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Experimental and theoretical studies of a novel family of germanium–carbon clusters (Ge[sub n]C[sub m]) that were initiated with our earlier identification of the GeC[sub 3]Ge cluster have now been extended to the GeC[sub 7] and GeC[sub 9] chains. The new clusters, which were formed by laser ablation and trapped in solid Ar at ∼10 K, have been identified using Fourier-transform infrared (FTIR) measurements coupled with density-functional theory (DFT) calculations. The ν[sub 1](σ) vibrational fundamental of linear GeC[sub 7] has been identified at 2063.6 cm-1, and an absorption at 1928.3 cm-1 has been assigned to the ν[sub 4](σ) fundamental of linear GeC[sub 9]. FTIR measurements of the isotopic shifts for the assignments are in good agreement with the DFT predictions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The first optical observation of a mixed germanium-silicon-carbon (Ge[sub l]Si[sub m]C[sub n]) cluster has been made by trapping the products of the laser ablation of carbon/silicon/germanium rods in Ar at 10 K. The ν[sub 1](σ) C-C stretching mode of linear GeC[sub 3]Si has been identified at 1939.0 cm[sup -1]. The assignment is confirmed by the very good agreement between Fourier transform infrared (FTIR) measurements of frequencies and isotopic shifts and predictions of our quantum theoretical calculations. [ABSTRACT FROM AUTHOR]

The ion–molecule complex, Mg+–N2 is formed in a supersonic expansion and studied with mass-selected photodissociation spectroscopy. The lowest energy bands observed in the electronic excitation spectrum are redshifted more than 12 000 cm-1 from the Mg+ (2P←2S) atomic transition at 280 nm. The red-shift, resulting from differential bonding in the ground and excited states of the complex, is much larger than the shifts observed in previously studied Mg+–ligand complexes. Resolved vibronic structure is observed extending for more than 5000 cm-1. The observation of spin–orbit multiplet structure indicates that the complex is linear and that the electronic transition is 2Π←X 2Σ+. The spin–orbit splitting of 46 cm-1 is significantly less than that observed for other Mg+–L complexes. Vibronic intervals of about 1000 and 500 cm-1 are assigned respectively to a stretching mode and to double quanta in a bending mode. The study of isotopically substituted complexes indicates that the best assignment for the stretch progression is the N–N mode, with a frequency far below that in free N2. The vibrational activity, frequency shift, and spin–orbit splitting are all signatures for N2 activation by the excited metal ion. However, the degree of this interaction is greater than that predicted by ab initio calculations. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

AlAg is produced in a supersonic molecular beam by laser vaporization of alloy samples in a pulsed nozzle cluster source. Electronic spectroscopy is studied with resonant two-photon photoionization. In addition to the two electronic excited states previously reported by Clements and Barrow, we have observed ten new states. Vibrational analyses are presented for each of these states, and rotational analyses are given for selected states. The number and characteristics of these excited states are compared to the predictions of recent ab initio calculations. [ABSTRACT FROM AUTHOR]

Mg+–CO2 ion–molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass-selected photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. Two excited electronic states are observed (2) 2Σ+ and 2Π. The 2Π state has a vibrational progression in the metal–CO2 stretching mode (ωe’=381.8 cm-1). The complexes are linear (Mg+–OCO) and are bound by the charge–quadrupole interaction. The dissociation energy (D0‘) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co-workers. [ABSTRACT FROM AUTHOR]

Mg+–H2O ion–molecule complexes are produced in a pulsed supersonic nozzle cluster source. These complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as 2B2←X 2A1 is observed with an origin at 28 396 cm-1. The spectrum has a prominent progression in the metal-H2O stretching mode with a frequency (ω’e) of 518.0 cm-1. An extrapolation of this progression fixes the excited state dissociation energy (D’0) at 15 787 cm-1. The corresponding ground state value (D‘0) is 8514 cm-1 (24.3 kcal/mol). The solvated bending mode, and symmetric and asymmetric stretching modes of water are also active in the complex, as are the magnesium bending modes. A second electronic transition assigned as 2B1←X 2A1 is observed with an origin at 30 267 cm-1 and a metal stretch frequency for Mg+–H2O of 488.5 cm-1 (ΔG1/2). Spectra of both excited states are also observed for Mg+–D2O. Partially resolved rotational structure is analyzed for both isotopes, leading to the conclusion that the complex has a structure with C2v symmetry. This study was guided by ab initio calculations by Bauschlicher and co-workers, which provide accurate predictions of the electronic transition energies, vibrational constants, and dissociation energies. [ABSTRACT FROM AUTHOR]

Vibrationally resolved electronic spectra are reported for the metal dimer-rare gas complexes Ag2–Ar and Ag2–Kr. These spectra are obtained using resonant two-photon photoionization in the energy region near the Ag2 B←X electronic transition (280–285 nm). Both complexes exhibit extensive activity in three vibrational modes, making it possible to determine vibrational constants, anharmonicities, and cross-mode couplings. An unusual cancellation of factors results in the Kr complex (ω’e =72.6 cm-1) having nearly the same metal-rare gas stretching frequency as the Ar complex (ωe=73.9 cm-1). Progressions extending over a significant range of the excited state potential surfaces make it possible to derive the excited state dissociation energies (D’0=755 and 1205 cm-1 for Ar and Kr, respectively). Combination with the red-shifted electronic state origins yields the corresponding ground state dissociation energies (D[larger_closed_square]0=275 and 394 cm-1 for Ar and Kr, respectively). Potential energy surfaces are investigated for excited and ground states of both complexes. [ABSTRACT FROM AUTHOR]

IgM rheumatoid factors capable of complement fixation and activation are commonly present in the sera of adults with rheumatoid arthritis. Hidden complement fixing IgM rheumatoid factor has been demonstrated in the majority of patients with juvenile RA and hidden agglutinating IgM rheumatoid factors have been demonstrated in the serum of adults with seronegative rheumatoid arthritis. We studied 27 adults with seronegative rheumatoid arthritis and were unable to demonstrate hidden complement fixing IgM rheumatoid factor in their sera. [ABSTRACT FROM AUTHOR]

A compact high-resolution (λ/Δλ≈10 000) spherically bent crystal spectrometer in the Johann geometry was recently installed and tested on the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. The curvature of the mica (002) crystal grating allows for higher collection efficiency compared to the flat and cylindrically bent crystal spectrometers commonly used on the Livermore electron beam ion traps. The spectrometer’s Johann configuration enables orientation of its dispersion plane to be parallel to the electron beam propagation. Used in concert with a crystal spectrometer, whose dispersion plane is perpendicular to the electron beam propagation, the polarization of x-ray emission lines can be measured. [ABSTRACT FROM AUTHOR]

The first germanium-carbon cluster GeC[sub 3]Ge, has been detected in the products from the laser evaporation of carbon and germanium rods trapped in solid Ar at ∼10 K. On the basis of very good agreement between Fourier transform infrared (FTIR) measurements and the predictions of density functional theory (DFT) calculations for the frequencies and [sup 13]C isotopic shifts, the ν[sub 3](σ[sub u]) mode of linear GeC[sub 3]Ge has been identified at 1920.7 cm-1. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]