We investigated the role of K+channels and intracellular Ca2+stores in the relaxations induced by the NO donor 3-morpholinosydnonimine (SIN-1) and 8-bromo-cGMP (8-BrcGMP), 8-(4-chlorophenylthio)-cGMP (pCPT-cGMP), and α,β-methylene-ATP in isolated segments of rat ileum. The inhibitory responses to SIN-1 and the cGMP analogs were not influenced by the K+blockers apamin, charybdotoxin, iberiotoxin, or glibenclamide, whereas relaxations induced by α,β-methylene-ATP were abolished by apamin and tetraethylammonium. The NO-donor SIN-1 and the cGMP analogs were able to inhibit contractions induced by activation of L-type Ca2+channels (BAY-K-8644), by carbachol (CCh), and by cyclopiazonic acid (CPA), a blocker of sarcoplasmic Ca2+-ATPase. However, the inhibition of the combined CPA and CCh response was reduced and the dose-response curve of SIN-1 shifted to the right. Intracellular Ca2+stores were emptied by incubation in Ca2+-free buffer and repetitive stimulation with CCh or BAY-K-8644. After restoration of extracellular Ca2+, the inhibitory effect of SIN-1 and pCPT-cGMP was only attenuated, whereas in the additional presence of CPA, the inhibitory effect of SIN-1 was blocked and the effect of 8-BrcGMP reduced. Thus depleting intracellular Ca2+stores attenuated the effect of SIN-1 and 8-BrcGMP, suggesting an involvement of functional Ca2+stores.

The motor activity of gastrointestinal smooth muscle is closely related to the membrane potential. Controlling the membrane potential via modulation of K+ channels is essential for the action of neurotransmitters on smooth muscle. In the present study the effect of the K+ channel activator, lemakalim, on longitudinal smooth muscle of the rat ileum was investigated. Segments of rat ileum were stimulated by the muscarinic receptor agonist, carbachol (10(-6) M). Lemakalim (10(-10) to 3 x 10(-5) M) induced a dose-dependent inhibition of the carbachol-induced contraction. This inhibitory effect of lemakalim was not modified by neural blockade with tetrodotoxin (10(-6) M, n = 9). Glibenclamide (10(-7) to 10(-5) M), a specific blocker of ATP-dependent K+ channels antagonized dose dependently the relaxant effect of lemakalim (IC50: 3.4 x 10(-6) M, n = 11, P < 0.001). In contrast, apamin (10(-7) M, n = 9, n.s.) and charybdotoxin (10(-7) M, n = 9, n.s.), specific blockers of Ca2+-dependent K+ channels and the non-specific K+ channel blocker, tetraethylammonium (10(-4) to 10(-1) M), had no influence on the inhibitory effect of lemakalim. Contractions induced by the Ca2+ channel activator, Bay-K-8644, were completely inhibited by lemakalim (10(-5) M, n = 12). This inhibitory effect was also selectively antagonized by glibenclamide (10(-5) M). Potential non-adrenergic non-cholinergic (NANC) inhibitory mediators like ATP, nitric oxide (NO) or neurotensin showed no sensitivity to glibenclamide. These functional data indicate that the relaxant effect of lemakalim is due to a specific activation of glibenclamide-sensitive K+ channels, which in turn can modulate the activity of dihydropyridine-sensitive (voltage-dependent) Ca2+ channels. A physiological or pathophysiological role of the glibenclamide-sensitive K+ channels in intestinal smooth muscle is discussed; however, they seem not to be involved in the effect of the NANC inhibitory mediators tested.

The x-ray-absorption near-edge structure (XANES) of sulfur hexafluoride, SF6, in the gas phase has been measured with high energy resolution at the sulfur L2,3 and fluorine K ionization thresholds using synchrotron radiation from the SX700/II monochromator at BESSY. Besides dominant transitions to core-excited inner-well states, several series of Rydberg states with vibrational fine structure were resolved below the sulfur L 2,3 thresholds. Using the Rydberg formula, quantum defects of delta(s) = 1.80 and delta(d) = -0.03 were obtained for the s and d Rydberg orbitals of the central sulfur atom. A Franck-Condon analysis was used to determine the vibrational spacing and the S-F bond length of the (S 2p3/2)(-1)4s1 core-excited state. The presence of vibronically coupled transitions below the sulfur L2,3 edges was confirmed. The derived natural linewidths of the (S 2P1/2,3/2)-1 Rydberg states were found to be strikingly narrower than those of the (S 2p1/2,3/2)-1 inner-well resonances. Line-shape analysis also revealed significant inhomogeneous broadening of the (S 2p1/2,3/2)-1a1g1 states, which is attributed to unresolved vibrational structure. Large Lorentzian contributions to the line shapes of the (S 2P1/2,3/2)-1t2g1, resonances suggest that vibrational effects are relatively small for those states.

