Rotational spectra of the van der Waals complexes of molecular hydrogen and OCS

The a- and b-type rotational transitions of the weakly bound complexes formed by molecular hydrogen and OCS, para-H2-OCS, ortho-H2-OCS, HD-OCS, para-D2-OCS, and ortho-D2-OCS, have been measured by Fourier transform microwave spectroscopy. All five species have ground rotational states with total rotational angular momentum J=0, regardless of whether the hydrogen rotational angular momentum is j=0 as in para-H2, ortho-D2, and HD or j=1 as in ortho-H2 and para-D2. This indicates quenching of the hydrogen angular momentum for the ortho-H2 and para-D2 species by the anisotropy of the intermolecular potential. The ground states of these complexes are slightly asymmetric prolate tops, with the hydrogen center of mass located on the side of the OCS, giving a planar T-shaped molecular geometry. The hydrogen spatial distribution is spherical in the three j=0 species, while it is bilobal and oriented nearly parallel to the OCS in the ground state of the two j=1 species. The j=1 species show strong Coriolis coupling with unobserved low-lying excited states. The abundance of para-H2-OCS relative to ortho-H2-OCS increases exponentially with decreasing normal H2 component in H2He gas mixtures, making the observation of para-H2-OCS in the presence of the more strongly bound ortho-H2-OCS dependent on using lower concentrations of H2. The determined rotational constants are A=22 401.889(4) MHz, B=5993.774(2) MHz, and C=4602.038(2) MHz for para-H2-OCS; A=22 942.218(6) MHz, B=5675.156(7) MHz, and C=4542.960(7) MHz for ortho-H2-OCS; A=15 970.010(3) MHz, B=5847.595(1) MHz, and C=4177.699(1) MHz for HD-OCS; A=12 829.2875(9) MHz, B=5671.3573(7) MHz, and C=3846.7041(6) MHz for ortho-D2-OCS; and A=13 046.800(3) MHz, B=5454.612(2) MHz, and C=3834.590(2) MHz for para-D2-OCS.     

Quantitative lateral force microscopy study of the dolomite (104)-water interface

The friction and lateral stiffness of the contact between an atomic force microscopy (AFM) probe tip and an atomically flat dolomite (104) surface were investigated in contact with two aqueous solutions that were in equilibrium and supersaturated with respect to dolomite, respectively. The two aqueous solutions yielded negligible differences in friction at the native dolomite-water interface. However, the growth of a Ca-rich film from the supersaturated solution, revealed by X-ray reflectivity measurements, altered the probe-dolomite contact region sufficiently to observe distinct friction forces on the native dolomite and the film-covered surface regions. Quantitative friction-load relationships demonstrated three physically distinct load regimes for applied loads up to 200 nN. Similar friction forces were observed on both surfaces below 50 nN load and above 100 nN load. The friction forces on the two surfaces diverged at intermediate loads. Quantitative measurements of dynamic friction forces at low load were consistent with the estimated energy necessary to dehydrate the surface ions, whereas differences in mechanical properties of the Ca-rich film and dolomite surfaces were evidently important above 50 nN load. Attempts to fit the quantitative stiffness-load data using a Hertzian contact mechanical model based on bulk material properties yielded physically unrealistic fitting coefficients, suggesting that the interfacial contact region must be explicitly considered in describing the static and dynamic contact mechanics of this and similar systems.     

A dynamic study of earthworm feeding ecology -using stable isotopes

Changes in the specific diet of earthworms with time in relation to landuse changes and two different climates were studied by analysing (13)C and (15)N natural abundance in soils and animals. Soil samples from three depths (0-10, 10-20 and 20-30 cm) and earthworms were collected from two sites: Santiago (Northwest Spain) and North Wyke (Southwest England) both consisting of replicated long-term grasslands and recently converted to maize plots. Earthworms were hand-sorted in the field at the peak of the maize growth and after harvesting at both sites. In the Spanish plots, nine and eight earthworm species, all belonging to the three ecological categories (epigeic, anecic and endogeic), were found under maize and permanent pasture, whereas at the English site five and seven different species were, respectively, identified. At both sites (13)C isotopic values of the earthworm tissues reflected changes in diet from C(3) to C(4) with epigeic and epi/anecic worms in the maize plots showing one delta unit difference in relation to the ones found in the grassland plots. Anecic worms seemed to be less responsive to landuse changes. The higher (13)C values of the Spanish soils were also reflected in the earthworm tissues when compared with the English samples. (15)N values showed no clear relationship with the cropping treatments but were clearly related to the ecological grouping, with endogeic worms reaching the highest values whereas for the epigeic and epi/anecic species the lowest values were obtained. This finding was also previously recorded by other authors1 and suggests that, in the future, stable isotope techniques could also be a useful tool in taxonomic studies. Copyright 1999 John Wiley & Sons, Ltd.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Neutron reflectivity studies of hot polymer melt interfaces

