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We present a review of our recent measurements of total cross sections (Q
T's) for the scattering of positrons by Na, K, and Rb, and positronium-formation cross sections (Q
Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For ourQ
Ps measurements, our approach involves setting upper and lower limits onQ
Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the scattering cell. Comparison with theoretical calculations shows that our measuredQ
T's andQ
Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in then=1 andn=2 states. In the 3–10 eV energy range, this calculation predicts a peak in theQ
T's andQ
Ps's for K which also appears in our measurements. The absence of such a peak in our measuredQ
T's andQ
Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations ofQ
T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and RbQ
T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb. 相似文献
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Mary E. R. McHale Ann-Sofi M. Kauppila Joyce R. Powell Pablo Otero Jr. Melani Jayasekera William E. Acree Jr. 《Journal of solution chemistry》1996,25(3):295-302
Experimental solubilities are reported for benzil dissolved in six binary mixtures containing dibutyl ether with hexane, heptane, octane, cyclohexane, methylcyclohexane, and 2,2,4-trimethylpentane at 25°C. Results of these measurements are compared to the predictions of equations developed previously for solubility in systems of nonspecific interactions. The most successful equation in terms of goodness of fit involved a volume fraction average of the excess Gibbs energies relative to the Flory-Huggins model, and predicted the experimental solubilities in the six systems studied to within an overall average absolute deviation of 3.4% and with a maximum deviation of 6.0%. 相似文献
4.
We have recently measured total cross sections for 5 to 302 eV positrons scattered by atomic hydrogen using a beam transmission technique. A check for consistency is made between these measurements and prior measurements of positronium formation and ionization cross sections by making use of available theoretical calculations of elastic and excitation cross sections for positron-atomic hydrogen scattering. 相似文献
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Mary E. R. McHale Joyce R. Powell Ann-Sofi M. Kauppila William E. Acree Jr. Pierre L. Huyskens 《Journal of solution chemistry》1996,25(11):1089-1104
Experimental solubilities are reported for anthracene dissolved in eight binary mixtures containing 2-ethoxyethanol with 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 1-pentanol, 3-methyl-1-butanol and 1-octanol, and also in binary 1-pentanol+2-methoxyethanol and 2-methyl-1-propanol+2-propoxyethanol solvent systems at 25°C. Results of these measurements, combined with previously reported anthracene solubility data in 22 different alcohol +2-alkoxyethanol (2-methoxyethanol, 2-propoxyethanol and 2-butoxyethanol) solvent mixtures, are used to test the limitations and applications of expressions derived from Mobile Order theory. The first predictive expression assumes only formation of homogeneous self-associated hydrogen-bonded species, whereas the second equation includes additional terms to account for heterogeneous complex formation between the dissolved alcohol and 2-alkoxyethanol solvent molecules. Both equations predict the observed anthracene solubilities to within an average absolute deviation of about 3%. 相似文献
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Joyce R. Powell Mary E. R. McHale Ann-Sofi M. Kauppila William E. Acree Jr. Scott W. Campbell 《Journal of solution chemistry》1996,25(10):1001-1017
A relatively simple expression is developed for predicting the solubility of an inert crystalline solute in binary alcohol + alcohol solvent mixtures based upon the Kretschmer-Wiebe association model. The predictive accuracy of the newlyderived expression is compared to equation(s) derived previously from Mobile Order theory using experimental anthracene solubilities in seven binary alcohol + 1-pentanol solvent mixtures at 25°C, which were measured as part of the present investigation. Computations show that both models accurately describe the solubility behavior of anthracene in the binary solvent systems studied. Average absolute deviations between observed and predicted values were 0.9% and 1.4% for the Kretschmer-Wiebe and Mobile Order predictive equations, respectively. 相似文献
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Tiina?J.?Kauppila Andries?P.?BruinsEmail author Risto?Kostiainen 《Journal of the American Society for Mass Spectrometry》2005,16(8):1399-1407
In the novel atmospheric pressure photoionization-mass spectrometry the ionization efficiency has been observed to decrease
when the solvent flow rate is increased. The effect of the flow rate on the ionization efficiency was studied by comparing
the behavior of two analytes, one of which is ionized through charge exchange, the other through proton transfer. Additional
information about the ion loss mechanisms was obtained by comparing results obtained with two different APPI ion sources:
a Sciex prototype and the Agilent/Syagen APPI source. In addition to the measurements done by using the mass analyzer, the
total ion current in the ion source was obtained by measuring the currents of the ions arriving at curtain/end plate and orifice/capillary
of the two mass spectrometers. The total ion current measurements showed a significant decrease at high solvent flow rates.
Loss of dopant radical cations was thought to be the reason for the signal decrease of the analytes formed through charge
exchange. Analytes formed through proton transfer were not as seriously ected by the high solvent flow rates, but some saturation
of their signal was nevertheless observed. Loss of photons through absorption by solvent vapor is another mechanism that can
be held responsible for a reduction of the total number of ions produced by the APPI source. 相似文献