Preparation of SnS2/MoS2with p-n heterojunction for NO2sensing.

Conventional metal sulfide (SnS2) gas-sensitive sensing materials still have insufficient surface area and slow response/recovery times. To increase its gas-sensing performance, MoS2nanoflower was produced hydrothermally and mechanically combined with SnS2nanoplate. Extensive characterization results show that MoS2was effectively integrated into SnS2. Four different concentrations of SnS2-MoS2composites were evaluated for their NO2gas sensitization capabilities. Among them, SnS2-15% MoS2at 170 °C demonstrated the greatest response values to NO2, 7.3 for 1 ppm NO2, which is about three times greater than the SnS2sensor at 170 °C (2.58). The creation of pn junctions following compositing with SnS2was determined to be the primary reason for the composite's faster recovery time, while the heterojunction allowed for the rapid separation of hole-electron pairs. Because the MoS2surface has multiple vacancy defects, the adsorption energy of these vacancies is significantly higher than that of other places, resulting in increased NO2adsorption. Furthermore, MoS2can serve as active adsorption sites for SnS2micrometer sheets during gas sensing. This study may help to build new NO2gas sensors.

Effect of fluorine doping on the NO2-sensing properties of MoS2nanoflowers.

The somewhat slow recovery kinetics of NO2sensing at low temperatures are still challenging to overcome. To enhance the gas sensing property, fluorine is doped to MoS2nanoflowers by facile hydrothermal method. Extensive characterization data demonstrate that F was effectively incorporated into the MoS2nanoflowers, and that the microstructure of the MoS2nanoflowers did not change upon F doping. The two MoS2doped with varying concentrations of fluorine were tested for their sensing property to NO2gas. Both of them show good repeatability and stability. A smaller recovery time was seen in the F-MoS2-1 sample with a little amount of F loading, which was three times quicker than that of pure MoS2. The key reason for the quicker recovery time of this material was found to be the fluorine ions that had been adsorbed on the surface of F-MoS2-1 would take up some of the NO2adsorption site. Additionally, the sample F-MoS2-2 with a higher F doping level demonstrated increased sensitivity. The F-MoS2-2 sensor's high sensitivity was mostly due to the lattice fluorine filled to the sulfur vacancy, which generated impurity levels and reduced the energy required for its electronic transition. This study might contribute to the development of new molybdenum sulfide based gas sensor.

Au- or Ag-Decorated ZnO-Rod/rGO Nanocomposite with Enhanced Room-Temperature NO2-Sensing Performance.

To improve the gas sensitivity of reduced oxide graphene (rGO)-based NO2 room-temperature sensors, different contents (0-3 wt%) of rGO, ZnO rods, and noble metal nanoparticles (Au or Ag NPs) were synthesized to construct ternary hybrids that combine the advantages of each component. The prepared ZnO rods had a diameter of around 200 nm and a length of about 2 µm. Au or Ag NPs with diameters of 20-30 nm were loaded on the ZnO-rod/rGO hybrid. It was found that rGO simply connects the monodispersed ZnO rods and does not change the morphology of ZnO rods. In addition, the rod-like ZnO prevents rGO stacking and makes nanocomposite-based ZnO/rGO achieve a porous structure, which facilitates the diffusion of gas molecules. The sensors' gas-sensing properties for NO2 were evaluated. The results reveal that Ag@ZnO rods-2% rGO and Au@ZnO rods-2% rGO perform better in low concentrations of NO2 gas, with greater response and shorter recovery time at the ambient temperature. The response and recovery times with 15 ppm NO2 were 132 s, 139 s and 108 s, 120 s, and the sensitivity values were 2.26 and 2.87, respectively. The synergistic impact of ZnO and Au (Ag) doping was proposed to explain the improved gas sensing. The p-n junction formed on the ZnO and rGO interface and the catalytic effects of Au (Ag) NPs are the main reasons for the enhanced sensitivity of Au (Ag)@ZnO rods-2% rGO.

Convergence and divergence emerging in climatic controls of polynomial trends for northern ecosystem productivity over 2000-2018.

