m o l e c u l a r beam, measur ed by a b o l o m e t e r , a s a f u n c t i o n o f l a s e r f r e q u e n c y f o r a r a n g e of d i f f e r e n t beam c o n d i t i o n s .

F i g u r e 3 . 8 i n d i c a t e s t h a t as t h e w a t e r c o n c e n t r a t i o n i s r e d u c e d , t h e b r o a d f e a t u r e r e m i n i s c e n t of t h e s p e c t r u m of l i q u i d w a t e r ( R o b e r t s o n and W i l l i a m s ( 1 9 7 1 ) ) , t hou gh s h i f t e d t o t h e b l u e by a bo u t a h u n d r e d wave numbers , g i v e s way t o s e v e r a l s t r o n g f e a t u r e s which emerge from -the e n v e l o p e . Ther e i s a l s o e v i d e n c e of a s m a l l band which p e r s i s t s i n t h e low f r e q u e n c y t a i l n e a r 3200 cm- "1. The s h a r p band above 3700 cm“ 1 i s e v i d e n t i n a l l s p e c t r a and grows i n r e l a t i v e i n t e n s i t y as t h e c o n c e n t r a t i o n i s r e d u c e d . T h i s band c o n s i s t s of a t l e a s t two d i s t i n c t p e a k s . F i g u r e 3 . 9 shows t h a t a t l e a s t s i x s t r o n g f e a t u r e s a r e a p p a r e n t i n t h e s p e c t r u m a t v e r y low c o n c e n t r a t i o n s and t h a t t h e weak band a t n e a r 3200 cm“ 1 i s p o s s i b l y r e s o l v e d i n t o two p e a k s . E x a m i n a t i o n o f t h e p r e s s u r e depen de n ce of t h e s e a b s o r p t i o n s , t o g e t h e r w i t h mass s p e c t r o m e t r y , i n d i c a t e s t h a t t h e s e low c o n c e n t r a t i o n s p e c t r a a r e most l i k e l y a s s o c i a t e d w i t h t h e w a t e r dimer and t r i m e r . F i g u r e 3-10 compares t h e e x p e r i m e n t a l r e s u l t s w i t h t h e v a l u e s o b t a i n e d from t h e random walk p r o j e c t i o n me thod. The v a l u e s a r e i n v e r y c l o s e a g r e e m e n t .

In document The quantum Monte Carlo method : application to problems in statistical physics (Page 123-125)