Home-made thermal desorption unit as an aid in gas chromatographic/mass spectormetric identification of environmental pollutants

The design, assembly and operation of a home-made thermal desorption unit is described. A special effort was made to obtain a system which does not require a substantial modification of the standard split/splitless inlet port of the gas chromatograph. As a consequence, a change-over to the split/splitless analysis of liquid samples can be done quickly and easily, thereby improving the cost-effectiveness of analysis by gas chromatography/mass spectrometry. Its analytical performance is shown to be adequate for both identification and determination of trace components.     

Determination of stoichiometry of vanadium oxides by 14-MeV neutron activation

A method was developed for the determination of oxygen/vanadium ratios in vanadium oxides by 14-MeV neutron activation analysis by means of the reactions ⁵¹V(n, p)⁵¹Ti and ¹⁶O(n, p)¹⁶N. A linear relationship between activity ratios and weight ratios of six mixtures composed of vanadium carbide and oxalic acid was obtained with a precision of 0.18% after suitable corrections for /gg- and β-ray absorption. Four commercial vanadium oxides and three specially prepared vanadium oxides were analyzed. The V/O ratio varied between 1.980 and 3.015. The percent standard deviation on these values was between 0.53% and 1.09%.     

Nuclear ground state spins of short-lived strontium isotopes

Nuclear ground state spins of the odd-mass strontium isotopes between A=79 and 97 were determined by measurements of the hyperfine structure in the ionic transition 5s²S_1/2?5p²P_3/2. The spins of⁹³Sr and⁹⁷Sr are revised to I=5/2 and I=1/2, respectively, while assignments for the remaining isotopes are confirmed.     

β-NMR in II–VI semiconductors

β-active probe nuclei are implanted in nominally undoped ZnSe crystals. β-radiation detected nuclear magnetic resonance (β-NMR) studies are described for two different probe nuclei, ⁸Li and ¹²B. This way, the implantation behavior of two “opposite”dopants, one acceptor (Li) and one donor (B) can be characterized by the same microscopic technique. Such characterizations are attempted in terms of the structure of intermediate or final lattice sites, defect charge states, or the kinetics of defect reactions and site changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

The quadrupole moment of the neutron-halo nucleus11Li

The quadrupole moment ratio of⁹Li and¹¹Li was measured by a combination of in-beam laser induced nuclear polarization and Β-NMR in LiNbO₃. The result ¦Q(¹¹Li)/Q(⁹Li)¦=1.14(16) is consistent with cluster models describing¹¹Li as composed of a⁹Li core and a far extended halo of two loosely bound neutrons.     

Sensitive laserspectroscopy on ions with hyperfine split transitions

Collinear laser—fast alkaline-earth ion beam interaction can be monitored sensitively by a detection sequence consisting of optical pumping to a metastable state, state-dependent neutralization, and separate counting of ions and atoms. Deceleration of the ions prior to neutralization strongly increases the sensitivity of the method. For ions with hyperfine split transitions the sensitivity can be considerably improved by a two-step optical pumping sequence. In this contribution, the results of rate equation calculations are compared to experimental results for Ba-and Sr-beams, including a shortlived⁹⁹Sr beam of very low intensity.     

Adsorption of Propene on Neutral Gold Clusters in the Gas Phase

The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Au_n?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Au_n–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C₃H₆ on Au_n is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed.