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Chemical reactivity of (010)MoO3: A structural study of the MoO2 formation in molecular hydrogen
A450 where the unit mesh contains 12 adatoms or atom clusters in a locally [2 x 2l arrangement, and "trianglc-dimcr'" models where the unit mesh contains 9 dimers or pairs of dimers bordering a triangular suhunit of the unit mesh. The distribution of diffraction intensity among fractional-order spots is calculated kinematically and compared with TEl) patterns observed by Petroff and Wilson and others. No agreement is found for adatom models. Good but not perfect agrcemcnt is found for one triangle-direct model.
396
Surface Science 147 (1984) 396- 412 North-Holland, Amsterdam
CHEMICAL REACTIVITY OF (010)MOO3: A S T R U C T U R A L STUDY OF THE M o O 2 FORMATION IN MOLECULAR HYDROGEN L.C. DUFOUR,
O. BERTRAND
and N. FLOQUET
Lahoratoire de Reeherches sur la RbactivitO des Solides. LA 23 CNRS, Facultb des Sciences Mirande, BP 138, F-21004 Dijon Cedex. France Received 28 March 1984: accepted for publication 31 July 1984 The reduction of (010)MOO 3 in molecular hydrogen under low pressure (3× 10 ) Pal was investigated between 300 and 720 K by Reflection High Energy Electron Diffraction and Auger Electron Spectrometry. A three-dimensional MoO 2 structure was found to be directly formed from MoO> MoO 2 nucleation took place through some MoO, crystallographic planes having the same MoO 6 octahedra arrangement as in the MOO3(010) plane. It is deduced that the mechanism of the transformation strongly depends on the layered structure of MoO 3. This transformation might be initiated by a periodic defect detected along the MOO3[101 ] directions. Some modifications of properties of the MoO3(010 ) plane as induced by heating are also presented.
Surface Science 147 (1984) 413-426 North-Holland, Amsterdam
MINDO/3
413
S T U D Y OF PERIODIC OVERLAYERS ON GRAPHITE
J.M. RICART
a n d J. V I R G I L I
Departamento de Ouimica*Fisica, Fac. Quirnica, Universitat de Barcelona, Acgda, Diagonal 647, 08028 Barcelona, Spain and F. I L L A S
Deparlamento de Quimica-Fisica, Fac. Quimica de Tarragona, Unicersitat de Barcelona, Pq'a. Imperial Tarraco s / n . 43005 Turragona, Spain Received 24 May 1984: accepted for publication 26 July 1984 The crystalline orbital M 1 N D O / 3 method has been applied to the study of regular phases of H, C, N, and O chemisorbed on graphite. Results for regular phases of H are comparable to ab-initio band calculations. While band structures are similar topologically to available C N D O / 2 data, the M 1 N D O / 3 method overcomes the main deficiencies of C N D O / 2 and EHT approaches, not needing either the introduction of scale factors on the calculated energies or the manipulations on the parametrization. For atomic H, C and N phases, the stablest one corresponds to a 1:1 composition, while for atomic O it corresponds to a 1 : 2 surface composition. The band structure of each one of the stablest phases is discussed and the results are compared with previous M I N D O / 3 cluster model calculations.
396
Surface Science 147 (1984) 396- 412 North-Holland, Amsterdam
CHEMICAL REACTIVITY OF (010)MOO3: A S T R U C T U R A L STUDY OF THE M o O 2 FORMATION IN MOLECULAR HYDROGEN L.C. DUFOUR,
O. BERTRAND
and N. FLOQUET
Lahoratoire de Reeherches sur la RbactivitO des Solides. LA 23 CNRS, Facultb des Sciences Mirande, BP 138, F-21004 Dijon Cedex. France Received 28 March 1984: accepted for publication 31 July 1984 The reduction of (010)MOO 3 in molecular hydrogen under low pressure (3× 10 ) Pal was investigated between 300 and 720 K by Reflection High Energy Electron Diffraction and Auger Electron Spectrometry. A three-dimensional MoO 2 structure was found to be directly formed from MoO> MoO 2 nucleation took place through some MoO, crystallographic planes having the same MoO 6 octahedra arrangement as in the MOO3(010) plane. It is deduced that the mechanism of the transformation strongly depends on the layered structure of MoO 3. This transformation might be initiated by a periodic defect detected along the MOO3[101 ] directions. Some modifications of properties of the MoO3(010 ) plane as induced by heating are also presented.
Surface Science 147 (1984) 413-426 North-Holland, Amsterdam
MINDO/3
413
S T U D Y OF PERIODIC OVERLAYERS ON GRAPHITE
J.M. RICART
a n d J. V I R G I L I
Departamento de Ouimica*Fisica, Fac. Quirnica, Universitat de Barcelona, Acgda, Diagonal 647, 08028 Barcelona, Spain and F. I L L A S
Deparlamento de Quimica-Fisica, Fac. Quimica de Tarragona, Unicersitat de Barcelona, Pq'a. Imperial Tarraco s / n . 43005 Turragona, Spain Received 24 May 1984: accepted for publication 26 July 1984 The crystalline orbital M 1 N D O / 3 method has been applied to the study of regular phases of H, C, N, and O chemisorbed on graphite. Results for regular phases of H are comparable to ab-initio band calculations. While band structures are similar topologically to available C N D O / 2 data, the M 1 N D O / 3 method overcomes the main deficiencies of C N D O / 2 and EHT approaches, not needing either the introduction of scale factors on the calculated energies or the manipulations on the parametrization. For atomic H, C and N phases, the stablest one corresponds to a 1:1 composition, while for atomic O it corresponds to a 1 : 2 surface composition. The band structure of each one of the stablest phases is discussed and the results are compared with previous M I N D O / 3 cluster model calculations.