Numerical calculations of gas-surface interactions.

Numerical calculations of gas-surface interactions a t e p ithermal energies are r e p o r t e d a n d c o r r e l a t e d .These i n t e r a c t i o n s , w h i c h i n v o l v e : t h e e f f e c t s o f d i f f e r e n t l a t t i c e s t r u c t u r e s and orientations, adsorbed contaminants, and lattice thermal motion, are compared a g a i n s t t h o s e of i d e a l FCC (100) s u r f a c e s a t 0 ° K .An analysis of energy exchange in 153 d i f f e r e n t s i t u a t i o n s ( i ncluding some previously reported) i s developed by considering a h i g h l y i d e a l i z e d model o f t h e i n t e r a c t i o n and determining parameters i n t h e model from the complete set of n u m e r i c a l r e s u l t s .The r e s u l t i n g s i m p l e e q u a t i o n c o r r e l a t e s t h e o r e t i c a l e n e r g y e x c h a n g e values with a s t a n d a r d d e v i a t i o n of about 10 p e r c e n t of t h e i n c id e n t e n e r g y f o r c o l d i d e a l s u r f a c e s , and about 20 p e r c e n t f o r h o t , c o n t a m i n a t e d s u r f a c e s a n d d i f f e r e n t s t r u c t u r e s .C h A previous report (Ref.2) p r e s e n t s e v i d e n c e f o r n e g l e c t i n g .oupling between l a t t i c e o s c i l l a t o r s i n c a l c u l a t i o n s i n v o l v i n g .i g h g a s p a r t i c l e e n e r g y .The p r e s e n t r e s u l t s l e n d f u r t h e r supp o r t t o t h i s a p p r o x i m a t i o n .A s i n g l e monolayer of adsorbed mater i a l was found i n e f f e c t t o d o m i n a t e t h e i n t e r a c t i o n i n most cases, i s o l a t i n g t h e g a s p a r t i c l e from a l l but a small, long-range influence of the bulk.Calculations of l a t t i c e t h e r m a l e f f e c t s on t h e i n t e r a c t i o n s , a l t h o u g h s u b j e c t to e r r o r s due to small sample s i z e , i n d i c a t e t h a t t h i s e f f e c t c a n s a f e l y b e i g n o r e d a t h i g h i n c i d e n t energy.L a t t i c e s u r f a c e s t r u c t u r e and azimuth angle of incidence were found t o b e i m p o r t a n t o n l y i n t h e FCC (110) case, where the s u r f a c e i s q u i t e r o u g h a n d h i g h l y d i r e c t i o n a l .