Recent rapid warming has caused uneven impacts on the composition, structure, and functioning of northern ecosystems. It remains unknown how climatic drivers control linear and non-linear trends in ecosystem productivity. Based on a plant phenology index (PPI) product at a spatial resolution of 0.05° over 2000-2018, we used an automated polynomial fitting scheme to detect and characterize trend types (i.e., polynomial trends and no-trends) in the yearly-integrated PPI (PPIINT) for northern (> 30°N) ecosystems and their dependence on climatic drivers and ecosystem types. The averaged slope for the linear trends (p < 0.05) of PPIINT was positive across all the ecosystems, among which deciduous broadleaved forests and evergreen needle-leaved forests (ENF) showed the highest and lowest mean slopes, respectively. More than 50% of the pixels in ENF, arctic and boreal shrublands, and permanent wetlands (PW) had linear trends. A large fraction of PW also showed quadratic and cubic trends. These trend patterns agreed well with estimates of global vegetation productivity based on solar-induced chlorophyll fluorescence. Across all the biomes, PPIINT in pixels with linear trends showed lower mean values and higher partial correlation coefficients with temperature or precipitation than in pixels without linear trends. Overall, our study revealed the emergence of latitudinal convergence and divergence in climatic controls on the linear and non-linear trends of PPIINT, implying that northern shifts of vegetation and climate change may potentially increase the non-linear nature of climatic controls on ecosystem productivity. These results can improve our understanding and prediction of climate-induced changes in plant phenology and productivity and facilitate sustainable management of ecosystems by accounting for their resilience and vulnerability to future climate change.

Engineering of ZnO/rGO towards NO2 Gas Detection: Ratio Modulated Sensing Type and Heterojunction Determined Response.

Nanoscale heterostructured zinc oxide/reduced graphene oxide (ZnO/rGO) materials with p-n heterojunctions exhibit excellent low temperature NO2 gas sensing performance, but their doping ratio modulated sensing properties remain poorly understood. Herein, ZnO nanoparticles were loaded with 0.1~4% rGO by a facile hydrothermal method and evaluated as NO2 gas chemiresistor. We have the following key findings. First, ZnO/rGO manifests doping ratio-dependent sensing type switching. Increasing the rGO concentration changes the type of ZnO/rGO conductivity from n-type (<0.6% rGO) to mixed n/p -type (0.6~1.4% rGO) and finally to p-type (>1.4% rGO). Second, interestingly, different sensing regions exhibit different sensing characteristics. In the n-type NO2 gas sensing region, all the sensors exhibit the maximum gas response at the optimum working temperature. Among them, the sensor that shows the maximum gas response exhibits a minimum optimum working temperature. In the mixed n/p-type region, the material displays abnormal reversal from n- to p-type sensing transitions as a function of the doping ratio, NO2 concentration and working temperature. In the p-type gas sensing region, the response decreases with increasing rGO ratio and working temperature. Third, we derive a conduction path model that shows how the sensing type switches in ZnO/rGO. We also find that p-n heterojunction ratio (np-n/nrGO) plays a key role in the optimal response condition. The model is supported by UV-vis experimental data. The approach presented in this work can be extended to other p-n heterostructures and the insights will benefit the design of more efficient chemiresistive gas sensors.

Cross-sectoral impacts of the 2018-2019 Central European drought and climate resilience in the German part of the Elbe River basin.

The 2018-2019 Central European drought was probably the most extreme in Germany since the early sixteenth century. We assess the multiple consequences of the drought for natural systems, the economy and human health in the German part of the Elbe River basin, an area of 97,175 km2 including the cities of Berlin and Hamburg and contributing about 18% to the German GDP. We employ meteorological, hydrological and socio-economic data to build a comprehensive picture of the drought severity, its multiple effects and cross-sectoral consequences in the basin. Time series of different drought indices illustrate the severity of the 2018-2019 drought and how it progressed from meteorological water deficits via soil water depletion towards low groundwater levels and river runoff, and losses in vegetation productivity. The event resulted in severe production losses in agriculture (minus 20-40% for staple crops) and forestry (especially through forced logging of damaged wood: 25.1 million tons in 2018-2020 compared to only 3.4 million tons in 2015-2017), while other economic sectors remained largely unaffected. However, there is no guarantee that this socio-economic stability will be sustained in future drought events; this is discussed in the light of 2022, another dry year holding the potential for a compound crisis. Given the increased probability for more intense and long-lasting droughts in most parts of Europe, this example of actual cross-sectoral drought impacts will be relevant for drought awareness and preparation planning in other regions. Supplementary Information: The online version contains supplementary material available at 10.1007/s10113-023-02032-3.

