CO Shift Research Articles

Self-induced pressure shift and temperature dependence measurements of CO 2 at 2.05 μm with a tunable diode laser spectrometer

By using a high resolution tunable diode laser absorption spectrometer combined with a cryogenically cooled optical multi-pass cell, we have measured the self-induced pressure shift coefficients for 8 transitions in the R branch of the (20 01) III ← (00 00) I band of carbon dioxide around 2.05 μm. This spectral region is of particular interest for the monitoring of atmospheric CO 2 with Differential Absorption Lidars (DiAL). The measurement of these shift coefficients was realized at five different temperatures ranging from 218 to 292 K in order to determine their temperature dependence. The results are thoroughly compared to previous values reported in the literature for the (20 01) III ← (00 00) I band of CO 2. The temperature dependence of the self-induced pressure shifts are reported experimentally for the first time for this specific CO 2 band.

Resonance assignments and secondary structure of a phytocystatin from Ananas comosus

A cDNA encoding a cysteine protease inhibitor, cystatin was cloned from pineapple (Ananas comosus L.) stem. This clone was constructed into an expression vector and expressed in E. coli and purified to homogeneous. The recombinant pineapple cystatins (AcCYS) showed effectively inhibitory activity toward cysteine proteases including papain, bromelain, and cathepsin B. In order to unravel its inhibitory action from structural point of view, multidimensional heteronuclear NMR techniques were used to characterize the structure of AcCYS. The full (1)H, (15)N, and (13)C resonance assignments of AcCYS were determined. The secondary structure of AcCYS was identified by using the assigned chemical shift of (1)Hα, (13)Cα, (13)Cβ, and (13)CO through the consensus chemical shift index (CSI). The results of CSI analysis suggest 5 β-strands (residues 45-47, 84-91, 94-104, 106-117, and 123-130) and one α-helix (residues 55-73).

Role of metal components in Pd–Cu bimetallic catalysts supported on CeO2 for the oxygen-enhanced water gas shift

Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O2 is added to H2-rich reformate gas to enhance CO shift. Among CeO2-supported bimetallic catalysts, Pd–Cu and Pt–Cu combinations were found to show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H2 yield than WGS at low temperature around 250°C. Temperature programmed reduction (TPR) showed strong interaction between Pd and Cu in Pd–Cu/CeO2 by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO2. Extended X-ray absorption fine structure (EXAFS) analysis revealed that such bimetallic Pd–Cu and Pt–Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. Oxygen storage capacity (OSC) measurements point to higher resistance of Pd–Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd–Cu was found to promote CO shift, rather than CO oxidation by increasing the number of active sites and by suppressing H2 activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H2 and the loss of H2 by oxidation in OWGS. Transient response technique revealed that Cu in Pd–Cu enhances desorption of strongly chemisorbed CO2 on catalyst surface in contrast to very slow CO2 desorption from surface of monometallic Pd. Thus, the excellent OWGS activity of Pd–Cu catalyst has been attributed to the complementary roles of the two metals for enhancing CO shift, which is realized by its alloy structure and the accompanying strong interaction between metal components.

Direct wind measurements from November 2007 in Venus’ upper atmosphere using ground-based heterodyne spectroscopy of CO 2 at 10 μm wavelength

Between November 23 and 28, 2007, the Cologne Tuneable Heterodyne Infrared Spectrometer THIS was installed at the McMath-Pierce Solar Telescope (Kitt Peak, Arizona, USA) to determine zonal wind velocities and to estimate the subsolar-to-antisolar flow. We investigate dynamics in the upper atmosphere of Venus by measuring the Doppler shift of fully-resolved non-LTE CO 2 emission lines at 959.3917 cm −1 (10.423 μm), which probe a narrow altitude region in Venus’ atmosphere around 110 ± 10 km (∼1 μbar). The results show no significant zonal wind velocity at the equator. An increase with latitude up to 43 ± 13 m/s at a latitude of 33°N was observed. This confirms the deduction of a minor influence of Venus superrotation at an altitude of 110 km from previous measurements in May 2007 ( Sornig et al., 2008). The specific observing geometry enables estimating the maximum cross terminator velocity of the subsolar-to-antisolar flow at 72 ± 47 m/s.

