No abstract

The effect of impurity coimplantation in MeV erbium-implanted silicon is studied. A significant increase in the intensity of the 1.54-μm Er3+ emission was observed for different coimplants. This study shows that the Er3+ emission is observed if erbium can form an impurity complex in silicon. The influence of these impurities on the Er3+ photoluminescence spectrum is demonstrated. Furthermore we show the first room-temperature photoluminescence spectrum of erbium in crystalline silicon.

Spectra and optical constants of nitrile ices known or suspected to be in Titan's atmosphere are presented from 2.0 to 333.3 μm (∼5000-30 cm −1 ). These results are relevant to the ongoing modeling of Cassini CIRS observations of Titan's winter pole. Ices studied are: HCN, hydrogen cyanide; C 2 N 2 , cyanogen; CH 3 CN, acetonitrile; C 2 H 5 CN, propionitrile; and HC 3 N, cyanoacetylene. For each of these molecules, we also report new cryogenic measurements of the real refractive index, n, determined in both the amorphous and crystalline phases at 670 nm. These new values have been incorporated into our optical constant calculations. Spectra were measured and optical constants were calculated for each nitrile at a variety of temperatures, including, but not limited to, 20, 35, 50, 75, 95, and 110 K, in both the amorphous phase and the crystalline phase. This laboratory effort used a dedicated FTIR spectrometer to record transmission spectra of thin-film ice samples. Laser interference was used to measure film thickness during condensation onto a transparent cold window attached to the tail section of a closed-cycle helium cryostat. Optical constants, real (n) and imaginary (k) refractive indices, were determined using Kramers-Kronig analysis. Our calculation reproduces the complete spectrum, including all interference effects.

Here we report recent measurements on acetylene (C 2 H 2 ) ices at temperatures applicable to the outer Solar System and the interstellar medium. New near-and mid-infrared data, including optical constants (n, k), absorption coefficients (a), and absolute band strengths (A), are presented for both amorphous and crystalline phases of C 2 H 2 that exist below 70 K. Comparisons are made to earlier work. Electronic versions of the data are made available, as is a computer routine to use our reported n and k values to simulate the observed IR spectra. Suggestions are given for the use of the data and a comparison to a spectrum of Makemake is made.

Extensive experimental studies have been performed on the solid-state formation of the OCS molecule in protonirradiated water-free and water-dominated ices containing CO or CO 2 as the carbon source and H 2 S or SO 2 as the sulfur source. In each case OCS is readily formed. Production efficiency follows the trends CO > CO 2 and H 2 S > SO 2 as C,O-and S-sources, respectively. In water-dominated ices, OCS production appears to be enhanced for CO : H 2 S reactants. The mechanism of formation of OCS appears to be the reaction of CO with free S atoms produced by fragmentation of the sulfur parent species. While OCS is readily formed by irradiation, it is also the most easily destroyed on continued exposure. In H 2 O-dominated ices the half-life of H 2 S, SO 2 , and OCS is $2 eV molecule À1 , corresponding to $7 million years in a cold dense interstellar cloud environment processed by cosmic-ray protons. The spectral profile of the 3 band of OCS is highly dependent on temperature and ice composition, and changes with radiation processing. These effects can be used in theoretical modeling of interstellar infrared (IR) spectra; a laboratory spectrum of irradiated H 2 O : CO : H 2 S, warmed to 50 K, provides a good fit to the 2040 cm À1 feature in the W33A spectrum. The identification of OCS in CO 2-dominated ices provides a further challenge, due to the overlap of the OCS band with that of CO 3 formed from irradiation of the host ice. The two features can be unraveled by a curve-fitting procedure. It is the width of the 2040 cm À1 band that will help observers determine if features identified in CO 2-rich ices are due to OCS or to CO 3 .

No abstract

No abstract

Electron-spin-resonance (ESR) signals attributed to the linear C6, C8, and C10 molecules in their lowest 3Σ states, presumably their ground states, have been observed in solid neon and argon matrices at 4 K. There is evidence of two forms of the C10 molecule, perhaps indicating two slightly bent structural isomers. Laser vaporization of graphite and 13C-enriched graphite produced a high proportion of these larger molecules. Hyperfine interaction in the 13Cn molecules was small and resolved only for C6, indicating cumulene-type bonding with the unpaired spins in pπ orbitals, as in C4. The zero-field-splitting parameters ‖D‖ were found to be 0.363, 0.783, and 0.190 cm−1, respectively, in solid neon. The increase in ‖D‖ through C8 is attributed to a corresponding variation in the spin–orbit coupling with low-lying states, principally the 1Σ+g, as the chains lengthen. Gross orbital spin populations and 1Σ+g– X 3Σ−g energy differences were obtained from Hartree–Fock calculations in order to interpret the hfs and ‖D‖ data, respectively. Electron correlation was included via second and third order Mo/ller–Plesset perturbation theory. The possibility of quasilinear or nonlinear character in these chains is briefly considered. Relative concentrations of the linear and cyclic forms of these molecules in the vapor and in matrices were estimated from thermodynamics using their theoretically derived properties.