The confounding effect of snow cover on assessing spring phenology from space: A new look at trends on the Tibetan Plateau.

The Tibetan Plateau is the highest and largest plateau in the world, hosting unique alpine grassland and having a much higher snow cover than any other region at the same latitude, thus representing a "climate change hot-spot". Land surface phenology characterizes the timing of vegetation seasonality at the per-pixel level using remote sensing systems. The impact of seasonal snow cover variations on land surface phenology has drawn much attention; however, there is still no consensus on how the remote sensing estimated start of season (SOS) is biased by the presence of preseason snow cover. Here, we analyzed SOS assessments from time series of satellite derived vegetation indices and solar-induced chlorophyll fluorescence (SIF) during 2003-2016 for the Tibetan Plateau. We evaluated satellite-based SOS with field observations and gross primary production (GPP) from eddy covariance for both snow-free and snow covered sites. SOS derived from SIF was highly correlated with field data (R2 = 0.83) and also the normalized difference phenology index (NDPI) performed well for both snow free (R2 = 0.77) and snow covered sites (R2 = 0.73). On the contrary, normalized difference vegetation index (NDVI) correlates only weakly with field data (R2 = 0.35 for snow free and R2 = 0.15 for snow covered sites). We further found that an earlier end of the snow season caused an earlier estimate of SOS for the Tibetan Plateau from NDVI as compared to NDPI. Our research therefore adds new evidence to the ongoing debate supporting the view that the claimed advance in land surface SOS over the Tibetan Plateau is an artifact from snow cover changes. These findings improve our understanding of the impact of snow on land surface phenology in alpine ecosystems, which can further improve remote sensing based land surface phenology assessments in snow-influenced ecosystems.

The missing pieces for better future predictions in subarctic ecosystems: A Torneträsk case study.

Arctic and subarctic ecosystems are experiencing substantial changes in hydrology, vegetation, permafrost conditions, and carbon cycling, in response to climatic change and other anthropogenic drivers, and these changes are likely to continue over this century. The total magnitude of these changes results from multiple interactions among these drivers. Field measurements can address the overall responses to different changing drivers, but are less capable of quantifying the interactions among them. Currently, a comprehensive assessment of the drivers of ecosystem changes, and the magnitude of their direct and indirect impacts on subarctic ecosystems, is missing. The Torneträsk area, in the Swedish subarctic, has an unrivalled history of environmental observation over 100 years, and is one of the most studied sites in the Arctic. In this study, we summarize and rank the drivers of ecosystem change in the Torneträsk area, and propose research priorities identified, by expert assessment, to improve predictions of ecosystem changes. The research priorities identified include understanding impacts on ecosystems brought on by altered frequency and intensity of winter warming events, evapotranspiration rates, rainfall, duration of snow cover and lake-ice, changed soil moisture, and droughts. This case study can help us understand the ongoing ecosystem changes occurring in the Torneträsk area, and contribute to improve predictions of future ecosystem changes at a larger scale. This understanding will provide the basis for the future mitigation and adaptation plans needed in a changing climate.

New satellite-based estimates show significant trends in spring phenology and complex sensitivities to temperature and precipitation at northern European latitudes.

Recent climate warming has altered plant phenology at northern European latitudes, but conclusions regarding the spatial patterns of phenological change and relationships with climate are still challenging as quantitative estimates are strongly diverging. To generate consistent estimates of broad-scale spatially continuous spring plant phenology at northern European latitudes (> 50° N) from 2000 to 2016, we used a novel vegetation index, the plant phenology index (PPI), derived from MODerate-resolution Imaging Spectroradiometer (MODIS) data. To obtain realistic and strong estimates, the phenology trends and their relationships with temperature and precipitation over the past 17 years were analyzed using a panel data method. We found that in the studied region the start of the growing season (SOS) has on average advanced by 0.30 day year-1. The SOS showed an overall advancement rate of 2.47 day °C-1 to spring warming, and 0.18 day cm-1 to decreasing precipitation in spring. The previous winter and summer temperature had important effects on the SOS but were spatially heterogeneous. Overall, the onset of SOS was delayed 0.66 day °C-1 by winter warming and 0.56 day °C-1 by preceding summer warming. The precipitation in winter and summer influenced the SOS in a relatively weak and complex manner. The findings indicate rapid recent phenological changes driven by combined seasonal climates in northern Europe. Previously unknown spatial patterns of phenological change and relationships with climate drivers are presented that improve our capacity to understand and foresee future climate effects on vegetation.