Combined volumetric, infrared spectroscopic and theoretical investigation of CO 2 adsorption on Na-A zeolite

Adsorption isotherms of carbon dioxide on the Na-A zeolite were measured in the temperature range from 273 to 333 K. Henry’s constants and isosteric adsorption heats calculated from the temperature dependence of CO 2 isotherms were combined with results of the variable temperature IR spectroscopy to obtain a spectroscopic signature of adsorption complexes and corresponding thermodynamic characteristics. The adsorption of CO 2 in Na-A zeolite was also investigated computationally, using a periodic density functional model improved for the proper description of dispersion interactions. Based on a good agreement between experimental and calculated adsorption heats and shifts of asymmetric CO 2 stretching frequency due to adsorption the following model of CO 2/Na-A system is proposed: (i) CO 2 adsorption complexes formed at a low coverage involves interaction of CO 2 with three Na + cations in the LTA supercage; they are characterized by the IR band at 2349 cm −1. (ii) CO 2 adsorption complexes at higher coverages are formed between a pair of Na + cations; they are characterized by the IR band centered at 2360 cm −1. Almost half of the interaction energy between CO 2 and Na-A is due to the dispersion interaction.

A New Zealand record of sea level rise and environmental change during the Paleocene–Eocene Thermal Maximum

The global warming associated with the Paleocene–Eocene Thermal Maximum (PETM) ca. 55.5 Myr ago is the most dramatic identified short-term temperature increase of the Cenozoic. One direct consequence of a warming world is a rise in sea level, due primarily to the thermal expansion of water as oceans warmed. The Kumara-2 core, South Island, New Zealand, spans the Paleocene/Eocene transition and provides a rare southern hemisphere continental margin record of the PETM. Lithology, palynology and compound-specific stable isotope compositions of higher plant leaf wax n-alkanes reveal a 4.85 m PETM and a carbon isotope excursion (CIE) of ca. − 4.5‰, larger than the − 2.5 to − 3.5‰ CIEs generally recorded by deep sea foraminifera. There is a shift from a terrestrial to a marine, potentially anoxic, sedimentary depositional environment at the base of the PETM, interpreted as being the result of a local sea level rise. Coincident with the onset of the CIE is the appearance of pollen associated with thermophilic conditions and the development of Nypa mangrove swamps. Moreover, there is a reorganisation of the angiosperm pollen assemblage during the PETM, and an initial increase in fern spores and decrease in gymnosperms. Crucially, all of these changes occur below the horizon characterised by the most negative δ 13C values, suggesting that: 1) the recorded negative excursion of 4.5‰ may indeed reflect the shift in atmospheric CO 2 isotopic composition; and 2) that the large input of 13C-depleted carbon into the ocean–atmosphere system was not geologically instantaneous, with at least some of the added carbon lagging warming, sea level rise and vegetation change. Furthermore, compound-specific hydrogen isotope analyses show a large degree of variability both directly before and during the CIE, suggesting that the PETM in New Zealand was characterised by complex and transient changes in the hydrological regime, similar to those reported in North America, the Arctic and Eastern Africa. Thus, the new PETM record from Kumara-2 reveals local climatic and biotic responses, driven by a combination of global warming and the consequential change in local depositional environment induced by sea level rise.

Investigations on the behaviour of 2 kW natural gas fuel processor

In this paper, the first experimental investigations on a pre-commercial natural gas steam reformer have been presented. The fuel processor unit contains the elements as follows: desulfurizer, steam reformer reactor, CO shift converter, CO preferential oxidation (PROX) reactor, steam generator, burner and heat exchangers. The fuel processor produces 45 Nl/min of syngas in which the hydrogen concentration is about 75 vol.% and the other chemical species are nitrogen, carbon dioxide and methane. The CO concentration is below 1 ppmv, so that this reforming system is suitable for the integration with a PEM fuel cell stack. The experimental activity has been conducted in a test station, properly designed to measure the behaviour of the fuel processor. The laboratory test facility is equipped by a National Instruments Compact DAQ real-time data acquisition and control system running Labview™ software. Several measurement instruments and controlling devices have been installed. Furthermore, a gas chromatograph is used to measure the product gas composition during the tests. The aim of this work has been to analyze the behaviour of this pre-commercial steam reforming unit during its operation cycle in different operating conditions (full and partial loads) in order to study its integration with a PEM fuel cell for developing a high efficiency microcogeneration system for residential applications.

