J. J. ter Meulen

Laser-induced fluorescence with tunable excimer lasers as a possible method for instantaneous temperature field measurements at high pressures: checks with an atmospheric flame

A new method for instantaneous temperature field measurements based on LIF studies of OH, O(2), and H(2)O in an open atmospheric flame with a tunable excimer laser is suggested. In this method the crucial problem of quenching at higher pressures is almost completely eliminated by excitation to a fast predissociating state. The various possible excitation and fluorescence processes that can be induced in the narrow tuning range of the KrF laser are characterized experimentally by excitation and dispersion spectra for the three molecules OH, O(2), and H(2)O. Of particular importance is the large power of the KrF laser, which allows efficient excitation of even weak transitions. The fast predissociation of these molecules in connection with the powerful excitation laser suggests that instantaneous temperature field measurements should be possible at higher pressures.

Photoionization spectroscopy of dichromium and dimolybdenum: Ionization potentials and bond energies

Photoionization spectroscopy has been used to probe molecular beams of laser-vaporized chromium (Cr2) and molybdenum (Mo2) dimers. Two-color photoionization efficiency spectroscopy has been used to determine the adiabatic ionization potential (IP) of Cr2 and Mo2 to be 56 449±8 cm−1 and 56 042±8 cm−1, respectively. The IP of Cr2 is combined with the IP of Cr [54 575.6±0.3 cm−1, Huber et al., Proc. R. Soc. London, Ser. A 342, 431 (1975)] and the bond energy of Cr2+ [10 200±500 cm−1, Su et al., Chem. Phys. Lett. 201, 199 (1993)] to yield a bond energy of 12 400±500 cm−1 for Cr2. One-color resonant two-photon ionization (R2PI) spectroscopy has been employed to probe the molybdenum dimer molecule in the energy region where its dissociation should occur. The dissociation limit has been ascribed to the threshold observed at 36 100±80 cm−1. This value is combined with the IP of Mo [57 204.3±0.3 cm−1, Rayner et al., J. Opt. Soc. Am. B 4, 900 (1987)] and Mo2 to yield a bond energy of 37 260±80 cm−1 for Mo2+.

CVD diamond deposition on steel using arc-plated chromium nitride interlayers

This paper reports on hot filament CVD diamond deposition onto steel using arc-plated chromium nitride (CrN) as the interlayer. Direct deposition of diamond onto steel leads to the formation of a non-adhering layer of graphitic soot covered by poor-quality diamond. However, if arc-plated CrN coatings with a thickness of 2.5 μm are used, diamond formation takes place. Adherent and good-quality diamond coatings are obtained after several hours of deposition at a substrate temperature as low as 650 °C. Micro-Raman spectroscopy, scanning electron microscopy, X-ray diffraction and EDAX analysis have been employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers and the modified substrate interlayers. The Scotch tape test is used to assess the adhesion of the diamond coatings.

The submillimeter rotation tunneling spectrum of the water dimer

Rotational tunneling transitions have been measured for the (Ka = 0, lower) → (Ka = 1, upper) and the (Ka = 1, lower) → (Ka = 2, upper) bands of (H2O)2. Although some of these transitions have been reported in an earlier publication, a more detailed discussion of the experiment and of the results is presented here. Transitions have been measured by direct absorption spectroscopy in a continuous slit nozzle expansion using either harmonics from klystrons or sidebands. These data along with previous measurements have been analyzed using an IAM-like treatment. A better determination of the A rotational constant and of the value of the largest tunneling splitting has been achieved.

State-to-state cross sections for rotational excitation of OH by collisions with He and Ar

Parity resolved state‐to‐state cross sections for rotational excitation of OH(X 2Π) colliding with He and Ar, have been obtained in a crossed molecular beam experiment. The OH radicals were produced in a pulsed dc discharge in a H2O/Ar gas mixture. Adiabatic expansion into vacuum resulted in an effective rotational cooling yielding a 94% population of the lowest Λ‐doublet (X 2Π3/2, J=3/2). Further state preparation could be achieved via electrostatic state selection in a hexapole electric field, resulting in a 93.5% population of the upper Λ‐doublet component (f,+). Experiments were performed both with and without the state selector to provide detailed information about the rotational excitation from both Λ‐doublet states. The OH rotational state distribution was probed, before and after the collision event, by means of laser‐induced fluorescence (LIF) spectroscopy of the A←X electronic band at 308 nm. The OH–Ar and OH–He scattering behave very similar with the exception of the J=3/2 Λ‐doublet transition ...

