VUV Fourier Transform Spectrometer Research Articles

Direct measurements of electronic ground state ro-vibrationally excited D2 molecules produced on ECR plasma-facing materials by means of VUV-FT absorption spectroscopy

Ro-vibrationally excited molecules of deuterium are involved in non-equilibrium chemical reactions in divertor region of tokamak (see molecular assisted recombination) or in neutral beam injector to produce negative ion (see dissociative electron attachment) for fusion plasmas. These molecules produced both in a plasma volume and on surfaces are no longer in their electronic ground state X1∑g+(v”⩾0,J”) and populate non-uniformly different vibrational (v″) and rotational levels (J″). The high resolution VUV Fourier Transform spectrometer of the DESIRS beam line (SOLEIL synchrotron) is applied to directly scrutinize the ro-vibrationally excited levels of the D2 ground state from v″ = 0 to 10 and J″ up to 8 in an electron cyclotron resonance (ECR) cold plasma. This is performed for different plasma-facing materials, i.e. quartz, tantalum, tungsten, and stainless steel, in order to compare their relative impact in molecular excitation through recombinative desorption from surfaces. A significant effect of these materials on the absolute distribution of the vibrationally states has been found above v″ > 3. The experimental detection limit for Quartz is v″ = 7 whereas tungsten and stainlees steel excite the molecules up to v″ = 9 and tantalum up to v″ = 10. The use of a bare, temperature-controlled surface of Quartz as a reference, compared to metallic surfaces, allows us to determine the relative production of these excited levels. The recombinative desorption rate on tungsten and stainless steel compared to quartz is ~ 2.6 higher and reaches ~ 5 for tantalum.

High-Resolution Study of 13C16O A–X(v′ = 0–9) Bands Using the VUV-FTS at SOLEIL: Revised Term Values

We present high-resolution absorption spectral measurements of the A(1)Π-X(1)Σ(+) band system of (13)C(16)O. These were recorded with the VUV Fourier transform spectrometer (VUV-FTS) installed on the DESIRS beamline at the SOLEIL synchrotron. This work includes revised term values that extend to higher J' values than previous measurements for most v' levels and lower J' values for v' = 0. We confirm previously observed perturbations of the rotational levels in greater detail and present evidence for new perturbations. The accuracy in the wavelength determination and term values is on average within 0.01 cm(-1), improving upon previous measurements.

DESIRS : a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator-based VUV beamline at SOLEIL (France) optimized for the study of gas phase matter in the 5-40 eV range. It is equipped with two dedicated endstations: a VUV Fourier-Transform Spectrometer (FTS) for ultra-high resolution absorption spectroscopy (resolving power up to 106) and an electron/ion imaging coincidence spectrometer. The photon source is a 10 m-long pure electromagnetic variable polarization undulator providing, at the sample location, fully calibrated quasi-perfect horizontal, vertical and circular polarizations. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator higher harmonics. The 6.65 m Eagle off-plane Normal Incidence Monochromator equipped with four gratings allows the tuning of the flux-to-resolution trade-off. Measured ultimate instrumental resolving powers are 124000 (174 μeV) around 21 eV and 250000 (54 μeV) around 13 eV, while the typical measured flux is in the 1010−1011 ph/sec range in a 1/50000 bandwidth and 1012-1013 ph/sec in a 1/1000 bandwidth.

VUV Fourier-transform absorption study of the Lyman and Werner bands in D2

An extensive survey of the D(2) absorption spectrum has been performed with the high-resolution VUV Fourier-transform spectrometer employing synchrotron radiation. The frequency range of 90,000-119,000 cm(-1) covers the full depth of the potential wells of the B (1)Σ(u)(+), B' (1)Σ(u)(+), and C (1)Π(u) electronic states up to the D(1s) + D(2l) dissociation limit. Improved level energies of rovibrational levels have been determined up to respectively v = 51, v = 13, and v = 20. Highest resolution is achieved by probing absorption in a molecular gas jet with slit geometry, as well as in a liquid helium cooled static gas cell, resulting in line widths of ≈0.35 cm(-1). Extended calibration methods are employed to extract line positions of D(2) lines at absolute accuracies of 0.03 cm(-1). The D (1)Π(u) and B'' (1)Σ(u)(+) electronic states correlate with the D(1s) + D(3l]) dissociation limit, but support a few vibrational levels below the second dissociation limit, respectively, v = 0-3 and v = 0-1, and are also included in the presented study. The complete set of resulting level energies is the most comprehensive and accurate data set for D(2). The observations are compared with previous studies, both experimental and theoretical.

DESIRS: a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator-based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas-phase studies of molecular and electronic structures, reactivity and polarization-dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier-transform spectrometer (FTS) for ultra-high-resolution absorption spectroscopy (resolving power up to 10(6)) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5-40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m-long pure electromagnetic variable-polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi-perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic-free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre-focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off-plane normal-incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm(-1), allowing the flux-to-resolution trade-off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10(10)-10(11) photons s(-1) range in a 1/50000 bandwidth, and 10(12)-10(13) photons s(-1) in a 1/1000 bandwidth, which is very satisfactory although slightly below optical simulations. All of these features make DESIRS a state-of-the-art VUV beamline for spectroscopy and dichroism open to a broad scientific community.