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping.

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni0.962Sn0.038O1.038, and then decreased to 12.24 for Ni0.946Sn0.054O1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

Wide bandgap mesoporous hematite nanowire bundles as a sensitive and rapid response ethanol sensor.

In this study, α-Fe2O3 nanowires were synthesized using mesoporous SBA-15 silica as the hard templates with the nanocasting method, and then mesoporous α-Fe2O3 nanowire bundles (NWBs) were separated from the well-dispersed α-Fe2O3 nanowires (NWs) by the centrifugation technique. Both samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm and UV-vis spectra. All results indicated that the α-Fe2O3 NWBs with mesoporous structure presented a higher BET surface area (95 m(2) g(-1)) and wider bandgap (2.08 eV) than those of α-Fe2O3 NWs (32 m(2) g(-1) and 1.91 eV). The bandgap of α-Fe2O3 NWBs was in accordance with the bulk α-Fe2O3, while the BET surface area was much higher. The results from the gas-sensing measurement revealed that the α-Fe2O3 NWBs based gas sensor exhibited a high sensitivity of 21.7, fast response-recovery of 7.5 s and 1 s, and good selectivity to ethanol at 340 °C. The sensitivity (21.7) for ethanol of α-Fe2O3 NWBs was much better than that of the α-Fe2O3 NWs (12.2), which should be attributed to the higher BET surface area and wider bandgap of α-Fe2O3 NWBs.

Preparation and Characterization of Graphene/Fe3O4 Composites by Solvothermal Method.

In the present study, graphene/Fe3O4 nanocomposites were prepared by solvothermal method using graphite oxide (GO) and FeCl3 x 6H2O as starting materials and the products were characterized by X-ray Diffraction (XRD), Scanning Electronic Microscope (SEM) and Vibrating Sample Magnetometer (VSM). Effects of Fe ion concentration, temperature and time of solvothermal reaction on the magnetic properties, microstructures and morphologies of graphene/Fe3O4 nanocomposites were investigated. The results showed that with the raising of Fe ion, particle size of the products became bigger, and saturation magnetization of the products got higher. The saturation magnetization and particle size of the products can be enhanced by increasing the reaction time and temperature, but the change of saturation magnetization and particle size were not obvious after the time got 8 h and temperature was at 200 degrees C, which demonstrated that the products became stable under this condition. The morphologies, microstructures and properties of products can be controlled by adjusting synthesis conditions.

Isolation and crystallographic characterization of Sm@C2v(3)-C80 through cocrystal formation with Ni(II)(octaethylporphyrin) or bis(ethylenedithio)tetrathiafulvalene.

Sm@C(2v)(3)-C(80) has been separated from the carbon soot produced by electrical arc vaporization of graphite rods doped with Sm(2)O(3) and purified. Its structure has been determined by single crystal X-ray diffraction using cocrystals obtained from either Ni(II)(octaethylporphyrin) (Ni(II)(OEP)) to form Sm@C(2v)(3)-C(80)·Ni(II)(OEP)·1.68(toluene)·0.32(benzene) or bis(ethylenedithio)-tetrathiafulvalene (ET) to produce Sm@C(2v)(3)-C(80)·ET·0.5(toluene). Thus, this study offers the first opportunity to compare a common endohedral fullerene in two different cocrystals. Both cocrystals provide consistent information on the basic structure of Sm@C(2v)(3)-C(80) but show that the distribution of samarium ion sites inside the carbon cage depends upon whether Ni(II)(OEP) or ET is present. The samarium ion is disordered in both structures, but the prominent sites lie slightly off the 2-fold symmetry axis of the cage. Computational studies at the B3LYP level indicate that Sm@C(2v)(3)-C(80) is more stable than any of the other six isomers of Sm@C(80) that obey the isolated pentagon rule (IPR). The surface electrostatic potential of the interacting components in the cocrystals has been examined to identify factors responsible for the ordering of the fullerene cages. The regions of the Ni(II)(OEP) or ET molecules that are closest to the fullerene display negative potential, while the corresponding regions of the endohedral fullerene show positive potential in a consistent fashion in both cocrystals.

