Stanislaw Halas

Work functions of elements expressed in terms of the Fermi energy and the density of free electrons

On the basis of Brodies definition of the work function and the length of spontaneous polarization of plasma, the following new formula for calculation of the work functions of elements has been derived: , where is the electron density parameter expressed in units of the Bohr radius, is the Fermi energy and is an empirical constant ( for the alkali metals, Ca, Sr, Ba, Ra and Tl, whereas for the remaining elements). The density parameter was calculated from the atomic mass, the bulk density of the element and the assessed number of free electrons per atom which is equal to the nominal valence of the element or, in the case of transition metals, close to this number (within ). The values obtained by using the above formula are in excellent agreement with experimental data for pure-metal polycrystalline surfaces, within 5% in most cases. A table with the work functions and with complete input data for most of the elements is presented.

Oceanic stable isotope composition and a scenario for the Permo‐Triassic crisis

Stable carbon isotope data from brachiopod shells from the Upper Permian Kapp Starostin Formation (West Spitsbergen) indicate that the oceanic carbon isotopic ratio, which had already been very high in the late Permian, rapidly increased by almost 4 per mil and then dramatically declined by more than 10 per mil in the very latest Permian. This pattern is essentially repeated by the oxygen isotope curve. These data show that a geologically rapid switch between two fundamentally different states of the Earths exosystem occurred near the Permo‐Triassic transition. The late Permian state of the global system was profoundly different from the modern one in that vast amounts of organic carbon were stored, presumably in the form of easy‐to‐mobilize sapropel‐like deposits, below the oceanic redoxcline. Under such conditions—which we propose to call overfed ocean—nutrients were intensely recycled to seawater, thus allowing the ocean to sustain a huge standing crop of the biosphere. Deposition of large amounts of ...

Inter-laboratory calibration of new silver orthophosphate comparison materials for the stable oxygen isotope analysis of phosphates

Stable oxygen isotope compositions (δ(18)O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off-line oxygen extraction in the form of CO(2) which was analyzed on a dual inlet and triple collector isotope ratio mass spectrometer, while labs (2) and (3) employed an isotope ratio mass spectrometer coupled to a high-temperature conversion/elemental analyzer (TC/EA) where Ag(3)PO(4) samples were analyzed as CO in continuous flow mode. The δ(18)O values for the proposed new comparison materials were linked to the generally accepted δ(18)O values for Vennemanns TU-1 and TU-2 standards as well as for Ag(3)PO(4) extracted from NBS120c. The weighted average δ(18)O(VSMOW) values for the new comparison materials UMCS-1, UMCS-2 and AGPO-SCRI were determined to be + 32.60 (± 0.12), + 19.40 (± 0.12) and + 14.58 (± 0.13)‰, respectively.

Experimental determination of carbon isotope equilibrium fractionation between dissolved carbonate and carbon dioxide

By mixing aliquots of pure Na2CO3 and CO2, solutions with precisely known molal fractions of CO3=, HCO3−, and dissolved CO2 were prepared. The apparent fractionation factor between gaseous CO2 and total carbon in the solution was determined mass spectrometrically from which the CO3= − CO2 fractionation factor was calculated taking into account the known fraction of HCO3− and respective isotope fractionation. Although the measurements have been made for a rather narrow temperature range, from 4 to 80°C, a theoretical curve was fitted through the experimental points, and thereby, tge isotopic partition function ratio of 13CO3= and 12CO3= molecules has been obtained for an extended temperature range. The results obtained for CO3=−CO2 isotope fractionation are significantly lower than those for HCO3−−CO2 exchange (with 103(α − 1) = 5.0 ± 0.2 at 25°C and cross-over point at about 63°C).

An automatic inlet system with pneumatic changeover valves for isotope ratio mass spectrometer

The system described incorporates two pneumatically operated changeover valves, of a new design, with electrically heated capillaries in the dual-inlet system, which reduce the instrumental effects of this system to a negligible level. The changeover valves show many advantages such as high accuracy of closure, fast establishment of steady conditions after switching, simple construction and automatic control. Information on installation of stainless steel capillaries is also included.