Nitric oxide flow tagging in unseeded air

A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO.

Sensitive quantum state selective detection of H2O and D2O by (2+1)‐resonance enhanced multiphoton ionization

The first observation of (2+1)‐REMPI of H2O and D2O is reported. With the use of a high power tunable excimer laser radiating at 248 nm, the H2O and D2O molecules are ionized after resonant two‐photon absorption into the predissociated C 1B1 state. The clearly observable peaks in the (2+1)‐REMPI spectra are all identified and can be used for sensitive state selective detection. Parent molecular fluorescence excitation spectra (C 1B1→A 1B1) were remeasured over an increased spectral range, and are remarkably the same as the (2+1)‐REMPI spectra. Furthermore the OH/OD (A 2Σ+, v’=0→X 2Π, v‘=0) photofragment fluorescence excitation spectra were measured, and these spectra do not show any nonresonant background as stated before. Additional fluorescence bands starting from the vibrationally excited A 2Σ+, v’=1 state were observed. Simulation of the observed REMPI and fluorescence excitation spectra yields the branching ratios for the predissociation, ionization, and fluorescence processes.

Monitoring neurotransmitter release using surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is a promising tool to monitor neurotransmitter release at the single-cell level: it is a sensitive technique that provides structural information of the released compounds and spatial information about their release sites. In this study we demonstrate that depolarization-evoked catecholamine secretion by rat phaeochromocytoma (PC12) cells can be spatially resolved by SERS using silver colloids. A suitable SERS substrate was created by adding silver colloids to the cell culture medium. Nomarski-DIC microscopy combined with reflection confocal laser scanning microscopy showed that the colloids were primarily present on top of the cell membrane. The SERS spectra were successfully corrected for the contribution of cell constituents. Dopamine and noradrenaline were localized by examining the correlation coefficient between spectra and reference catecholamine spectra. Potential improvements of the temporal resolution of the technique are discussed.

Diffusion-modified boride interlayers for chemical vapour deposition of low-residual-stress diamond films on steel substrates

The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adherent, low-residual-stress diamond films on ferritic tool and AISI type 316 austenitic stainless steels was investigated. The steel samples were borided by means of a pack cementation process at a temperature of 950 8C using an interrupted thermal cycling process. Boriding of the alloy steels results in a very high surface hardness of approximately 3780 VHN due to the precipitation of alloy borides such as chromium boride in the predominantly FeBand yor Fe Bcase. The boriding conditions, and hence the microstructural state of the 2 as-borided steels, was found to have a strong influence on the diamond film characteristics, particularly on the adherence. Detailed characterisation of the as-borided steels, as well as the deposited diamond films and interlayer modification during the CVD process, is discussed based on scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy investigations. Under optimised conditions, adherent and continuous diamond films of good quality have been obtained on both the ferritic tool and austenitic stainless steels. In the case of borided surface structures without the presence of a FeBphase, diffusion-modified gradient microstructures were found to accommodate efficiently the high thermal stress expected between the steel substrate and the diamond film, resulting in low-residual-stress films. 2003 Elsevier Science B.V. All rights reserved.

Rotationally inelastic collisions of OH(X 2Π)+Ar. I. State-to-state cross sections

Inelastic collisions of OH(X 2Π)+Ar at an energy of 746 cm−1 have been studied in a crossed molecular beam experiment. The OH(X 2Π) radicals were prepared in the v=0, Ω=32, J=32, f state by hexapole state selection. Parity-resolved integral state-to-state cross sections for rotational excitation have been determined up to the Ω=32, J=92 and Ω=12, J=52 states. A strong preference is found for spin–orbit manifold conserving transitions to final states of e symmetry. The experimental results are compared to quantum scattering calculations on ab initio potential energy surfaces developed by Degli-Esposti and Werner [J. Chem. Phys. 93, 3351 (1990)] and by Klos et al. [J. Chem. Phys. 112, 4952 (2000)]. The overall agreement between experiment and theory is very good; however, the calculated cross sections for spin–orbit changing transitions are a bit larger than the experimental values. The results are also compared to previous experiments at a collision energy of 451 cm−1.