The Mn-doping effect on the charge ordering state of La 1/3Sr 2/3FeO 3

The longitudinal ultrasonic velocity ( V l ), as well as resistivity has been measured in single-phase polycrystalline La 1/3Sr 2/3Fe 1− x Mn x O 3 ( x = 0, 0.025, 0.05) at a frequency of 10 MHz, from 20 K to 300 K. It is found that with increasing Mn-doping level, the resistivity increases and the charge ordering transition temperature T CO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in V l above T CO and dramatic stiffening below T CO are observed. This abnormal elastic softening above T CO can be described well by the mean-field theory, which indicates that this feature is due to the electron–phonon coupling via the Jahn–Teller effect and this coupling is enhanced with the Mn doping. Below T CO, another softening in V l is observed for x = 0, and weakens with the increasing of Mn content. This character is attributed to the breathing-type distortion of Fe–O octahedron and suggests that the charge disproportionation (CD) transition is suppressed by the Mn substitution.

Labile soil carbon inputs mediate the soil microbial community composition and plant residue decomposition rates

Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities? In a 14 d laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g(-1) soil) to soils amended with and without (13) C-labeled plant residue. We measured CO(2) respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR). Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g(-1)) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g(-1)) had no impact on plant residue decomposition, while greater concentrations of C (>7.2 mg C g(-1)) reduced decomposition (-50%). Concurrently, high exudate concentrations (>3.6 mg C g(-1)) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (<3.6 mg C g(-1)) increased metabolic activity rather than gene copy numbers. These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.

Lorentz half-width, pressure-induced shift and speed-dependent coefficients in oxygen-broadened CO 2 bands at 6227 and 6348 cm −1 using a constrained multispectrum analysis

The McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak, Arizona, was used to record infrared high resolution absorption spectra of CO 2 spectra broadened by O 2. These spectra were analyzed to measure O 2-broadened half-width coefficients, O 2-induced pressure-shift coefficients and speed dependent parameters for transitions in the 30013←00001 and 30012←00001 bands of 16O 12C 16O located near 6227 and 6348 cm −1, respectively. All spectra were obtained at room temperature using the long path, 6 m base path White cell available at NSO. A multispectrum nonlinear least-squares fitting algorithm employing Voigt line shapes modified to include line mixing and speed dependence was used to fit simultaneously a total of 19 spectra in the 6120–6280 cm −1 (30013←00001) and 6280–6395 cm −1 (30012←00001) spectral regions. 16 of the 19 spectra analyzed in this work were self broadened and three spectra were lean mixtures of CO 2 in O 2. The volume mixing ratios of CO 2 in the three spectra varied between 0.06 and 0.1. Lorentz half-width and pressure-induced shift coefficients were measured for all transitions in the P(50)–R(50) range in both vibrational bands. The results obtained from present analysis have been compared with measurements available in the literature for self-, air-, oxygen- and argon-broadening. No significant differences were observed between the broadening and shift coefficients of the two bands. The N 2-broadened half-width and pressure-shift coefficients were computed from measured air- and O 2-broadened width and shift coefficients.

Interaction and Reaction of Coadsorbed NO and CO on a Rh(100) Single Crystal Surface

In order to assess the possibility to follow surface reactions in a quantitative way by vibrational spectroscopy, a combination of temperature programmed reaction spectroscopy (TPRS) and reflection absorption infrared spectroscopy (RAIRS) has been used to study the decomposition of NO and the reaction between NO and CO on Rh(100). NO adsorbs in two configurations: in an almost parallel position at coverages below 0.18 ML and, in addition, in an upright position, probably on a bridge site, at all coverages. Coadsorbing NO and CO has only a minor influence on NO binding, whereas CO shifts gradually from top toward the bridge site under the influence of NO. Combining TP-RAIRS with TPRS during the reaction between CO and NO enabled us to simultaneously study site occupation and obtain qualitative surface coverages and desorption rates. At low surface coverages, NO dissociation is observed at lower temperatures than CO(2) formation. Near saturation, NO dissociation becomes blocked and shifts up in temperature. NO dissociation occurs simultaneously with CO(2) formation. To decompose NO, free surface sites have to be generated through surface diffusion or desorption of some CO. During NO decomposition, the formed oxygen atoms react with CO to form CO(2), creating more empty sites. This may lead to an explosive surface reaction.

