J. E. Lawler

Improved Laboratory Transition Parameters forEu II and Application to the Solar Europium Elemental and Isotopic Composition

New radiative lifetime measurements using time-resolved laser-induced fluorescence are reported for the lowest six even-parity levels of Eu II. Branching fractions, measured from Fourier transform spectra, are combined with these lifetimes to determine atomic transition probabilities for the strongest blue-UV lines and additional yellow-red lines of Eu II. These results are compared with published data, and generally good agreement is found. Recommended hyperfine structure constants and isotopic shifts for these lines are also assembled from the literature and supplemented, as needed, using results from nonlinear least-squares fits of line profiles in Fourier transform spectra. These laboratory data are applied in a new determination of the solar Eu elemental abundance, yielding log10 e(Eu) = 0.52 ± 0.01, with ±0.04 estimated for each of internal (scatter) and external (systematic) uncertainties. From analysis of the profiles of three Eu II lines, primarily λ4129, isotopic fractions of 151Eu and 153Eu are shown to be consistent with their values in meteoritic material.

Experimental Radiative Lifetimes, Branching Fractions, and Oscillator Strengths for La II and a New Determination of the Solar Lanthanum Abundance

Radiative lifetimes, accurate in most cases to ±5%, from time-resolved laser-induced fluorescence measurements on a slow beam of lanthanum ions are reported for 31 odd-parity levels of La II. Experimental branching fractions for La II from emission spectra covering the near-ultraviolet to the near-infrared are also reported. The spectra were recorded using the US National Solar Observatory 1.0 m Fourier transform spectrometer. The branching fractions are combined with the radiative lifetimes to produce 84 experimentally determined transition probabilities or oscillator strengths, generally accurate to ±10%, for La II. These new experimental results are compared to older experimental and theoretical results. These data are applied to determine a new value for the solar photospheric lanthanum abundance, (La) = 1.13, with estimated internal errors of ±0.03 and external errors of ±0.03.

Lifetimes, transition probabilities, and level energies in Fe i

We use time-resolved laser-induced fluorescence to measure the lifetime of 186 Fe levels with energies between 25 900 and 60 758 cm . Measured emission branching fractions for these levels yield transition probabilities for 1174 transitions in the range 225-2666 nm. We find another 640 Fe transition probabilities by interpolating level populations in the inductively coupled plasma spectral source. We demonstrate the reliability of the interpolation method by comparing our transition probabilities with absorption oscillator strengths measured by the Oxford group [Blackwell et al., Mon. Not. R. Astron. Soc. 201, 595-602 (1982)]. We derive precise Fe level energies to support the automated method that is used to identify transitions in our spectra.

IMPROVED LABORATORY TRANSITION PROBABILITIES FOR Nd ii AND APPLICATION TO THE NEODYMIUM ABUNDANCES OF THE SUN AND THREE METAL-POOR STARS

Radiative lifetimes, accurate to � 5%, have been measured for 168 odd-parity levels of Nd ii using laser-induced fluorescence. The lifetimes are combined with branching fractions measured using Fouriertransform spectrometry to determine transition probabilities for over 700 lines of Nd ii. This work is the largest-scale laboratory study to date of Nd ii transition probabilities using modern methods. This improved data set is used to determine Nd abundances for the Sun and three metal-poor giant stars with neutroncapture enhancement: CS 22892� 052, HD 115444, and BD +17 � 3248. In all four stars the line-to-line scatter is considerably reduced from earlier published results. The solar photospheric abundance is determined to be log � ðNd Þ¼ 1:45 � 0:01ð� ¼ 0:05Þ, which is in excellent agreement with meteoric data. The ratio of Nd/Eu is virtually identical in all three metal-poor Galactic halo stars. Furthermore, the newly determined stellar Nd abundances, in comparison with other heavy neutron-capture elements, are consistent with an r-process–only origin early in the history of the Galaxy. These more accurate Nd abundance determinations might help to constrain the predicted solar system r-process abundances, and suggest other elements for further neutron-capture abundance studies. Subject headings: atomic data — stars: abundances — Sun: abundances On-line material: machine-readable tables

Absolute transition probabilities in Sc i and Sc ii

Absolute atomic transition probabilities for emission lines from 70 levels in Sc i and Sc ii are reported. The transition probabilities are from emission branching ratios measured using the 1.0-m Fourier-transform spectrometer at the National Solar Observatory. Radiative lifetimes, measured using time-resolved laser-induced fluorescence, provide the normalization for converting the branching ratios to absolute transition probabilities. These results are compared with other experimental and theoretical transition probabilities.

Radiative lifetimes, branching rations, and absolute transition probabilities in Cr II and Zn II

New absolute atomic transition probability measurements are reported for 12 transitions in Cr II and two transitions in Zn II. These transition probabilities are determined by combining branching ratios measured by classical techniques and radiative lifetimes measured by time-resolved laser-induced fluorescence. The measurements are compared with branching fractions, radiative lifetimes, and transition probabilities in the literature. The 206 nm resonance multiplets in Cr II and Zn II are included in this work. These multiplets are very useful in determining the distribution of the elements in the gas versus grain phases in the interstellar medium.

IMPROVED Ti II log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

Atomic transition probability measurements for 364 lines of Ti II in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.

Swan band emission intensity as a function of density

We report the systematic comparison of the optical emission intensity of the vibrational band of the Swan system with the absolute concentration in and microwave plasmas used in the deposition of nanocrystalline diamond. The absolute concentration is obtained using white-light absorption spectroscopy. Emission intensity correlates linearly with density for variations of several plasma parameters and across two decades of species concentration. Although optical emission intensity generally is not an accurate quantitative diagnostic for gas phase species concentrations, these results confirm the reliability of the (0,0) Swan band for relative determination of density with high sensitivity under conditions used for hydrogen-deficient plasma-enhanced chemical vapour deposition of diamond.

Lifetimes, branching ratios, and absolute transition probabilities in Hg i

Radiative lifetimes for ten levels from five configurations of Hg are determined by using time-resolved laser-induced fluorescence on a Hg atomic beam. Branching ratios for UV and visible transitions from the levels are measured by using classical spectrophotometric techniques. A careful assessment of the total strength of IR transitions from the levels is performed by using both experimental and theoretical results. Lifetimes and branching ratios from this experiment are compared with results in the literature and with results from single-configuration calculations. Our experimental lifetimes and branching ratios are combined to determine accurate atomic transition probabilities for 23 lines that are commonly used to diagnose Hg plasmas.

Spectroscopic determination of carbon dimer densities in and plasmas

In contrast to conventional methods of diamond chemical vapour deposition (CVD), nanocrystalline diamond CVD takes place with only a small fraction of feed gas hydrogen. Minimal amounts of , believed critical in hydrogen-rich CVD, are expected to be produced in hydrogen-deficient systems and alternative mechanisms for diamond growth must be considered. The carbon dimer, , is believed to be an important species in these growth environments. We have experimentally determined the density of gas phase in and microwave plasmas used to deposit nanocrystalline diamond. The density is monitored using high-sensitivity absorption spectroscopy of the (0, 0) band as chamber pressure, microwave power, substrate temperature and feed gas mixtures are varied for these two chemical systems. The absolute density of is most sensitive to the total chamber pressure and fraction of carbon in all molecular species in the feed gas in discharges and to the total chamber pressure and substrate temperature in plasmas. We discuss possible production channels in both chemical systems. The efficiency of production from fullerene precursors is over an order of magnitude greater than that from hydrocarbon precursors.