Zlatko Bacic

Department of Chemistry, New York University, New York, New York 10003, USA

We will present our computational methodology for exact quantum 6D diatomic molecule adsorbed on a rigid corrugated surface. It is aimed at adsorbates executing coupled, strongly anharmonic large-amplitude vibrations. Surface nonrigidity is introduced in an approximate way, by means of a simplified surface-mass model. With this methodology, we have calculated excited vibrational levels of CO molecule adsorbed on Cu(100) surface, for all four isotopomers of CO, using the empirical potential by Tully and co-workers. Our calculated fundamental frequencies of CO/Cu(100) vibrations are in good overall agreement with the experimental frequencies
and isotope frequency shifts; an important exception is the CO stretch fundamental. Comparison between the 6D results and those of 5D (rigid CO) and 4D (fixed-site) quantum calculations provide quantitative information about the couplings among the vibrational modes of CO on Cu(100).  Excited states of the lowest-frequency (doubly degenerate) frustrated translation mode are analyzed and assigned. Extension of this methodology to nonlinear polyatomic molecules will be discussed.