number of ions on the laser energy. The full characterization of the laser beam and the knowledge of the ion detection probability are necessary parts of the analysis. Detailed knowledge of losses of produced ions in the mass spectrometer before detection requires understanding and characterization of such processes like electron emission from metallic grids under ion bombardment or charge transfer between positive ions and the metal surface of the grids, like Cl(+) + (grid) → Cl(-). These important phenomena from surface science are rarely discussed in the imaging literature, and here, we try to compensate for this shortcoming.

Simultaneous imaging of both product ions: exploring gateway states for HCl as a benchmark molecule.

Simultaneous imaging of both positive and negative product ions is used to exclusively study photoion pair formation free from interference of competing fragmentation channels. Resonance enhanced multi-photon excitation allows us to interrogate potential energy surfaces for vastly differing molecular geometries. 3D imaging provides complete fragment information. We applied the technique to HCl as a benchmark and identified the gateway state leading to photoion pairs. The approach can easily be applied to any molecule exhibiting a potential with an attractive part at large internuclear distances.

Proton formation dynamics in the REMPI[2+n] process via the F 1Delta2 and f 3Delta2 Rydberg states of HCl investigated by three-dimensional velocity mapping.

HCl in the bulk gas phase at a pressure of 10(-5) mbar has been excited via selected Q-lines of the two-photon transition band systems F (1)Delta(2)<--X (1)Sigma(+)(1,0) [Q(8)], V (1)Sigma(+)<--X (1)Sigma(+)(14,0) [Q(8), Q(7)] and f (3)Delta(2)<--X (1)Sigma(+)(0,0) [Q(2-6)]. Concerning the V<--X excitation, subsequent photon absorption is known to yield HCl(+), H(n=2)+Cl, H(+)+Cl(-) and H+Cl(4s,4p,3d). Vibrationally excited HCl(+) (v(+) > or = 5) can be photodissociated to H(+)+Cl, and excited atoms can be easily photoionized by absorption of a fourth photon, respectively. Using three-dimensional velocity map imaging, the spatial proton velocity distributions resulting from these processes for these particular transitions were studied for the first time. Kvaran et al. [J. Chem. Phys. 131, 044324 (2009); J. Chem. Phys. 129, 164313 (2008)] recently reported a substantial increase in the formation of chlorine and hydrogen ions in single rovibrational transitions of the F (1)Delta(2) and f (3)Delta(2) band systems using mass resolved resonance enhanced multiphoton ionization spectroscopy and explained this by the vicinity of single rovibrational levels of the V (1)Sigma(+) state for which photorupture is the main feature. Thus, the known dissociation dynamics of the V (1)Sigma(+) state should also leave their fingerprint in the spatial proton velocity distribution emerging from the photodissociation of those states. Accordingly, we found a strong increase in the H(+) ion signal for the Q(5) line of the f (3)Delta(2)<--X (1)Sigma(+)(0,0) transition, the extra signal resulting from dissociation into H(n=2)+Cl((2)P(1/2)) and the ion pair. No increase for the HCl(+)(v(+) > or = 5) photodissociation channel or dissociation into H(n=2)+Cl((2)P(3/2)) has been observed. Furthermore, H(+) distributions from the Q transitions of the f (3)Delta(2)<--X (1)Sigma(+)(0,0) band system were found to show the two features previously ascribed to the "gateway" state [(4)Pi...4s](3)Pi(0), i.e., autoionization into HCl(+)(5 < or = v(+) < or = 8) and nonadiabatic dissociation into H(n=2)+Cl((2)P(3/2)). The F (1)Delta(2)<--X (1)Sigma(+)(1,0) band system only showed significant proton formation for the Q(8) line. The speed distribution is the same as for the Q(8,7) lines of the V (1)Sigma(+)<--X (1)Sigma(+)(14,0) transition while the excitation history is conserved in the angular distribution confirming the resonance interpretation.

Measurement of the differential cross section of the photoinitiated reactive collision of O((1)D)+D(2) using only one molecular beam: A study by three dimensional velocity mapping.