X-ray crystallographic characterization of new soluble endohedral fullerenes utilizing the popular C82 bucky cage. Isolation and structural characterization of Sm@C3v(7)-C82, Sm@C(s)(6)-C82, and Sm@C2(5)-C82.

Three isomers of Sm@C(82) that are soluble in organic solvents were obtained from the carbon soot produced by vaporization of hollow carbon rods doped with Sm(2)O(3)/graphite powder in an electric arc. These isomers were numbered as Sm@C(82)(I), Sm@C(82)(II), and Sm@C(82)(III) in order of their elution times from HPLC chromatography on a Buckyprep column with toluene as the eluent. The identities of isomers, Sm@C(82)(I) as Sm@C(s)(6)-C(82), Sm@C(82)(II) as Sm@C(3v)(7)-C(82), and Sm@C(82)(III) as Sm@C(2)(5)-C(82), were determined by single-crystal X-ray diffraction on cocrystals formed with Ni(octaethylporphyrin). For endohedral fullerenes like La@C(82), which have three electrons transferred to the cage to produce the M(3+)@(C(82))(3-) electronic distribution, generally only two soluble isomers (e.g., La@C(2v)(9)-C(82) (major) and La@C(s)(6)-C(82) (minor)) are observed. In contrast, with samarium, which generates the M(2+)@(C(82))(2-) electronic distribution, five soluble isomers of Sm@C(82) have been detected, three in this study, the other two in two related prior studies. The structures of the four Sm@C(82) isomers that are currently established are Sm@C(2)(5)-C(82), Sm@C(s)(6)-C(82), Sm@C(3v)(7)-C(82), and Sm@C(2v)(9)-C(82). All of these isomers obey the isolated pentagon rule (IPR) and are sequentially interconvertable through Stone-Wales transformations.

Aqua-(2,6-dihy-droxy-benzoato-κO(1))bis-(1,10-phenanthroline-κ(2)N,N')manganese(II) 2,6-dihy-droxy-benzoate hemihydrate.

In the complex cation of the title compound, [Mn(C(7)H(5)O(4))(C(12)H(8)N(2))(2)(H(2)O)](C(7)H(5)O(4))·0.5H(2)O, the Mn(II) atom has a six-coordinate octa-hedral environment defined by one carboxyl-ate O atom belonging to a 2,6-dihy-droxy-benzoate (DHB) ligand, four N atoms from two chelating 1,10-phenanthroline mol-ecules and one water mol-ecule. The lattice water mol-ecule lies on a twofold rotation axis. Intra-molecular O-H⋯O hydrogen bonds are present in the DHB anions and complex cations. Inter-molecular O-H⋯O hydrogen bonds link two cations, two anions and one water mol-ecule into a dimer. π-π inter-actions between the pyridine and benzene rings and between the benzene rings are also observed [centroid-centroid distances = 3.7774 (16), 3.7912 (16) and 3.7310 (17) Å].

Single samarium atoms in large fullerene cages. Characterization of two isomers of Sm@C92 and four isomers of Sm@C94 with the X-ray crystallographic identification of Sm@C1(42)-C92, Sm@C(s)(24)-C92, and Sm@C3v(134)-C94.

Two isomers of Sm@C(92) and four isomers of Sm@C(94) were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3). Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni(II)(octaethylporphyrin) reveals the identities of two of the Sm@C(92) isomers: Sm@C(92)(I), which is the more abundant isomer, is Sm@C(1)(42)-C(92), and Sm@C(92)(II) is Sm@C(s)(24)-C(92). The structure of the most abundant form of the four isomers of Sm@C(94), Sm@C(94)(I), is Sm@C(3v)(134)-C(94), which utilizes the same cage isomer as the previously known Ca@C(3v)(134)-C(94) and Tm@C(3v)(134)-C(94). All of the structurally characterized isomers obey the isolated pentagon rule. While the four Sm@C(90) and five isomers of Sm@C(84) belong to common isomerization maps that allow these isomers to be interconverted through Stone-Wales transformations, Sm@C(1)(42)-C(92) and Sm@C(s)(24)-C(92) are not related to each other by any set of Stone-Wales transformations. UV-vis-NIR spectroscopy and computational studies indicate that Sm@C(1)(42)-C(92) is more stable than Sm@C(s)(24)-C(92) but possesses a smaller HOMO-LUMO gap. While the electronic structures of these endohedrals can be formally described as Sm(2+)@C(2n)(2-), the net charge transferred to the cage is less than two due to some back-donation of electrons from π orbitals of the cage to the metal ion.

