We report the investigation of the 3s ← 2p transition in the BAr 2 cluster. In a supersonic expansion of B atoms entrained in Ar, at high beam source backing pressures we observe several features in the fluorescence excitation spectrum which cannot be assigned to the BAr diatom. Using BAr(X, B) potential energy curves which reproduce our experimental observations on this molecule and an Ar-Ar interaction potential, we employ a pairwise additive model, along with variational and diffusion Monte-Carlo treatments of the nuclear motion, to determine the lowest vibrational state of the BAr 2 cluster. A subsequent simulation of the fluorescence excitation spectrum reproduces nearly quantitatively the strongest feature in our experimental spectrum not assignable to BAr.Because of the barrier in the BAr(B 2 Σ + ) potential energy curve, the 3s ← 2p transition in the BAr 2 is predicted to have an asymmetric profile, as is found experimentally.

Several methods for the quantitative determination of different forms of arsenic (Asl", As", monomethyl and dimethyl) in a variety of samples are described and compared. In each instance separation is achieved by chromatographic means, using either gas (GC) or high-performance liquid chromatography (HPLC), with detection by atomic spectrometry, namely flame atomic absorption spectrometry (FAAS), flame atomic fluorescence spectrometry (FAFS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). For the GC separation it is necessary to derivatise the As compounds either as the hydrides or as the methylthioglycolates. As the arsenic hydrides can be pre-concentrated using cryogenic trapping, this yields the lowest detection limits. The As species studied can be separated without derivatisation by HPLC but after HPLC separation hydride generation can be used to increase the sensitivity for FAAS, FAFS and ICP-AES.While each technique is best suited to certain applications, the hydride generation -cryogenic trapping -GC -FAAS system is capable of detection at the sub-p.p.b. level (0.22-0.55 ng absolute for different species) and is preferred for low-level As samples. When levels permit, HPLChydride generation -FAAS is probably the simplest routine method and HPLChydride generation -ICP-AES will probably be preferred for multielement analysis.

The coupling of a high-performance liquid chromatograph with a sensitive and selective laser-excited atomic fluorescence spectrometry (LEAFS) detector is described. In connection with this, a study of the signal and noise characteristics of instrumentation for dispersive, nondispersive, and front surface LEAFS is reported together with a comparison of the sensitivity and selectivity achieved with high-performance liquid chromatography (HPLC)-flame LEAFS, HPLC-ultraviolet (UV), and HPLC-continuum source excited flame atomic fluorescence spectrometry (AFC) instrumentation. The HPLC-flame LEAFS instrumentation was applied to an investigation of the Mn species responsible for (methylcyclopentadienyl)manganese tricarbonyl (MMT) toxicity in rats. The detection limits for various organomanganese species by HPLC-flame LEAFS ranged from 8 to 22 pg of manganese. Recovery of these compounds from rat urine varied between 80% and 100%, with a reproducibility of between 4% and 8% relative standard deviation. Preliminary data for the HPLC-flame LEAFS determination of toxic alkyltin compounds are reported.

Pump laser .I. Pump laser repetition rate Dye lasers Dye laser cell design

Tetramethyllead (TML) has been produced from inorganic lead salts using biologically active sediments and waters from the Tamar Estuary, S.W. England. The TML production was a twostage process involving an initial lag phase of about 100 hours followed by the exponential appearance of TML, which amounted to about 0.03% of total added lead. The methylation process is discussed in the context of lead transport in estuaries