AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP4
The Adsorption-Desorption Properties of CO on W(111) Surface

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: S.-B. Lee, SungKyunKwan University, Korea
Authors: S.-B. Lee, SungKyunKwan University, Korea
S.-Y. Lee, SungKyunKwan University, Korea
Y.-D. Kim, SungKyunKwan University, Korea
T.S. Yang, SungKyunKwan University, Korea
J.-H. Boo, SungKyunKwan University, Korea
C.Y. Park, SungKyunKwan University, Korea
H.-T. Kwak, Kook Min University, Korea
Correspondent: Click to Email
The adsorption and desorption properties of CO have been studied on W(111) surface in the temperature range of 300 - 1100 K by LEED, XPS, UPS, and TDS. After CO saturation at 300 K, four adsorption states obtained from TDS experiment were observed at 400, 850, 1000, and 1100 K, called @alpha@, @beta@@sub 1@, @beta@@sub 2@, and @beta@@sub 3@ states, respectively. The desorption temperature of @beta@@sub 3@-CO state shifted to higher temperature with increasing CO exposure signifying an attractive lateral interaction between adsorbed species. Using Bragg-Williams approximation the lateral interaction energy (-5.7 kJ/mol) was calculated and the TD-spectra obtained experimentally were successfully simulated using by quasi-chemical approximation. The desorption kinetic order of the @beta@@sub 3@-CO state is followed by the first order indicating that the adsorbed state of @beta@@sub 3@-CO seems to be a molecular state rather than that of dissociated state. With UPS and XPS, the CO adsorption property (especially the @beta@@sub 3@-CO) on W(111) was clearly confirmed. The adsorption of CO on W(111) at 300 K exhibited only one emission peak at -6.3 eV below Fermi level due to 1@pi@+5@sigma@ molecular orbitals of CO. With heating the adsorbed CO to 1000 K, however, an additional emission peak was also observed at -7.1 eV due to an orbital energy splitting of 1@pi@+5@sigma@. This is strongly supported with a theoretical result calculated by ASED-MO method. Comparing the O state of @beta@@sub 3@-CO with that obtained from the dissociatively adsorbed oxygen species, we can identify that the @beta@@sub 3@-CO is different with that for dissociated CO suggesting a non-dissociated CO species with different geometry. From these results, a lying-down species of adsorbed CO is proposed.