Low energy electron vibrational excitation of molecules adsorbed on surfaces: experiment and theory

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1979

OSTI ID:5401250

Ho, W

The phenomena of interest occurs at the interface between adsorbed molecules and transition metal surfaces. Of particular importance is the identification of the chemical species and the determination of the molecular structures. The experiments were done under ultrahigh vacuum, typically approx. 1.5 x 10/sup -10/ torr. A specified amount of the desired molecules are let into the vacuum systems and allowed to adsorb on the surface. A beam of low energy (<30 eV) electrons is incident on the surface and the scattered electrons are energy analyzed. Some of the electrons scatter inelastically, typically 1 part in a thousand, due to vibrational excitation of the adsorbed molecules. The characteristic discrete energy losses reflect the particular chemical bonds of the adsorbed species on the surface. As in conventional infrared absorption and Raman scattering spectroscopies, chemical identification and molecular structural determination are possible by analyzing the vibrational frequencies and intensities. The sensitivity for detecting the adsorbed species is approx. 0.01 fractional coverage of the surface. Since vibrational energies are approx. 100 MeV, a monochromatic beam of electrons having an energy width 30 MeV is necessary. A spectrometer consisting of the monochromator and the analyzer was designed and built. The basic vibrational excitation mechanisms were concentrated on first. For the first time, new vibrational modes away from the specular direction were observed and a detailed study of the impact energy dependence of the vibrational excitation cross sections were made.

• Research Organization: Pennsylvania Univ., Philadelphia (USA)
• OSTI ID: 5401250
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular &amp; Chemical Physics-- Beams &amp; their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION
ABSORPTION SPECTROSCOPY
BEAMS
CHEMICAL BONDS
COLLISIONS
ELECTRON BEAMS
ELECTRON COLLISIONS
ELEMENTS
ENERGY LOSSES
ENERGY-LEVEL TRANSITIONS
EXCITATION
INELASTIC SCATTERING
LEPTON BEAMS
LOSSES
METALS
MOLECULAR STRUCTURE
MOLECULES
PARTICLE BEAMS
SCATTERING
SPECTROSCOPY
SURFACES
TRANSITION ELEMENTS
ULTRAHIGH VACUUM