Abstract. We report the first results of the unbiased spectral high resolution survey obtained towards Sgr B2 with the Long Wavelength Spectrometer on board ISO. The survey detected more than one hundreds lines from several molecules. Ammonia is the molecule with the largest number (21) of detected lines in the survey. We detected NH3 transitions from levels with energies from 45 to 500 cm −1 . The detected transitions are from both para and ortho ammonia and metastable and non-metastable levels. All the ammonia lines are in absortion against the FIR continuum of Sgr B2. With such a large number of detected lines in such a large range of energy levels, we could very efficiently constrain the main parameters of the absorbing gas layer. The gas is at (700 ± 100) K and has a density lower than 10 4 cm −3 . The total NH3 column density in the layer is (3 ± 1) × 10 16 cm −2 , equally shared between ortho and para ammonia. Given the derived relatively high gas temperature and ammonia column density, our observations support the hypothesis previously proposed of a layer of shocked gas between us and Sgr B2. We also discuss previous observations of far infrared line absorption from other molecules, like H2O and HF, in the light of this hot absorbing layer. If the absorption is done by the hot absorbing layer rather than by the warm envelope surrounding Sgr B2, as was previously supposed in order to interpret the mentioned observations, the derived H2O and HF abundances are one order of magitude larger than previously estimated. Yet, the present H2O and HF observations do not allow one to disentangle the absorption from the hot layer against the warm envelope. Our conclusions are hence that care should be applied when interpreting the absorption observations in Sgr B2, as the hot layer clearly seen in the ammonia transitions may substantially contribute to the absorption.

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A Laser Ion Mobility Spectrometer has been set up and trace detection experiments have been performed. We find that laser ionization almost selectively ionizes aromatic hydrocarbons. Aliphatic hydrocarbons are only laser-ionized in case these contain conjugated double bonds. As, in contrast to radioactive ion mobility spectrometry, background air constituents and air contaminants cannot be ionized, drift spectra are inherently simple and easily interpretable. We show that a laser ion mobility spectrometer can be operated in two basically different modes, either using tunable or fixedfrequency laser sources. In the tunable laser mode, aromatic hydrocarbons can be detected in the positive mode and distinguished from each other on account of their different excitation wavelengths and ion drift times. In the fixedfrequency mode, specially chosen and intentionally admitted aromatic hydrocarbons are laser ionized and the primary ionization is transferred to non-aromatic species by means of atmospheric pressure chemical ionization. In this latter mode of operation nitroglycerin and triacetone triperoxide, two nonaromatic high explosives, could be detected.

Basic aspects of fast atom bombardment mass spectrometry such as matrix effects, discriminatory effects between positive and negative ion formation, sensitivity, and isotope dilution have been investigated using oligopeptides and amino acid derivatives as model compounds. The matrix selected was found to have a decisive influence on the sensitivity of fast atom bombardment. Acidic and basic properties of the samples could be correlated with different ionization efficiencies in positive or negative ion formation. With respect to sensitivity, a roughly linear relation between signal intensity and sample amount was observed in the range of lng to 10 pg of sample. Nanogram amounts of samples could be detected by fast atom bombardment mass spectrometry. Finally, the suitability of fast atom bombardment for quantitative investigations is proven by the investigation of isotopically labelled mixtures.

Deep dry etch processes for GaAs and GaSb are investigated. Reactive ion etching in Cl2/Ar plasma discharges is used to pattern GaAs and GaSb with a single-layer soft mask resist. Soft masks have many advantages over (metal) hard masks such as easy and inexpensive processing, low pinhole density, and high etching reproducibility. Using TI35ES, an image reversal resist developed by MicroChemicals, GaAs etch profiles of up to 25 μm depth and GaSb structures of more that 50 μm depth are obtained revealing considerable dimensional stability. Even for etch durations of more than 50 min the resist can be easily removed from the sample surface after the etch process. Roughnesses of etched surfaces of less than 1 nm (rms, measured by atomic force microscopy) are obtained after reactive ion etching for both materials. Photoluminescence measurements reveal that the surface stoichiometry is conserved during the etching step. Deep dry etching of GaAs and GaSb can be exploited for example to fabricate fiber or capillary connections to and between optoelectronic devices or to create substrate windows for backside-illuminated photodetectors in the infrared wavelength range.