The vibrational predissociation spectra of the H5O2 +RGn(RG = Ar,Ne) clusters: correlation of the solvent perturbations in the free OH and shared proton transitions of the Zundel ion

Predissociation spectra of the H(5)O(2) (+)RG(n)(RG = Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm(-1)) and shared proton (850-1950 cm(-1)) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H(5)O(2) (+) [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H(5)O(2) (+) "Zundel" ion remains largely intact in H(5)O(2) (+)Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H(5)O(2) (+)Ar, and is dominated by two sharp transitions at 928 and 1047 cm(-1), with a weaker feature at 1763 cm(-1). The H(5)O(2) (+)Ar(n),n = 1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H(5)O(2) (+) rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H(5)O(2) (+). These results are consistent with assignment of the strong low-energy bands in the H(5)O(2) (+)Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm(-1) band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules.     

The vibrational spectra and rotational isomerism of monochloromethyl acetate and methyl oxalyl chloride

The IR spectra of monochloromethyl acetate and methyl oxalyl chloride have been studied for the vapour, liquid and solid states. For the first ester only one conformation is present and it has a planar arrangement of heavy atoms with the chlorine directed away from the carbonyl group and with a s-cis arrangement for the basic ester framework. For methyl oxalyl chloride, evidence is presented for the presence of two rotamers, the more stable of which is probably planar with a trans arrangement of carbonyl groups.     

A chaos hypothesis for some large systems of random equations

Summary This paper is about the behavior of solutions to large systems of linear algebraic and differential equations when the coefficients are random variables. We will prove a law of large numbers and a central limit theorem for the solutions of certain algebraic systems, and the weak convergence to a Gaussian process for the solution of a system of differential equations. Some of the results were surprisingly difficult to prove, but they are all easily anticipated from a chaos hypothesis: i.e. an assumption of near independence for the components of the solutions of large systems of weakly coupled equations.Supported by the National Science Foundation under grant MCS76-80762, by the U.S. Air Force under grant AFOSR 78-3514 and the U.S. Army under grant DAAG 2980-K-0006     

Head-to-head coiled arrangement of the subunits of the animal fatty acid synthase

The role of the beta-ketoacyl synthase domains in dimerization of the 2505 residue subunits of the multifunctional animal FAS has been evaluated by a combination of crosslinking and characterization of several truncated forms of the protein. Polypeptides containing only the N-terminal 971 residues can form dimers, but polypeptides lacking only the N-terminal 422 residue beta-ketoacyl synthase domain cannot. FAS subunits can be crosslinked with spacer lengths as short as 6 A, via cysteine residues engineered near the N terminus of the full-length polypeptides. The proximity of the N-terminal beta-ketoacyl synthase domains and their essential role in dimerization is consistent with a revised model for the FAS in which a head-to-head arrangement of two coiled subunits facilitates functional interactions between the dimeric beta-ketoacyl synthase and the acyl carrier protein domains of either subunit.     

Synthesis and coordination chemistry of perfluoroalkylated dithiophosphate ligands

Dithiophosphoric acids [HS₂P(OC₂H₄C_nF_2n+1)₂] (n = 4, 6) have been prepared in high yields. Deprotonation and reaction with transition metal substrates affords fluorous metal complexes which have been characterised by elemental analysis, mass spectrometry, IR and NMR spectroscopies. The structures of [Cu{S₂P(OC₂H₄C_nF_2n+1)₂}(PPh₃)₂] (n = 4, 6) and [Cu{-S₂P(OC₂H₄C₄F₉)₂}(PPh₃)]₂ have been determined by single crystal X-ray diffraction.     

A new configuration for coupling purge-and-trap/cryogenic focusing/capillary column gas chromatography with splitless injection mode

A new configuration for coupling a purge-and-trap unit to a capillary column gas chromatograph via a cryogenic focusing interface has been developed. In this configuration, the precolumn of the cryogenic focusing interface was inserted through the septum of a split/splitless injection port where it served as both sample transfer and carrier gas supply lines. The injection port of the gas chromatograph was modified by plugging the carrier gas and the septum purge lines. This configuration allowed for the desorption of analytes at high flow rates while maintaining low, analytical-column flow rates which are necessary for optimum capillary column operation. The capillary column flow rate is still controlled by the column backpressure regulator. Chromatograms of purgeable aromatics exhibited improved resolution, especially for early eluting components compared to those obtained by direct liquid injection using the normal splitless injection mode. Quantitative sample transfer to the analytical column afforded excellent linearity and reproducibility of compounds studied.     

Chelating diphos ligands with inorganic backbones. Crystal structure of [PtCl2{(PPh2O)2SiPh2}]

The metallo-phosphaalkenes (η⁵-C₅Me₅)(CO)₂FeP=C(R)(SiMe₃) (Ia: R = SiMe₃, Ib: R = Ph) and MeO₂C---CC---CO₂Me undergo a dipolar [3+2]-cycloaddition to afford the metallo-heterocycles [(η⁵-C₅Me₅)(CO)

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=C(R)SiMe₃] (IIIa,b) with exocyclic P=C double bonds.     

Thermochemistry of polyhalides. II. Caesium and rubidium dibromoiodides

Using a solution-reaction calorimeter the standard enthalpies of formation of crystalline caesium and rubidium dibromoiodides have been determined as ?445.5±4.1 and ?428.3±4.2 kJ mol^?1, respectively. Thermodynamic parameters, including lattice energies, are calculated and the thermal stability of polyhalides discussed. Thermometric titrations have been used to investigate the mechanism of reaction of caesium dibromoiodide with aqueous silver nitrate.     

Antiresonances in the Rydberg spectrum of naphthalene. A new analysis

The Rydberg “antiresonances” in the spectra of large molecules are reexamined under the assumption that Rydberg level-valence vibronic level mixing is of primary importance in determining the interference phenomenon. The line shape calculated using this point of view fits very well the observed “antiresonance” line shape in the naphthalene spectrum. The formalism also provides a satisfying rationalization for the absence of antiresonances in the Rydberg spectra of most large molecules.