Constructability study on a German reference IGCC power plant with and without CO 2-capture for hard coal and lignite

This paper describes several cases of technical design, performance and an economic evaluation for IGCC-power plant concepts with and without CO 2 capture and storage (CCS) operated on world market hard coal and German lignite. Evaluations include IGCC concepts based on commercially available and competitive state-of-the-art technologies. In concept pre-assessment pressure concepts for heat recovery steam generation, configuration of air separation unit, gas conditioning alternatives and synthesis gas cooling in comparison to full water quench options for gas cooling were investigated. The economically most beneficial and efficient cases were evaluated identifying target values for carbon capture rate and plant efficiency. These requirements lead to the application of a HP/IP heat recovery system in gasification, a HP/IP/LP system in combined cycle, 70% air integration, sour CO shift conversion for hard coal and lignite cases with CCS and a full water quench in case for hard coal with CCS. The comparison between capture and non-capture cases shows a potential CO 2-avoidance of 89% in case of hard coal and 74% in case of lignite, respectively. The additional auxiliary consumption due to CCS leads to a decreasing net efficiencies based on LHV basis from 45.9% to 34.9% (hard coal) and from 51.5% to 41.3% (lignite). In case of hard coal the cost of electricity increases by 13.4% with the addition of carbon capture and in case of lignite by 11.8%, respectively. A sensitivity analysis for different factors affecting relative cost of electricity was carried out as well.

Microbial biomass, and dissolved organic carbon and nitrogen strongly affect soil respiration in different land uses: A case study at Three Gorges Reservoir Area, South China

In order to better understand the limiting factors and substrate affecting soil CO 2 flux, we measured total organic carbon (TOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) from seven sites of four land-use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest) of subtropical soils in Three Gorges Reservoir Area, China. Objectives were to (1) evaluate the separate and interactive relationship of TOC, MBC, MBN, DOC, and DON with soil CO 2 flux, in addition to the relationship obtained by environmental variables (soil temperature and moisture), and (2) investigate the seasonal and annual CO 2 fluxes from different land uses. Annual CO 2 fluxes ranged from 5.4 to 9.5 Mg CO 2 ha −1 year −1. Vegetable field had the highest CO 2 emission, while pine forest had significantly lower CO 2 emission than cultivated land uses. Different quantities of MBC and MBN significantly regulated the CO 2 emission among different land uses, relatively weakly correlated with DOC, while not being correlated with DON. However, temporal fluctuations of CO 2 flux were significantly regulated by MBC, MBN, DOC and DON, in one model of variation, in all land uses. But, when all the variables were included in the multiple stepwise regression analysis, different trend of dominancy was observed for soil temperature (two sites), MBC (one site), MBN (one site), DOC (two sites) and DON (one site). Our results indicate that (1) there can be a significant shift of microbial biomass with land-use change, which in turn, caused to shift in CO 2 flux, and (2) apart from the soil temperature, microbial biomass and dissolved organic substances must be considered in a warming future as these can explain a major part of temporal variation of soil CO 2 fluxes.

Pt,In and Pd,In catalysts for the hydrogenation of nitrates and nitrites in water. FTIR characterization and reaction studies

Pt,In and Pd,In catalysts supported on alumina or silica are active for the reduction of nitrate to N 2 in water, using H 2 as reducing agent. The characterization of the catalysts using FTIR of adsorbed CO shows the formation of both linear and bridged CO–Pd and CO–Pt bonds. Besides, carbonate species are formed due to the presence of OH groups provided by the support. The presence of In produces a shift in CO–Pd and CO–Pt bands, suggesting the formation of intermetallic particles. After use in reaction, the amount of CO–Pd and CO–Pt species strongly decreases, the main signals being those associated with carbonate groups. The proportion between bridged and linear species also changes after reaction. These results indicate the agglomeration of metallic particles during reaction, which is in agreement with TEM results. Increasing the In loading from 0.25 to 0.5 wt.% results in a moderate decrease in the nitrate conversion for all of the catalysts, which could be associated with a decrease of isolated Pd sites which are responsible for the dissociation of hydrogen. The experimental evidence for this point is the decrease of bridged CO adsorbed observed via FTIR for the samples with higher In loading and for all the catalysts. TPR experiments show low-temperature reduction peaks due to the presence of oxychloride and hydroxychloride particles in monometallic Pd and Pt catalysts. When In is present, the formation of Pd–In and Pt–In compounds provoke the shift of the reduction peaks and the appearance of new reduction signals.