For the open-shell molecule NO, high-resolution photoionization studies of N 1s and O 1s core excitations to antibonding π* and nonbonding Rydberg orbitals were performed. In each case three vibrationally split 1 s2π*→1s(π*)2 transitions were observed, caused by the interactions of the π* electrons, as well as two Rydberg series with 3Π and 1Π character. An unambiguous assignment of all observed resonances is given. A Franck—Condon analysis of some of the observed spectral profiles yields vibrational frequencies and equilibrium internuclear distances of the various core-excited states of NO.

Inner-shell soft-x-ray absorption of formaldehyde, H2CO, in the region of the C K and O K absorption thresholds was studied with high energy resolution using synchrotron radiation from the SX700/II monochromator at BESSY. The absorption spectra were recorded via the total photocurrent yield. The C 1s-excitation spectrum is characterized by a dominant C 1s-1 pi* resonance and weaker transitions into Rydberg states, each exhibiting vibrational fine structure that is quantitatively analyzed in terms of the normal vibrational modes of H2CO. Isotopic effects on the vibrational modes were studied by taking analogous spectra of D2CO. A Franck-Condon analysis of the vibrationally split spectra yields equilibrium distances, molecular bond angles, and vibrational frequencies of C 1s-1-excited formaldehyde, which show strong isotopic effects. In addition, the ground vibrational level of the lowest Rydberg state (C 1s(-1)3s-a1) exhibits a pronounced shift to higher excitation energies upon replacement of H by D. This shift, as well as a considerable isotope-dependent line broadening, are presumably caused by perturbations of this state by valence orbitals. Analogous isotopic effects were observed for the O 1s(-1)3s-a1 Rydberg state.

This article reports on the high-resolution performance of the grazing-incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universität Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5-μm exit slit. We report on high-resolution gas-phase studies in the double-excitation region of He, as well as at core-excitation thresholds of Ne, Ar, Kr, and Xe in the photon-energy range from ≂45 eV to ≂900 eV. In addition, high-resolution core-excitation spectra at the K thresholds of C, N, and O are presented for gas-phase CO, N2, and O2. In all cases, high-n Rydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further improvements in resolution with this monochromator.

High-resolution photoionization studies of He have revealed more than 50 states below the N = 2-7 thresholds of He+, including sixteen (sp,2n+) and five (sp,2n-) states in the N = 2 series. With a resolving power of E/DELTA-E congruent-to 10 000, states as narrow as 0.1 meV could be observed and linewidths were determined with an accuracy up to +/- 0.5 meV. Interchannel interferences, evident through effects on positions, shapes, and intensities of Rydberg lines, were interpreted within the framework of the multichannel quantum-defect theory.

The results of a comparative study of the unoccupied density of states of CsI by analysis of the inelastic part of the photoelectron spectra, as well as the x-ray-absorption near-edge structure and inverse-photoemission spectra, are presented. It is found that valuable information on unoccupied electronic states in semiconductors or insulators may be obtained from an analysis of the spectral features in the low-kinetic-energy region of photoemission spectra caused by multiply-phonon-scattered electrons.

The results of a high-resolution photoabsorption study at the K thresholds of C and O are reported for CO/Al(111). Polarization effects on the C1s−1π∗ resonance show that the CO molecules are oriented parallel to the surface only in a relatively narrow range of submonolayer coverages around a dosage of ~ 0.6 L. At higher coverages, a second species of CO molecules is suggested oriented straight-up or tilted. The vibrationally-resolved spectra of the C1s−1π∗ resonance reveal a weakening of the intra-molecular bonding in the core-excited state for this second species relative to gas-phase CO.

Extended x-ray-absorption fine-structure measurements, low-energy electron diffraction, and Auger-electron spectroscopy have been applied to study preparation-dependent room-temperature Co/Si(100) interface formation. Evaporation of Co onto chemically etched and annealed Si(100) (2 X 1) leads up to about 0.5 monolayer coverage for adsorption of Co in the fourfold-hollow sites of the locally unreconstructed Si(100) surface. At higher coverages Co atoms occupy interstitial (adamanthane) and substitutional sites of the Si lattice. Annealing at T = 550-650-degrees-C for 5 min induces the diffusion of Co into the Si lattice, where Co atoms reside in adamanthane sites only. After evaporation of Co onto sputter-annealed Si(100) (2 X 1), only the formation of a locally ordered CoSi2-like phase could be observed in the measured coverage regime between 0.8 and 14 monolayers.