Neutron reflectivity data have been obtained using a specially designed cell that allows the investigation of the interfaces between polymers in the melt state. Systems which are semicrystalline at room temperature can be investigated for the first time. Example results from a polystyrene (PS)/ polyethylene (PE) interface (both with and without copolymer) and an isotactic polypropylene (PP)/ high density polyethylene interface are presented.     

Terthienyl-Based Redox-Switchable Hemilabile Ligands: Transition Metal Polymeric Complexes with Electrochemically Tunable or Switchable Coordination Environments?

By controlling the extent of oxidation of the polymeric forms of the new class of isolable, polymerizable terthienyl Ru^II complexes 1 , one can modulate both the binding strength of the polymer backbone for Ru^II and the electronic nature of the bound metal centers.     

Transgenic peas expressing an α‐amylase inhibitor gene from beans show altered expression and modification of endogenous proteins

Differential in‐gel electrophoresis showed contrasting effects of the transgenic expression of an α‐amylase inhibitor from beans on the proteomes of two pea cultivars. One cultivar showed minor changes relative to its non‐transgenic parent with only one protein changing by more than about twofold. Changes in the abundance of certain endogenous proteins in the other cultivar were of greater number and magnitude with some endogenous proteins undetected while some new protein spots appeared in the transgenic proteome. The sets of proteins with altered expression were generally different between the two cultivars. Some of the proteins that were differentially expressed were identified by MS. Most were seed storage globulins, which are sited together with the transgenic product. Some of the changes may be due to alterations in expression levels but there were also changes due to post‐translational processing.     

Toward exceeding the Shockley-Queisser limit: photoinduced interfacial charge transfer processes that store energy in excess of the equilibrated excited state

Nanocrystalline (anatase), mesoporous TiO2 thin films were functionalized with [Ru(bpy)2(deebq)](PF6)2, [Ru(bq)2(deeb)](PF6)2, [Ru(deebq)2(bpy)](PF6)2, [Ru(bpy)(deebq)(NCS)2], or [Os(bpy)2(deebq)](PF6)2, where bpy is 2,2'-bipyridine, bq is 2,2'-biquinoline, and deeb and deebq are 4,4'-diethylester derivatives. These compounds bind to the nanocrystalline TiO2 films in their carboxylate forms with limiting surface coverages of 8 (+/- 2) x 10(-8) mol/cm2. Electrochemical measurements show that the first reduction of these compounds (-0.70 V vs SCE) occurs prior to TiO2 reduction. Steady state illumination in the presence of the sacrificial electron donor triethylamine leads to the appearance of the reduced sensitizer. The thermally equilibrated metal-to-ligand charge-transfer excited state and the reduced form of these compounds do not inject electrons into TiO2. Nanosecond transient absorption measurements demonstrate the formation of an extremely long-lived charge separated state based on equal concentrations of the reduced and oxidized compounds. The results are consistent with a mechanism of ultrafast excited-state injection into TiO2 followed by interfacial electron transfer to a ground-state compound. The quantum yield for this process was found to increase with excitation energy, a behavior attributed to stronger overlap between the excited sensitizer and the semiconductor acceptor states. For example, the quantum yields for [Os(bpy)2(dcbq)]/TiO2 were phi(417 nm) = 0.18 +/- 0.02, phi(532.5 nm) = 0.08 +/- 0.02, and phi(683 nm) = 0.05 +/- 0.01. Electron transfer to yield ground-state products occurs by lateral intermolecular charge transfer. The driving force for charge recombination was in excess of that stored in the photoluminescent excited state. Chronoabsorption measurements indicate that ligand-based intermolecular electron transfer was an order of magnitude faster than metal-centered intermolecular hole transfer. Charge recombination was quantified with the Kohlrausch-Williams-Watts model.