Zwitterionic i-motif structures are preserved in DNA negatively charged ions produced by electrospray mass spectrometry

DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine) base pairs. Negatively charged ions of DNA i-motifs produced by electrospray mass spectrometry are therefore zwitterionic if the base pairing motif is preserved in the gas phase. Here we used IRMPD spectroscopy and ion mobility spectrometry to assess whether i-motif structures were preserved in the gas phase. We first investigated the IRMPD spectral signature of the tetramer [dC(6)](4), which can only be formed via C-H(+)-C base pairing, compared to the single strand dC(6). The IR signature of i-motif formation is an apparent broadening of the band at 1650 cm(-1). DFT calculations show this apparent broadening is actually due to blue-shifts of the NH(2) scissoring modes and red shifts of C[double bond, length as m-dash]O stretching modes. We then investigated the gas-phase conformations of the telomeric sequence d(CCCAAT)(3)CCC, that can form an intramolecular i-motif, by performing IRMPD spectroscopy and ion mobility spectrometry as a function of the charge state. We show that the negative ions of the lowest charge states correspond to a preserved i-motif structure. This is the first demonstration of the native extraction of solution-phase zwitterionic nucleic acids using negative electrospray ionization.

B107 DMEを利用した中低温廃熱の化学再生用触媒の実験的研究(OS3 省エネルギー・コジェネ技術),動力エネルギーシステム部門20周年,次の20年への新展開)

This work aims to realize combined heat and power (CHP) system enhanced by chemical recuperation of the unused waste heat at around 300 degree C that is commonly found in many industries. This system can "upgrade" the unused waste heat to electric energy by endothermic reaction of DME steam reforming and can save the fuel consumption and reduce CO_2 emission. We successfully prepared the catalyst customized to this purpose. DME steam reforming is the sequential reaction which consists of DME hydrolysis and methanol decomposition or steam reforming, and a few research reported that solid acid promotes the former reaction. We experimented with several combinations of zeolite and γ-alumina for solid acid and CoFe-spinel, CuMnCrK, CuMn-spinel and LaPd/CeO_2 for the latter reactions. The test results showed that zeolite had higher activity for DME hydrolysis and LaPd/CeO_2 selectively produced CO by suppressing CO shift reaction at 300 degree C. The LHV of reformed gas increased by 8.7% compared to that of DME fuel.

Interactive effects of iron, irradiance and CO 2 on Ross Sea phytoplankton

We conducted a factorial shipboard continuous culture experiment to examine the interactive effects of altered iron, irradiance and CO 2 on the summer phytoplankton community of the Ross Sea, Antarctica. After 18 days of continuous incubation, iron enrichment increased phytoplankton biomass, nutrient drawdown, diatom and Phaeocystis abundance, and some photosynthetic parameters. High irradiance significantly increased the number of Phaeocystis antarctica colonies, as well as P. antarctica abundance relative to diatoms. Iron and light had significant interactive effects on diatom and P. antarctica pigment concentrations, P. antarctica colony abundance, and Si:N, Si:C, and N:P ratios. The major influence of high CO 2 was on diatom community structure, by favoring the large centric diatom Chaetoceros lineola over the small pennate species Cylindrotheca closterium. The ratio of centric to pennate diatoms was significantly responsive to changes in all three variables individually, and to all of their possible two- and three-way combinations. These results suggest that shifts in light, iron, and CO 2 and their mutual interactions all play a role in controlling present day Ross Sea plankton community structure, and need to be considered when predicting the possible future responses of biology and biogeochemistry in this region.