In order to measure the state selective double differential cross section of a reactive collision, the preparation of the reactants with defined initial velocities and quantum states in number densities high enough to achieve an acceptable count rate is most important. At the same time, secondary collisions have to be prevented in order to ensure that the nascent products are not thermalized. Usually, the best way to control the initial conditions is to use crossed molecular beams, but the number density decreases quadratically with the distance from the nozzle orifice which can be a problem, especially if a molecular product with a large number of populated states is to be analyzed state specifically by REMPI spectroscopy. In this contribution we would like to present a method for measuring the quantum state selective differential cross section of a photoinitiated reaction that combines the advantages of the PHOTOLOC technique (high reactant densities) and the parallel beams technique used by the groups of Kitsopoulos, Orr-Ewing, and Suits (defined relative velocity of the reactants). Moreover, an algorithm based on a Bayesian backward reconstruction developed by W. H. Richardson [J. Opt. Soc. Am. 62, 55 (1972)] has been derived. Both, one reactant and the precursor of the other reactant, are present in the same molecular beam and the center of mass velocity is selected by shifting the dissociation and the detection laser in time and space. Like in comparable methods, this produces a bias in the measured velocity distribution due to the fact that the reaction takes place in the whole volume surrounding the laser beams. This has been also reported by Toomes et al. in the case of the parallel beams technique and presents a general problem of probing reaction products by REMPI spectroscopy. To account for this, we develop a general approach that can be easily adapted to other conditions. The bias is removed in addition to deconvolution from the spread in reactant velocities. Using the benchmark system O((1)D)+D(2) with N(2)O as the precursor, we demonstrate that the technique is also applicable in a very general sense (i.e., also with a large spread in reactant velocities, products much faster than reactants) and therefore can be used also if such unfortunate conditions cannot be avoided. Since the resulting distribution of velocities in the laboratory frame is not cylindrically symmetric, three dimensional velocity mapping is the method of choice for the detection of the ionized products. For the reconstruction, the distance between the two laser beams is an important parameter. We have measured this distance using the photodissociation of HBr at 193 nm, detecting the H atoms near 243 nm. The collision energy resulting from the 193 nm photodissociation of N(2)O is 5.2+/-1.9 kcal/mol. Our results show a preference for backward scattered D atoms with the OH partner fragment in the high vibrational states (v=4-6), in accord with previously published results claiming the growing importance of a linear abstraction mechanism for collision energies higher than 2.4 kcal/mol.

Three-dimensional velocity map imaging: setup and resolution improvement compared to three-dimensional ion imaging.

For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H(+) ions emerging from the photodissociation of HCl following the two photon excitation to the V (1)Sigma(+) state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Delta v/v = 0.022 compared to 0.086 at v approximately = 17,000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.

Intermediate state polarization in multiphoton ionization of HCl.

The paper presents the detailed theoretical description of the intermediate state polarization and photofragment angular distribution in resonance enhanced multiphoton ionization (REMPI) of molecules and the experimental investigation of these effects in the E(1)Sigma(+) and V(1)Sigma(+) states of HCl populated by two-photon transitions. It is shown that the intermediate state polarization can be characterized by the universal parameter b which is in general a complex number containing information about the symmetry of the two-photon excitation and possible phase shifts. The photofragment angular distribution produced by one- or multiphoton excitation of the polarized intermediate state is presented as a product of the intermediate state axis spatial distribution and the angular distribution of the photofragments from an unpolarized intermediate state. Experiments have been carried out by two complementary methods: REMPI absorption spectroscopy of rotationally resolved (E,v'=0<--X,v"=0) and (V,v'=12<--X,v"=0) transitions and REMPI via the Q(0) and Q(1) rotational transitions followed by three-dimensional ion imaging detection. The values of the parameter b determined from experiment manifest the mostly perpendicular nature of the initial two-photon transition. The experimentally obtained H(+) -ion fragment angular distributions produced via the Q(1) rotational transition show good agreement with theoretical prediction.

Photoionization and photodissociation of HCl(B 1Sigma+, J=0) near 236 and 239 nm using three-dimensional ion imaging.