The presence of Nd and Pr in HgMn stars

Optical region spectra for a number of upper main sequence chemically peculiar (CP) stars have been observed to study singly and doubly ionized praseodymium and neodymium lines. In order to improve existing atomic data of these elements, laboratory measurements have been carried out with the Lund VUV Fourier Transform Spectrometer (FTS). From these measurements wavelengths and hyperne structure (hfs) have been studied for selected Pr ii ,P riii and Nd iii lines of astrophysical interest. Radiative lifetimes for some excited states of Pr ii have been determined with the aid of laser spectroscopy at the Lund Laser Center (LLC) and have been combined with branching fractions measured in the laboratory to calculate gf values for some of the stronger optical lines of Pr ii. With the aid of the derived gf values and laboratory measurements of the hfs, a praseodymium abundance was derived from selected Pr ii lines in the spectrum of the Am star 32 Aqr. This abundance was used to derive astrophysical gf values for selected Pr iii lines in 32 Aqr, and these gf values were used to get a praseodymium abundance for the HgMn star HR 7775. The praseodymium abundance in HR 7775 was then utilized to derive astrophysical gf values for all observable Pr iii lines in this star. The neodymium abundance, derived from unblended lines of Nd ii in HR 7775, has been utilized to establish astrophysical gf values for observed Nd iii lines in the optical region of this star. Selected Pr iii and Nd iii lines have been identied and studied in a number of HgMn stars and three hot Am stars. The praseodymium and neodymium abundance change rapidly from an approximate 1{1.2 dex enhancement for the hot Am stars to 1.5{3 dex enhancement for the cool HgMn stars, indicating a well-dened boundary between the hot Am and HgMn stars in the vicinity of 10 500 K. The enhancement of praseodymium and neodymium in Am and HgMn stars may be explained by diusive processes active in the stellar atmosphere, while the observed discontinuity might be explained by a thin hydrogen convection zone thought to be present for the Am stars, but absent in the HgMn stars. The absence of a convection zone would cause the diused elements to gather higher in the atmosphere of HgMn stars compared to Am stars, and explain the observed increase in abundance.

Atomic Data for the ReiiUV 1 Multiplet and the Rhenium Abundance in the HgMn‐Type Star χ Lupi

We report new laboratory spectroscopic analyses that have been conducted to acquire wavelength and oscillator strength data for lines of the Re II UV 1 multiplet. Wavelengths were determined to a sub-milliangstrom accuracy for the hyperfine and isotopic structure components from laboratory spectra obtained with the Lund VUV Fourier Transform Spectrometer. An absolute atomic transition probability is reported for Re II 2275.253 A, obtained from its upper level lifetime and an experimentally determined branching fraction. The radiative lifetime of the z 7Po2 level was found to be 4.47 ± 0.22 ns by the method of laser-induced fluorescence. With the new atomic data, synthetic spectra were generated to fit a Hubble Space Telescope Goddard High Resolution Spectrograph echelle mode spectrum of the chemically peculiar HgMn-type star χ Lupi. The weakness of the λ2275.253 A feature only allowed for the determination of an upper limit to the rhenium abundance, which was found to be consistent with the meteoritic value. Thus, in χ Lupi, rhenium appears to be several orders of magnitude less abundant than the apparent surficial abundances of the slightly heavier elements Pt, Au, Hg, and Tl.

Diabatic approach to the close-coupling wave packet method in reactive scattering

This article explores a diabatic formulation of electronically adiabatic quantum reactive scattering problems. In particular, a diabatic approach to the close-coupling wave packet method is developed which allows us to perform, efficiently, accurate calculations using natural coordinate systems for both the reactant and product configurations. The efficiency and accuracy of the method are investigated in terms of the size of the basis sets, as well as in terms of the symmetry of the diabatic coupling and demonstrated for a model H+H2 collinear reaction. Extension of the method to three-dimensional problems is discussed.

A 25 mA isotope shift in B I at 2090 A - A possible diagnostic of the cosmic B-11/B-10 ratio?

view Abstract Citations (33) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A 25 M Angstrom Isotope Shift in B i at 2090 Angstrom : A Possible Diagnostic of the Cosmic 11B/ 10B Ratio? Johansson, Sveneric G. ; Litzen, Ulf ; Kasten, Joerg ; Kock, Manfred Abstract We present the first laboratory measurement of the isotope shift in a ground term transition of neutral boron, B I, performed with the VUV-Fourier Transform Spectrometer at Lund. The two diagonal transitions in the UV 2 multiplet of B I at 2090 A have a net isotope shift of 25 mA. This matches a spectral resolution of about 85,000, obtainable with the high-resolution spectrograph GHRS on board the Hubble Space Telescope. The oscillator strength of the strongest line at 2089.6 A is about the same as for the weakest line in the UV 1 multiplet at 2496.8 A, often used in abundance studies of boron. Furthermore, the lines at 2090 A are outside the compact resonance region of singly ionized iron-group elements between 2300 and 2700 A. A preliminary study of a synthetic spectrum in this region indicates that the 2089.6 A line is free from blends of lines from high-abundance elements. We propose the use of the B I lines at 2090 A for studies of the abundance and the cosmic isotope composition of neutral boron to test the theories for boron production by big bang nucleosynthesis and cosmic-ray spallation. Publication: The Astrophysical Journal Pub Date: January 1993 DOI: 10.1086/186713 Bibcode: 1993ApJ...403L..25J Keywords: Astronomical Spectroscopy; Boron Isotopes; Galactic Evolution; Absorption Spectra; Abundance; Cosmic Rays; Hubble Space Telescope; Nuclear Astrophysics; Spectrum Analysis; Astrophysics; ATOMIC DATA; LINE: IDENTIFICATION; GALAXY: EVOLUTION; ULTRAVIOLET: STARS full text sources ADS |