Spectroscopy, thermal desorption, double

The apparatuses used for the studies of both ammonia synthesis emd hydrodesulfurization were almost identical, consisting of a UHV chamber pumped by both ion and oil diffusion pumps to base pressures of 1 x10 " Torr. Each chamber was equipped with Low Energy Electron Diffraction optics used to determine the orientation of the surfaces and to ascertain that the surfaces were indeed well-ordered. The LEED optics doubled as retarding field analyzers used for Auger Electron Spectroscopy. In addition, each chamber was equipped with a UTI 100C quadrupole mass spectrometer used for analysis of background gases and for Thermal Desorption Spectroscopy studies. 

Figure 1. Thermal desorption temperature Td as a function of the Pauling electronegativity [20]. Closed and open circles indicate the series of single-cation borohydrides M(BH4) (M = Li, Na, Mg, Zn, Sc, and Zr n = 1-4) and double-cation ones ZrLi .4(BH4) (n = 4 (Zr(BH4)4), 5 and 6), examined by gas chromatography (GC) and quadrupole mass spectroscopy (QMS), respectively. There is a difference between Td of LiBH4/ZrBH4 determined using GC (approximately 800 K) and that determined using QMS (approximately 740 K), owing to a longer distance between the detector and sample, and also to a lower gas flow rate, in GC.

Thermal electrocyclizations of perhalogenated 1,3-butadienes yield perhalogenated cyclobutenes which can be solvolysed to 3,4-dihydroxy-3-cydobutene-l,2-dione ( squaric acid") and its derivatives (G. Maahs, 1966 H. Knorr, 1978 A.H. Schmidt, 1978). Double CO extrusion from fused cyclobutenediones has been used to produce cycloalkynes, e.g., benzyne from benzocyclobutenedione by irradiation in an argon matrix (O.L. Chapman, 1973) and cyc/o-Ci8, cyclo-Cn, etc. by laser desorption mass spectroscopy of appropriate precursors (see section 4.9.8). 

As virtually all biological molecules possess low vapour pressures gas-phase molecular spectroscopy methods to investigate isolated neutral biomolecules require volatilization methods other than thermal evaporation. The combination of laser desorption with a supersonic molecular beam expansion together with the selectivity of IR and UV double resonance methods opened up the possibility of characterizing isolated, neutral biomolecules and their clusters with the biological environment. 

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