The electronically excited states HCl(*)(E,upsilon(')=0,J(')=0) and HCl(*)(V,upsilon(')=12,J(')=0) have been prepared by two-photon resonant absorption of ground state HCl via Q(0) transitions at 238.719 and at 236.000 nm, respectively. The consequent one-or two-photon excitation at the same wavelength results in the production of H(+), Cl(+), and HCl(+) ions. The speed distributions and anisotropy parameters beta for these ions have been determined by three-dimensional photo-fragment ion imaging based on a position-sensitive delay-line anode assembly. Several results are presented: first, we measured velocity (speed and angle) distributions for HCl(+) due to the electron recoil in the photoionization of HCl(*). Such distributions give information on the photoionization process and on the vibrational distribution of HCl(+) after the laser pulse. Second, the measured beta parameters for Cl(+) and H(+) distributions give information on the symmetries of the upper states in the one-photon photoexcitation of HCl(*). Third, the measured speed distributions for H(+) help to understand the mechanism of the photodissociation of HCl(+) ions.

A system to reproduce human breathing patterns: its development and validation.

Studies of aerosol deposition in models of the human respiratory tract play a significant role in developing our understanding of drug delivery by inhalation and particle retention in the lungs during exposure to polluted environments. To use replica casts of human airways and compare the results with in vivo data, a device is required to simulate human breathing. The objective of this study was to simulate human breathing for nasal casts. Breathing through the nose is normally limited to about 50 L/min. Therefore, a system was built to simulate human breathing patterns as well as artificial ones up to this flow rate. The system consists of a reciprocating piston in a cylinder, which is displaced by a synchronous motor via a linear actuator. The desired signal to drive the motor is given in real time by purpose-written software. The rotation and position of the motor are controlled by an electronic position control unit. The validation of the system shows that it simulates breathing up to 50 L/min closely even for complex waveforms. At breathing rates above 50 L/min, a slight difference is apparent between the desired breathing pattern and the simulated one. The breathing simulator has been shown to be a reliable tool for reproducing a wide variety of breathing patterns.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. I. Screening strategy and validation.

Chemical screening using thin-layer chromatography and various staining reagents offers the opportunity to visualize an almost complete picture of a microbial secondary metabolite pattern (metabolic finger-print). A thorough application of this strategy resulted in a number of biologically active new secondary metabolites, although the screening strategy is per se not correlated to any biological activity. In the present paper we report on a novel approach called biomolecular-chemical screening which combines the chemical screening strategy with binding studies of biological relevance. Making use of thin-layer chromatography (TLC) and subsequent staining, biomolecular-chemical screening allows to examine binding properties of low molecular weight metabolites to certain bio-macromolecules. The screening strategy itself, as well as independent validation of the results using DNA as selected bio-macromolecule are presented. The biomolecular-chemical screening method is useful to screen binding behaviour towards DNA of both, pure metabolites by one-dimensional TLC, and crude extracts by two-dimensional TLC. Investigation of pure secondary metabolites as well as screening of crude microbial extracts and new secondary metabolites obtained with this screening strategy are presented in accompanying papers.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. II. Application studies with pure metabolites.

The novel screening strategy called "biomolecular-chemical screening" combines the advantages of the chemical screening approach--the analysis of the chromatographic and chemical behaviour of secondary metabolites on TLC plates--with binding studies of these molecules with bio-macromolecules like DNA. This approach was advantageously used to detect the interaction of pure compounds with DNA. In order to prove the reliability of the biomolecular-chemical screening and to examine DNA-binding properties, 470 pure secondary metabolites were analysed by this method. Besides the confirmation of already known binders with the TLC-based method, for a number of natural products DNA-binding properties were discovered for the first time. In consequence, binding of pure compounds can be measured by 1D TLC in a reliable and easy manner, in which DNA is applied together with the test compound at the starting spot. Analysis is performed via differences in Rf-values in comparison to a reference chromatogram without DNA.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. III. New DNA-binding metabolites.

