Synthesis and Placental Binding Potencies of Photosensitive Analogues of Luteinizing Hormone Releasing Hormone (LHRH) with Agonistic and Antagonistic Structures

The synthesis of new photolabeling analogues of luteinizing hormone releasing hormone is described. Peptides were prepared by the solid-phase method, and the photolabeling moiety was introduced as the 4′-nitrophenyl-alanine precursor. This amino acid, either of the L or D configuration, was placed at different positions and was modified afterwards to 4′-azidophenylalanine. Structures with agonistic or antagonistic character were prepared, together with a peptide containing simultaneously the photolabeling moiety and a biotin substituent for future receptor isolations. Binding studies on placental and pituitary membranes indicate that these compounds represent promising candidates for receptor labeling studies.     

Pure rotational spectrum of PH3 in the 10–100 cm−1 range: Collisional broadening coefficients by H2 and He

The H₂- and He-broadened widths have been measured at room temperature for seven pure rotational lines of phosphine in the spectral range 10–80 cm^–1. The retrieval of linewidths values was carried out, on the assumption of identical linewidths for theJ+1K-components within a given multipletJ+1J. The results obtained are in good agreement with the previous determination reported for the 10 line, in the microwave range.     

Long-lived excited states at surfaces: Cs/Cu(111) and Cs/Cu(100) systems

One-electron and multielectron contributions to the decay of transient states in the Cs/Cu(111) and (100) systems are studied by a joined wave-packet propagation and many-body metal response approach. The long lifetime of these states is due to the Cu L and X band gaps which reduce the electron tunneling between Cs and Cu. In the (111) case, the decay is mainly by inelastic e-e interaction, whereas in the (100) case, electron tunneling is dominating. This accounts very well for the experimental findings [Bauer et al., Phys. Rev. B 55, 10 040 (1997) and Ogawa et al., Phys. Rev. Lett. 82, 1931 (1999)].     

Laser-induced photo-desorption in the Na/Cu(1 1 1) system

Desorption in the Na/Cu(1 1 1) system induced by an electronic excitation is studied using a quantal approach. The system is excited by a laser pulse in the fs range to the Na¹ state corresponding to the transient capture of an electron by the alkali adsorbate. The present quantal approach describes on an equal footing the laser-induced vibrational excitation of the adsorbate in the adsorption well and the photo-desorption process. It confirms earlier results using a semi-classical input. It also allows a discussion of the photo-desorption probability with the photon energy: the maximum of the desorption probability per absorbed photon occurs off-resonance in the high-energy wing of the electronic transition. This feature is related to the dynamics of the laser-induced process.     

Stabilisation of alkali-adsorbate-induced states on Cu(111) surfaces

The Li and Cs alkali-adsorbate-induced states on a model Cu(111) surface are studied theoretically using the coupled angular mode and the wave packet propagation methods. Their energy position and their decay rate via one-electron transfer into the metal are calculated. An unoccupied alkali-induced state is found with a rather long lifetime, much longer than those found in the case of free-electron metal surfaces. This is attributed to the combined effect of the hybridisation of the alkali levels and of the Cu(111) projected band gap along the normal to the surface that blocks the electron transfer between the adsorbate and the metal. This qualitatively explains the experimental finding of a long-lived state by Bauer et al. [Phys. Rev. B 55 (1997) 10 040] and Ogawa et al. [Phys. Rev. Lett. 82 (1999) 1931].     

Scattering of Cu(1 0 0) image state electrons from single Cu adatoms and vacancies: A comparative study

A theoretical study of the electron dynamics in image potential states on Cu(1 0 0) surfaces with different types of defects (Cu adatoms and Cu vacancies) is presented for low defect density at the surface. A wave packet propagation approach is employed for the electron scattering calculations, where the defect induced potentials are obtained from an ab initio density functional study. Scattering of the image state electron by a defect induces inter-band and intra-band transitions leading, respectively, to the population decay and to the dephasing of the image states. Comparison of the respective effects of adatoms and vacancies shows that Cu adatoms are much more efficient in inducing population decay and dephasing of the image potential states. Present results for the case of Cu adatoms are compared with available time-resolved two-photon photoemission data.     

Role of the 2D surface state continuum and projected band gap in charge transfer in front of a Cu(111) surface

Electron capture by Li+ and H projectiles in grazing scattering from Cu(111) and Cu(110) surfaces is studied experimentally and theoretically. Whereas data for Cu(110) can be described by established theoretical methods treating resonant charge transfer with a free-electron metal, data for Cu(111) show pronounced deviations from this approach. We interpret our observations by the effect of the projected L-band gap of the Cu(111) surface. In particular, the quantum states of reduced dimension (2D surface state continuum) play a dominant role in electron transfer.