Stable carbon and oxygen isotope record in the Paleogene La Meseta Formation, Seymour Island, Antarctica

Stable carbon and oxygen isotopic relations have been analysed in brachiopod, gastropod, and bivalve fossils from the La Meseta Formation (Eocene-?early Oligocene), Seymour (Marambio) Island, West Antarctica. The results indicate a shift in δ 13 C by 6 permil beginning in the middle part of the Unit II of the formation. This shift may imply a change from a largely stratified to a vigorously mixed ocean. Such an interpretation is corroborated by changes in the elemental proportions in the shell material. Alternatively, the carbon isotopic shift may be regarded as reflecting a change in the local depositional enviornment. Such an interpretation agrees with isotopic data from the Weddell Sea, which do not confirm the pattern observed in the La Meseta Formation. In any event, the oxygen isotopic curve does not decline parallel to the carbon curve and may thus imply a considerable climatic cooling event. This effect is so profound that it might be interpreted as evidence for glaciation, especially when taking into account the fact that this phenomenon coincides with the well-known cooling trend throughout the Eocene. If this interpretation is correct, the hypothesized Glaciation may possibly be correlated with the Polonez Glaciation, the largest Cenozoic glaciation known in the Antarctic Peninsula sector. Alternatively, it may be regarded as a local phenomenon, predating development of the icesheet.

Thermal work function shifts for polycrystalline metal surfaces

Abstract A new approach is presented for the calculation of the thermal shifts of the work functions of polycrystalline metal surfaces by including the thermal expansion of the metal into the electron density parameter as well as Fermi energy. Calculations of d ϕ /d T as a function of temperature are performed for 74 elements, encompassing a total of 103 cases of various temperature ranges, phases and (in a few cases) orientations. It is shown that for a majority of metals d ϕ /d T is not a constant over a broad temperature range. Comparison of theoretical and experimental values indicates that the thermal lattice vibrations do not influence d ϕ /d T significantly. Our results would suggest that the use of a Kelvin probe to measure the thermal variation of ϕ may be problematic.

Diurnal cycle of carbon isotope ratio in soil CO2 in various ecosystems

Our investigations of diurnal variations of the 13C/12C ratio and CO2 content in soil air were carried out in three environments during periods of high biosphere activity. It has been observed that diurnal variation of CO2 concentration is negatively correlated δ13. Particularly great variations occurred at shallow soil depths (10–30 cm) when the plant cover activity was high while the soil temperature was rather low. Under such conditions the δ13 variations had the magnitude of 4‰, while the CO2 concentration varied more than doubly. The maximum of the 13C/12C ratlo and the minimum of the CO2 concentration in a cultivated field with winter wheat took place in the afternoon, whereas in deciduous forest similar patterns were observed at dawn. In these cases soil temperatures at 10 cm depths varied less than 2°C. Hence, under wheat the variation in root respiration rate seem to be the main reason of the recorded varations. In an uncultivated grass-field during the hottest period in summer we did not measure any distinct variations of CO2 properties in spite of the fact that soil temperature varied up to 5°C. This might be due to dominant microbial respiration at the high soil temperature, which exceeded 20°C.

INFLUENCE OF FREEZING AND THAWING ON THE CARBON ISOTOPE COMPOSITION IN SOIL CO2

The carbon isotopic composition of soil CO2 was measured during the winter of 1990/91 at two sites in the Lublin Upland (Poland). In that season a period with very low air temperature occurred, during which snow covered soils were frozen. We observed variations of δ13C up to 3 permil. During freezing periods the variations depended on soil physical properties. In sandy soil the 13C12C ratio during freezing periods increased, while in loess soil it decreased. This appears to be connected with the granulometrical composition of the soil and the size of the pores, which influence the rate of CO2 diffusion into the atmosphere. During thawing periods, when the snow was melting, the CO2 concentration increased and the 13C12C ratios decreased in both types of the soil under investigation due to worse contact of soil horizons with the atmosphere. The major winter variations in δ13CO2 of soil may be useful natural markers of infiltrating waters.

An inexpensive device for digital measurements of isotopic ratios

A typical double collecting mass spectrometer was greatly improved by the use of a device which enables automatic measurements of isotopic ratios in digital form to be carried out. The system consists of two electrometers with high value resistors being automatically replaced by capacitors for the ratio measurements. Thus noise produced by the resistors is eliminated. The electrometer output signals are digitised by a digital voltmeter, and the digits plus some additional information are transferred to a calculator printing the signals and their ratio.