Partial oxidation of methanol over copper catalysts supported on rice husk ash

Abstract Copper catalysts supported on rice husk ash (Cu/RHA) were tested for partial oxidation of methanol (POM) to produce H 2 . The catalysts were prepared by deposition–precipitation and characterized by ICP-AES, TGA, XRD, TPR, XPS and N 2 O titration techniques. The Cu/RHA catalyst with 10.2 wt.% Cu loading and under 673 K calcination has higher copper dispersion and smaller Cu particle size. This catalyst exhibits higher activity and selectivity for POM to produce H 2 . The partial pressure of O 2 plays an important role to determine the product distribution. Catalytic activity of the catalyst at different reaction temperatures shows that CH 3 OH conversion, H 2 selectivity and CO selectivity increase with rise in temperature. At different temperatures along with POM, several reactions such as methanol combustion, steam reforming of methanol, methanol decomposition, water gas shift and oxidation of CO and H 2 might be involved. Comparison of catalytic activity of Cu/RHA and Cu/SiO 2 catalysts demonstrates that Cu/SiO 2 catalysts deactivate with time with faster rate and have higher CO selectivity. This proves that Cu/RHA catalysts have good thermal stability and selectivity for POM to produce H 2 .

Solvation Structures of cis- and trans-1,2-Dichloroethylene in Supercritical CO2 Investigated by Raman Spectroscopy and Attractive Energy Calculations

Vibrational Raman spectra of the C horizontal lineC stretching modes of cis- and trans-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical carbon dioxide (CO(2)). The spectra were collected at a fixed solute mole fraction by varying the fluid density by a factor of 20. As the density increased, the peak frequencies of the C horizontal lineC stretching modes shifted toward the low-energy side at isotherms of reduced temperature, T(r) = T/T(c) = 1.02, 1.06, and 1.20. By analyzing these density dependences using the perturbed hard-sphere theory, we decomposed the shifts into attractive and repulsive components. The repulsive shifts of cis-C(2)H(2)Cl(2) were almost equivalent to those of trans-C(2)H(2)Cl(2). However, the attractive shifts of nonpolar trans-C(2)H(2)Cl(2) were significantly greater than those of polar cis-C(2)H(2)Cl(2) at all densities and temperatures. To evaluate the difference in the isomers, we calculated the attractive shifts of the C horizontal lineC stretching modes of each isomer, composing of dispersion, dipole-induced-dipole, and dipole-quadrupole interactions between solute C(2)H(2)Cl(2) and solvent CO(2) molecules. These three interactions were quantified by considering molecular configurations and orientations, and solvation structures around the isomers were elucidated by 3D schematic diagrams. As a result, it was shown that the anisotropic solvation structure around trans-C(2)H(2)Cl(2) was responsible for the larger attractive shifts in the supercritical CO(2). The difference of solvation structures between the isomers was significant at T(r) = 1.02 but became minor as the temperature increased to T(r) = 1.20.

Ligand Reactivity in Diarylamido/Bis(Phosphine) PNP Complexes of Mn(CO)3and Re(CO)3

The syntheses of meridionally ligated tricarbonyl complexes (PNP)Mn(CO)(3) and (PNP)Re(CO)(3) are described (PNP = [2-P(CHMe(2))(2)-4-MeC(6)H(3)](2)N(-)). Cyclic voltammograms show reversible one-electron redox couples for both parent compounds (-0.34 V vs Cp(2)Fe(0/+) for (PNP)Mn(CO)(3), -0.25 V vs Cp(2)Fe(0/+) for (PNP)Re(CO)(3)), and chemical oxidation with AgOTf results in formation of the corresponding paramagnetic triflate salts [(PNP)Mn(CO)(3)]OTf and [(PNP)Re(CO)(3)]OTf. Electron paramagnetic resonance spectra and computational results indicate that this event is primarily ligand centered; allylation of the organic ligand moiety of [(PNP)Mn(CO)(3)]OTf with allyltributylstannane is consistent with this assignment. The oxidation (PNP)Mn(CO)(3) to [(PNP)Mn(CO)(3)]OTf results in a shift in average CO stretching frequency of 30 cm(-1); protonation of (PNP)Mn(CO)(3) with TfOH to form [(PNHP)Mn(CO)(3)]OTf results in a similar magnitude shift.