Based on the chemical screening technique, biomolecular-chemical screening has been developed which makes use of two-dimensional TLC analysis of microbial extracts and combines thin-layer chromatography (RP-18) with binding studies towards DNA. In the first dimension the metabolites of the crude microbial extract are separated, and in the second dimension binding properties towards DNA are analysed. An initial screening program with 500 microbial extracts prepared by solid-phase extraction with XAD-16 resin resulted in 17 samples which contained metabolites with significant DNA-binding behavior. Fermentation, isolation and structural characterization led to already known metabolites [phenazine-1,6-dicarboxylate (1), phencomycin (2), 11-carboxy-menoxymycin B (3), soyasaponine I (4), and (8S)-3-(2-hydroxypropyl)-cyclohexanone (5)], as well as to new secondary metabolites. Fermentation of the producing organisms of the new DNA-binding metabolites, ent-8,8adihydro-ramulosin (6). (2R,4R)-4-hydroxy-2-(1,3-pentadienyl)-piperidine (7), (5R)-dihydro-5-pentyl-4'-methyl-4'-hydroxy-2(3H)-furanone (8), and seco-4,23-hydroxyoleane-12-en-22-one-3-carboxylic acid (9), as well as isolation, structural characterization, and physico-chemical properties are reported.

Label-free monitoring of DNA-ligand interactions.

We report on the label- and isotope-free monitoring of DNA interactions with low-molecular-weight ligands. An optical technique based on interference at thin layers was used to monitor in real time binding of ligands at DNA which was immobilized by Coulomb interactions at a positively charged surface. Approximately 2 ng DNA/m2 was irreversibly bound to the surface, which remained stable over several days. This result was confirmed by characterization of the layer using spectroscopic ellipsometry. During incubation of immobilized DNA with a variety of intercalators and other DNA-binding compounds in a flow system, interactions were monitored by reflectometric interference spectroscopy. Binding effects between 10 and 400 pg/ mm2 were detected unambiguously. Nonspecific binding effects were excluded by using a negatively charged reference surface. Variation of intercalator concentration allowed the characterization of interaction with respect to kinetics and thermodynamics by the evaluation of binding rate and equilibrium coverage. The affinity constants were determined in the range between 10(5) and 10(6) M-1, in good agreement to those obtained by homogeneous phase assays. Association rate constants between 10(3) and 10(5) M-1 s-1 and dissociation rate constants between 10(-1) and 10(-2) s-1 were determined by evaluation of the binding curves. Both the fast and simple test format and a universal applicability make the new technique described attractive for detecting and characterizing interaction of low-molecular-weight molecules with DNA.

Specific binding of low molecular weight ligands with direct optical detection.

The characterization of low molecular weight ligand interaction with receptor molecules is of importance for the investigation of biological processes and for drug research. We report on the investigation of the binding of low molecular weight ligands to immobilized receptors by label-free detection. Reflectometric interference spectroscopy, an optical transducer which allows the monitoring of a few picograms per square millimetre changes in surface coverage, was used to study two model systems. In both cases detection of the binding event was successful. High affinity binding of biotin to immobilized streptavidin was clearly detectable at receptor surface concentrations as low as 1-2 x 10(10) binding sites/mm2. Linear correlation between the receptor surface concentration and the response to biotin binding was observed. Using immobilized DNA, we investigated the binding of common intercalators with respect to kinetics and thermodynamics by evaluation of the association and the dissociation part of the binding curve. Bi-exponential increase and decrease of intercalator loading was observed, indicating complex interaction kinetics. The four structurally different intercalators showed significant distinction in binding kinetics and equilibrium signals. Improvement of experimental parameters is required to obtain more reliable kinetic data.

Referee analysis of precious metal sweeps and related materials.

Sweeps samples are often complex mixtures containing from trace amounts to 20% of one or more precious metals distributed in matrices consisting of widely varying mixtures of base metals or their oxides. Three collection procedures are described that are suitable for the isolation of precious metals from base substances. One is based on direct fusion of the sample (high-grade sweeps) with sodium peroxide, and the others on collection of the precious metals by fire-assay techniques using either nickel sulphide or silver. The precious metals are then determined either gravimetrically or by atomic-absorption or plasma-emission spectrometry.