- Email: [email protected]
Theoretical studies of molecules adsorbed on solid surfaces
A427 • Surface Science 134 (1983) 601-613 North-Holland Publishing Company
601
ON THE GENERATION OF TRIAL STRUCTURES AND THE EVALUATION OF THE FORMATION ENERGY FOR LAYERS OF CHEMISORBED MOLECULES ON METAL SURFACES: NAPHTHALENE AND AZULENE ON Rh(111) A. GAVEZZOTTI
and M. SIMONETTA
Dipartimento di Chimica Fisica ed Elettrochimica e Centro CNR, Universitd di Milano, 1-20133 Milano, ltaly Received 4 July 1983; accepted for publication 22 August 1983 We describe a simple method to generate a number of plausible trial structures for layers of chemisorbed molecules on metal surfaces, based on symmetry arguments. The formation, or packing, energy of these layers can be evaluated as sums of non-bonded interactions, and their stability can be judged on the basis of the shape of the packing energy profile as a function of molecular rotation. For naphthalene and azulene on Rh(111), p3 and pgg (or pg) structures are found to be the most stable. The definition and possible appearance of "twinned" layer structures is discussed. The method is claimed to provide inexpensive and reliable structural information for layers of large covalent molecules.
614
Surface Science 134 (1983) 614-638 North-Holland Publishing Company
THEORETICAL STUDIES SURFACES I. E l e c t r o n i c s p e c t r a H. KONO,
OF
MOLECULES
ADSORBED
ON
SOLID
A . R . Z I V * a n d S.H. L I N
Department of Chemistry, Arizona State University, Tempe, Arizona 85287, USA Received 17 May 1983; accepted for publication 23 August 1983 The band shape of electronic spectra for a diatomic molecule adsorbed on a surface is studied using the adiabatic approximation. In this approximation, the Schr~linger equation for the total system is separated into those for electronic motion, intramolecular vibration, and low frequency motions (e.g., hindered molecular rotation and lattice vibration). Our theory is applied to the system of an admolecule on the (001) surface of fcc monatomic crystals. We determine the line shape of a vibronic transition for both chemisorption and physisorption cases. In chemisorption cases, a side band due to the low frequency motions can appear in the line shape of a vibronic transition. On the other hand, in physisorption cases, the line shape is a single peak. Moreover, we suggest theoretically a new experimental technique for exciting adsorbed molecules; for this purpose, we derive equations giving the cross sections for the electronic excitation of admolecules by using ion impact at grazing incidence. The admolecules can be excited by this method; the subsequent light emission can give information on the orientation of the admolecule on the surface and on the admolecule-surface species interaction.
601
ON THE GENERATION OF TRIAL STRUCTURES AND THE EVALUATION OF THE FORMATION ENERGY FOR LAYERS OF CHEMISORBED MOLECULES ON METAL SURFACES: NAPHTHALENE AND AZULENE ON Rh(111) A. GAVEZZOTTI
and M. SIMONETTA
Dipartimento di Chimica Fisica ed Elettrochimica e Centro CNR, Universitd di Milano, 1-20133 Milano, ltaly Received 4 July 1983; accepted for publication 22 August 1983 We describe a simple method to generate a number of plausible trial structures for layers of chemisorbed molecules on metal surfaces, based on symmetry arguments. The formation, or packing, energy of these layers can be evaluated as sums of non-bonded interactions, and their stability can be judged on the basis of the shape of the packing energy profile as a function of molecular rotation. For naphthalene and azulene on Rh(111), p3 and pgg (or pg) structures are found to be the most stable. The definition and possible appearance of "twinned" layer structures is discussed. The method is claimed to provide inexpensive and reliable structural information for layers of large covalent molecules.
614
Surface Science 134 (1983) 614-638 North-Holland Publishing Company
THEORETICAL STUDIES SURFACES I. E l e c t r o n i c s p e c t r a H. KONO,
OF
MOLECULES
ADSORBED
ON
SOLID
A . R . Z I V * a n d S.H. L I N
Department of Chemistry, Arizona State University, Tempe, Arizona 85287, USA Received 17 May 1983; accepted for publication 23 August 1983 The band shape of electronic spectra for a diatomic molecule adsorbed on a surface is studied using the adiabatic approximation. In this approximation, the Schr~linger equation for the total system is separated into those for electronic motion, intramolecular vibration, and low frequency motions (e.g., hindered molecular rotation and lattice vibration). Our theory is applied to the system of an admolecule on the (001) surface of fcc monatomic crystals. We determine the line shape of a vibronic transition for both chemisorption and physisorption cases. In chemisorption cases, a side band due to the low frequency motions can appear in the line shape of a vibronic transition. On the other hand, in physisorption cases, the line shape is a single peak. Moreover, we suggest theoretically a new experimental technique for exciting adsorbed molecules; for this purpose, we derive equations giving the cross sections for the electronic excitation of admolecules by using ion impact at grazing incidence. The admolecules can be excited by this method; the subsequent light emission can give information on the orientation of the admolecule on the surface and on the admolecule-surface species interaction.