Isolation of three isomers of Sm@C84 and X-ray crystallographic characterization of Sm@D(3d)(19)-C84 and Sm@C2(13)-C84.

Three isomers with the composition Sm@C(84) were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3). These isomers were labeled Sm@C(84)(I), Sm@C(84)(II), and Sm@C(84)(III) in order of their elution times during chromatography on a Buckyprep column with toluene as the eluent. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni(II)(octaethylporphyrin) reveals the identities of two of the isomers: Sm@C(84)(I) is Sm@C(2)(13)-C(84), and Sm@C(84)(III) is Sm@ D(3d)(19)-C(84). Sm@C(84)(II) can be identified as Sm@C(2)(11)-C(84) on the basis of the similarity of its UV/vis/NIR spectrum with that of Yb@C(2)(11)-C(84), whose carbon cage has been characterized by (13)C NMR spectroscopy. Comparison of the three Sm@C(84) isomers identified in this project with two prior reports of the preparation and isolation of isomers of Sm@C(84) indicate that five different Sm@C(84) isomers have been found and that the source of samarium used for the generation of fullerene soot is important in determining which of these isomers form.

An optical sensor network for vegetation phenology monitoring and satellite data calibration.

We present a network of sites across Fennoscandia for optical sampling of vegetation properties relevant for phenology monitoring and satellite data calibration. The network currently consists of five sites, distributed along an N-S gradient through Sweden and Finland. Two sites are located in coniferous forests, one in a deciduous forest, and two on peatland. The instrumentation consists of dual-beam sensors measuring incoming and reflected red, green, NIR, and PAR fluxes at 10-min intervals, year-round. The sensors are mounted on separate masts or in flux towers in order to capture radiation reflected from within the flux footprint of current eddy covariance measurements. Our computations and model simulations demonstrate the validity of using off-nadir sampling, and we show the results from the first year of measurement. NDVI is computed and compared to that of the MODIS instrument on-board Aqua and Terra satellite platforms. PAR fluxes are partitioned into reflected and absorbed components for the ground and canopy. The measurements demonstrate that the instrumentation provides detailed information about the vegetation phenology and variations in reflectance due to snow cover variations and vegetation development. Valuable information about PAR absorption of ground and canopy is obtained that may be linked to vegetation productivity.

Large endohedral fullerenes containing two metal ions, Sm2@D2(35)-C88, Sm2@C1(21)-C90, and Sm2@D3(85)-C92, and their relationship to endohedral fullerenes containing two gadolinium ions.

The carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3) contains a series of monometallic endohedral fullerenes, Sm@C(2n), along with smaller quantities of the dimetallic endohedrals Sm(2)@C(2n) with n = 44, 45, 46, and the previously described Sm(2)@D(3d)(822)-C(104). The compounds Sm(2)@C(2n) with n = 44, 45, 46 were purified by high pressure liquid chromatography on several different columns. For endohedral fullerenes that contain two metal atoms, there are two structural possibilities: a normal dimetallofullerene, M(2)@C(2n), or a metal carbide, M(2)(µ-C(2))@C(2n-2). For structural analysis, the individual Sm(2)@C(2n) endohedral fullerenes were cocrystallized with Ni(octaethylporphyrin), and the products were examined by single-crystal X-ray diffraction. These data identified the three new endohedrals as normal dimetallofullerenes and not as carbides: Sm(2)@D(2)(35)-C(88), Sm(2)@C(1)(21)-C(90), and Sm(2)@D(3)(85)-C(92). All four of the known Sm(2)@C(2n) endohedral fullerenes have cages that obey the isolated pentagon rule (IPR). As the cage size expands in this series, so do the distances between the variously disordered samarium atoms. Since the UV/vis/NIR spectra of Sm(2)@D(2)(35)-C(88) and Sm(2)@C(1)(21)-C(90) are very similar to those of Gd(2)C(90) and Gd(2)C(92), we conclude that Gd(2)C(90) and Gd(2)C(92) are the carbides Gd(2)(µ-C(2))@D(2)(35)-C(88) and Gd(2)(µ-C(2))@C(1)(21)-C(90), respectively.