X-Ray Photoabsorption of Density-sensitive Metastable States in Ne VII, Fe XXII, and Fe XXIII

Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify Kα transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 1010.5 cm-3

On the Transition Rate of the Fe X RED Coronal Line

We present a lifetime measurement of the 3s 23p 5 2 Po 1/2 first excited fine-structure level of the ground state configuration in chlorine-like Fe X, which relaxes to the ground state through a magnetic dipole (M1) transition (the so-called red coronal line) with a wavelength accurately determined to 637.454(1) nm. Moreover, the Zeeman splitting of line was observed. The lifetime of 14.2(2) ms is the most precise one measured in the red wavelength region and agrees well with advanced theoretical predictions and an empirically scaled interpolation based on experimental values from the same isoelectronic sequence

X-ray resonant photoexcitation: line widths and energies of K{\alpha} transitions in highly charged Fe ions

Photoabsorption by and fluorescence of the K{\alpha} transitions in highly charged iron ions are essential mechanisms for X-ray radiation transfer in astrophysical environments. We study photoabsorption due to the main K{\alpha} transitions in highly charged iron ions from heliumlike to fluorinelike (Fe 24+...17+) using monochromatic X-rays around 6.6 keV at the PETRA III synchrotron photon source. Natural linewidths were determined with hitherto unattained accuracy. The observed transitions are of particular interest for the understanding of photoexcited plasmas found in X-ray binaries and active galactic nuclei.Comment: Revised versio

High-resolution Photo-excitation Measurements Exacerbate the Long-standing Fe XVII Emission Problem

We measured the L-shell soft X-ray fluorescence of Fe XVII ions in an electron beam ion trap following resonant photo-excitation using synchrotron radiation provided by the P04 beamline at PETRA III. Special attention is paid to two 2p-3d transitions, the 3C and 3D lines that are essential plasma diagnostics tools for astrophysics. Their resulting oscillator-strength ratio, f(3C)/f(3D) = 3.09(8)(6), is three times more accurate than previous results. The present ratio clearly departs by approximately 5-sigmas from the newest ab initio calculations but confirms previous laboratory measurements and astrophysical observations. A ten thousand-fold reduction in excitation-photon intensity and ten times higher spectral resolution allow us to exclude current explanations, reinstating a forty-year-old atomic-physics puzzle

A new benchmark of soft X ray transition energies of Ne, CO2, and SF6 paving a pathway towards ppm accuracy

A key requirement for the correct interpretation of high resolution X ray spectra is that transition energies are known with high accuracy and precision. We investigate the K shell features of Ne, CO2, and SF6 gases, by measuring their photo ion yield spectra at the BESSY II synchrotron facility simultaneously with the 1s np fluorescence emission of He like ions produced in the Polar X EBIT. Accurate ab initio calculations of transitions in these ions provide the basis of the calibration. While the CO2 result agrees well with previous measurements, the SF6 spectrum appears shifted by amp; 8764;0.5 eV, about twice the uncertainty of the earlier results. Our result for Ne shows a large departure from earlier results, but may suffer from larger systematic effects than our other measurements. The molecular spectra agree well with our results of time dependent density functional theory. We find that the statistical uncertainty allows calibrations in the desired range of 1 10 meV, however, systematic contributions still limit the uncertainty to amp; 8764;40 100 meV, mainly due to the temporal stability of the monochromator energy scale. Combining our absolute calibration technique with a relative energy calibration technique such as photoelectron energy spectroscopy will be necessary to realize its full potential of achieving uncertainties as low as 1 10 me

High-Precision Determination of Oxygen K??Transition Energy Excludes Incongruent Motion of Interstellar Oxygen

We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O-2 with 8 meV uncertainty. We reveal a systematic similar to 450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O-2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level

Observation of strong two-electron-one-photon transitions in few-electron ions

We resonantly excite the K series of O5+ and O6+ up to principal quantum number n = 11 with monochromatic x rays, producing K-shell holes, and observe their relaxation by soft-x-ray emission. Some photoabsorption resonances of O5+ reveal strong two-electron-one-photon (TEOP) transitions. We find that for the [(1s2s)(1)5p(3)(/2)](3/2;1/2) states, TEOP relaxation is by far stronger than the radiative decay and competes with the usually much faster Auger decay path. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper states [(1s2p(3)(/2))(1)4s](3/2;1/2) of a Li-like satellite blend of the He-like K alpha transition. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where electronic energy degeneracies are far more common and configuration mixing is stronger

VIBRATIONAL SPECTRA OF ISOTOPIC HALOGEN NITRATES.

Supported by the Air Force Cambridge Research Laboratories and by Public Health Division of Air Pollution.Author Institution: Department of Chemistry, Whitmore Laboratory The Pennsylvania State UniversityThe infrared spectra of fluorine nitrate $(FONO_{2})$ and chlorine nitrate $(ClONO_{2})$, including those of the nitrogen-15 isotopic compounds, have been obtained in the gas and solid phases. The far infrared spectra of the nitrogen-14 compounds in the gas phase were also examined, but only the torsional frequency at $152 cm^{-1}$ of the fluoride was observed. The barrier to internal rotation of the FO-group was calculated to be 10.2 kcal/mole, which is slightly greater than that in nitric acid. The present work showed that previous assignments of the fundamentals of these molecules must be revised, and the new assignments will be discussed

VIBRATIONAL SPECTRA OF ISOTOPIC NITRYL HALIDES.

Supported by the Air Force Cambridge Research Laboratories and by the Public Health Division of Air Pollution.Author Institution: Department of Chemistry, Whitmore Laboratory, The Pennsylvania State UniversityThe infrared spectra of the N-14 and N-15 isotopic species of $NO_{2}Cl$ and $NO_{2}F$ have been investigated in the vapor and solid states. Assignments of two fundamental frequencies in both halides have been changed from those of previous studies. The original assignments of $\nu_{3}$ and $\nu_{5}$ have been reversed in the case of $NO_{2}Cl$ and a band at $460 cm^{-1}$ in $NO_{2}F$ which had been attributed to $\nu_{3}$ was shown to originate from an impurity. New sets of force constants using both the Valence Force Field and the Urey-Bradley Force Field were calculated. $NO_{2}Cl$ was found to be particularly favorable for normal coordinate analysis and unique force constants were determined