Small asymmetric and symmetric carbon−sulfur clusters, C
n
S and SC
n
S (n = 1−5), have been generated by
pulsed laser ablation of a carbon/sulfur mixture, deposited in an argon matrix at 12 K, and studied via Fourier
transform infrared absorption spectroscopy. Previous vibrational band assignments for a number of these
clusters have been confirmed and new assignments for others have been made using a combination of isotopic
(12C/13C) substitution and density functional (B3LYP/6-311G*) and ab initio (MP2) theoretical calculations.
Reactions of neutral C
n
(n = 1−9) and C
m
S (m = 6−0) fragments are shown theoretically to be highly
exothermic. Evidence for such aggregation reactions in the formation of the clusters is found from isotopomeric
band intensities. Given their calculated vibrational band intensities and estimated column densities, it is proposed
that the direct observation via IR spectroscopy of C5S and SC5S clusters in the envelope of the carbon star,
IRC+10216, and, possibly, the Taurus molecular cloud, TMC-1, is an attractive possibility.
Lithium and sodium complexes of dimethyl ether (DME) and dimethoxyethane (DXE) were produced by reactions of laser-vaporized metal atoms with organic vapors in a pulsed nozzle cluster source. The mono-ligand complexes were studied by photoionization and pulsed field ionization zero electron kinetic energy (ZEKE) spectroscopy. Vibrationally resolved ZEKE spectra were obtained for Li(DME), Na(DME) and Li(DXE) and a photoionization efficiency spectrum for Na(DXE). The ZEKE spectra were analyzed by comparing with the spectra of other metal-ether complexes and with electronic structure calculations and spectral simulations. Major vibrations measured for the M(DME) (M=Li,Na) ions were M-O and C-O stretches and M-O-C and C-O-C bends. These vibrations and additional O-Li-O and O-C-C-O bends were observed for the Li(DXE) ion. The M(DME) complexes were in C2v symmetry with the metal atom binding to oxygen, whereas Li(DXE) was in a C2 ring configuration with the Li atom attaching to both oxygen atoms. Moreover, the ionization energies of these complexes were measured from the ZEKE or photoionization spectra and bond dissociation energies were derived from a thermodynamic cycle.
Cu-(pyridine)n (n = 1, 2) complexes are prepared in a pulsed laser ablation cluster source and identified using laser photoionization time-of-flight mass spectrometry. High-resolution electron spectra of these complexes are obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Metal-pyridine and pyridine-based vibrational modes are identified by comparing the ZEKE spectra with previous spectroscopic studies of isolated pyridine, pyridine adsorbed on metal surfaces, and other Cu complexes. Ground electronic states and molecular structures are determined by comparing the ZEKE spectra with ab initio and multidimensional Franck-Condon factor calculations. Metal-pyridine bond energies of the neutral complexes are derived from the measured ionization energies and thermochemical relations. The mono-ligand complex has C2v symmetry in both the neutral and ionized forms, whereas the di-ligand complex has an eclipsed pyridine configuration with D2h and C2 symmetries for the ion and neutral species, respectively. Although both the mono- and di-pyridine Cu complexes are formed by Cu binding to nitrogen atoms, important binding differences are found between these two complexes.Key words: pulsed-field ionization, ZEKE, photoelectron, ab initio, copper-pyridine complexes.[Traduit par la Rédaction]
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