A. Giardini-Guidoni

ENERGETICS OF MOLECULAR COMPLEXES IN A SUPERSONIC BEAM : A NOVEL SPECTROSCOPIC TOOL FOR ENANTIOMERIC DISCRIMINATION

A subtle balance between attractive (electrostatic and dispersive) and repulsive (steric) forces is responsible for the different stabilities and spectral features of supersonically expanded van der Waals complexes between (R)-(+)-1-phenyl-1-propanol (R) and (R)-(−)- (r) or (S)-(+)-2-butanol (s). The homochiral Rr complex is more stable than the heterochiral Rs diastereomer in both the ground and excited states (see drawing). This was determined by the first direct measurement of the binding energies of the diastereomeric complexes by two color resonance two photon ionization/time-of-flight mass spectrometry.

Characterization of the plasma plume and of thin film epitaxially produced during laser ablation of SnSe

Abstract Laser-induced ablation was applied to thin film deposition from a tin selenide target. Diagnostic methods are applied to the characterization of the laser ablated plume. Emission from atomic and ionic excited states of tin and selenium dominates the total emission of the plasma plume with excitation temperatures up to 12 000 K. A high-speed ICCD camera has also been used to study three-dimensional plume propagation. Positive and negative cluster ions of bare tin, selenium and of the combined elements have been detected by laser mass-spectrometry of the plume. The growth of SnSe has been analysed by electrical and optical techniques. The effect of laser fluence on the plume and on the properties of the deposits has also been studied. The epitaxial growth of SnSe on several substrates is reported.

The measured auger electron spectrum of ammonia vapour

Abstract The electron excited Augere mission spectrum of ammonia vapour has been recorded at various scattering angles and analyzed. Previously calculated intensity and energy of the Auger transitions are compared with the observed spectrum and found in fair agreement.

Spectroscopic enantiodifferentiation of chiral molecules in the gas phase

Enantiodiscrimination of several chiral molecules, i.e. S-(+)- (s) vs R-(−)-2-butanol (r) and S-(+)- (s′) vs R-(−)-2-butylamine (r′), is obtained by two-color resonance-enhanced two-photon ionization time-of-flight (2cR2PI-TOF) spectroscopy of their supersonically expanded complexes with a suitable chromophore, i.e. R-(+)-1-phenyl-1-propanol (R). Analysis of the 2cR2PI-TOF excitation spectra indicates that these complexes are formed in the supersonic beam in several isomeric hydrogen-bonded structures. The different batochromic shifts of the band origin regions of the molecular diastereomeric complexes relative to that of bare R provide a viable means for spectroscopically discriminating the enantiomers. A further tool for their differentiation is provided by the very reproducible differences in the mass spectral fragmentation patterns of the jet-cooled diastereomeric aggregates. Chirality 11:376–380, 1999.

Observation of structure in the quasicontinuum of multiple-photon-excited C2 F5Cl

Abstract We report the observation of strong spectral structure in the dissociation yield of C 2 F 5 Cl excited by two CO 2 lasers, as a function of the second, non-resonant laser, observed under molecular-beam conditions. This structure is associated with combination bands revealed by matrix-isolation spectroscopy.

Satellite structures and momentum distributions in binary (e, 2e) spectroscopy of N2O

Abstract The (e, 2e) coincidence technique has been applied in studying the valence shell of N2O. The assignment of some satellite structures is discussed.

Composition and gas dynamics of laser ablated AlN plumes

Abstract The formation, composition and propagation of pulsed laser produced plasma plumes from an AlN target have been studied in real time by spatially and temporally resolved optical spectroscopy. The mean front velocity has been measured and appears to be slightly slower in the presence of added gas than in vacuum. In the initial stage of expansion, this velocity is almost the same for all neutral particles in the plume in the initial stage of expansion. Velocities of neutral and ionic species have been measured by their time of arrival from the target to a quadrupole mass spectrometer and their expansion beam Maxwell-Boltzmann (MB) temperature determined. The plume electronic temperature has been determined by assuming a local thermodynamic equilibrium of the emitting species.

Spectroscopy of 4-fluorostyrene clusters

Abstract The R2PI mass spectra of jet cooled 4-fluorostyrene (4-FSTY) pure or mixed with various atoms and compounds such as Ar, Kr, N 2 , C 2 H 5 , NH 2 , CCl 4 show the presence of eterogeneous cluster ions. The wavelength spectra of these clusters show specific shift of the O 0 0 band due to vdW interactions.

Laser induced ablation and epitaxial growth of SnSe

Abstract The ablation technique was applied to thin film deposition from SnSe powders. A mechanism for epitaxial growth as characterized by X-rays and scanning electron microscope analysis is suggested. Plume analysis of the ablated material is also reported.

Ionization potentials and electron momentum distributions for SiF4 valence-shell orbitals: an (e,2e) spectroscopic investigation and Green's function study

Abstract Ionization potentials and electron momentum distributions of SiF 4 valence-shell orbitals have been measured by means of (e,2e) spectroscopy. SCF calculations and a Greens function study have been performed on the same molecule. A comparison between experimental and theoretical results shows that a significant interaction of 2p F with 3d Si orbitals occurs.