The local structure of thin technologically relevant co-sputtered amorphous Mo-Si films of near disilicide stoichiometry was determined by extended x-ray-absorption fine-structure measurements. The films are composed of small clusters characterized by a disilicide-like short-range order. In addition, we have investigated the Mo/Si(100) interface formation. The Mo/Si(100) interface is weakly reactive. Auger-electron-spectroscopy data indicate a rapid evolution of a Mo-metal layer above the substrate. The local atomic structure around the Mo atoms was found to depend on the surface-preparation method. In contrast to sputter-annealed Si(100) surfaces, where only the formation of a disilicide-like structure could be observed after evaporation of 3 monolayers of Mo, chemical wafer cleaning leads at the same coverage to the formation of a locally ordered Mo-metal structure above a thin reacted silicide layer.

Using synchrotron radiation, Auger electron, and H+/D+-ion yields have been studied at and above the O 1s excitation energies for condensed H2O/D2O layers of varying thickness, and for two reproducible adsorbate layers (so-called bilayers and monolayers) on Ru(001). Decay electron spectra as well as polarization dependences, angular distributions, and energy distributions of desorbing ions have been investigated. For polarizations with sufficient E component perpendicular to the surface, a sharp peak in the H+ NEXAFS spectrum is seen for all layers which has no direct counterpart in the Auger NEXAFS spectra, and whose intensity maximizes for E oriented in the detection direction. This observation is interpreted as due to the 1a1→4a1 core-to-bound transition of the surface molecules whose final state decays electronically and dissociates on comparable time scales. This appears to have the consequence that the symmetry of the coupled excitation is different from that expected for the primary photoabsorption process. There appears also to be an influence of hydrogen bonding on these effects. Similarities and differences between the various layers investigated are also analyzed.

The fine structure of C2H4 molecules in the (1s-1, π*) state is resolved using a plane grating ellipsoidal mirror grazing incidence monochromator at the storage ring BESSY. Two vibrational series can be identified, assigned to C-C and C-H vibrations. The natural line width of the (1s-1, π*) state was found to be 160 meV for condensed C2H4 multilayers. For submonolayers of C2H4 molecules on Ag(100) and Cu(100) this value was found to increase to 280 and 700 meV respectively. A shift to lower energies of the ground state transition is observed for the adsorbed molecules with respect to the multilayer case.

(1990). Spectral resolution in the soft‐X‐ray region up to 11,000. Synchrotron Radiation News: Vol. 3, No. 5, pp. 21-22.

High-resolution, high-intensity photoionization studies were performed near the carbon and oxygen K-edges of gas-phase CO. At least 37 absorption lines were resolved at the carbon K-edge, and new information was obtained about the π*, Rydberg, and double-excitation resonances, including Rydberg states up to n=7 and vibrational transitions up to v′ = 3. Vibrational structure in oxygen is 1s−1π* and Rydberg states was resolved for the first time. The derived molecular structure parameters are consistent with the Z+1 approximation. High-resolution, high-intensity core-level photoabsorption promises new opportunities in vibrational state-to-state chemistry and surface science.

Using plane grating, ellipsoidal mirror, grazing incidence monochromators at the storage ring BESSY, a resolution of ≦ 150meV was achieved for a photon energy of 285 eV. This high energy resolution considerably extends the range of possible studies using core level Spectroscopy. Some of the new opportunities are illustrated at the CK edge by resolving the vibrational fine structure of condensed C2H4 multilayers in the (1s−1, π*) state by means of photoabsorption spectroscopy. For the sake of comparison with other high resolution instruments, the vibrational fine structure of condensed N2 multilayers at the NK edge (∼ 400eV) was also measured, yielding a resolving power of 3000.

EXAFS measurements on the O 1 s edge of different silicon oxides show for the first time, that the SiO4 tetrahedra of native oxides are elongated along the surface normal and compressed in the plane. To follow the oxidation of silicon NEXAFS has been proven to be a useful tool.

MoSi2 is one of the main silicides used in semiconductor technology. In the present synchrotron study the local environment around the Mo atom in various Mo-Si systems was investigated by analyzing the EXAFS above the Mo LII edge. Because of the interference of the LII EXAFS with the underlying LIII EXAFS all data were compared to simulations to extract the undisturbed LII edge EXAFS information. Differences in electronic structure are visible in the near edge region (XANES). For an in situ evaporated Mo film on Si(100) we found a silicide reaction at room temperature resulting in a Mo-Si distance R = 0.249 nm and a coordination number N = 6.5. Both values are less than those of MoSi2 (R = 0.262 nm, N = 10). Using a native silicon oxide as a substrate the evaporated film is not of silicide like structure. The EXAFS of cosputtered MoSix (x = 2 − 3) layers, which showed no X-ray diffraction lines after deposition, reveal a short range order with a Mo-Si distance R = 0.256 nm and N = 6.5. There is no evidence of metal clusters in these amorphous layers. Annealing at about 1000 K for 3 min leads to the formation of a local MoSi2 structure.