VIBRATIONAL COOLING OF LARGE MOLECULES IN SUPERSONIC EXPANSIONS: THE CASE OF C$_{60}$ AND PYRENE

Supersonic expansions are a useful tool for cooling molecules in the gas phase. While translational and rotational degrees of freedom can generally be cooled to low temperatures ($< $30 K) u s i n g t h i s t e c h n i q u e, t h e r e h a s b e e n c o n f l i c t i n g e v i d e n c e c o n c e r n i n g t h e c o o l i n g o f v i b r a t i o n a l d e g r e e s o f f r e e d o m . T h i s c o o l i n g i s p a r t i c u l a r l y i m p o r t a n t f o r g a s − p h a s e a b s o r p t i o n s p e c t r o s c o p y o f l a r g e m o l e c u l e s w i t h m a n y v i b r a t i o n a l d e g r e e s o f f r e e d o m, s u c h a s b u c k m i n s t e r f u l l e r e n e (C$ {60} $). W e h a v e a t t e m p t e d g a s − p h a s e i n f r a r e d s p e c t r o s c o p y o f C$ {60}$ by producing C $60$ vapor in a hot ($\sim $900 K) o v e n a n d s e e d i n g t h e v a p o r i n a n a r g o n s u p e r s o n i c e x p a n s i o n, b u t h a v e b e e n u n a b l e t o o b s e r v e a n y a b s o r p t i o n s i g n a l . W e a t t r i b u t e t h i s t o i n s u f f i c i e n t c o o l i n g o f v i b r a t i o n a l d e g r e e s o f f r e e d o m i n t h e e x p a n s i o n . I n c o n t r a s t, w e h a v e p e r f o r m e d a s i m i l a r e x p e r i m e n t w i t h p y r e n e (C$ {16} $H$ {10}$) heated to $\sim $430 K, w h i c h y i e l d e d r o t a t i o n a l l y − r e s o l v e d s p e c t r a a n d a n e s t i m a t e d v i b r a t i o n a l t e m p e r a t u r e o f 25−90 K . W e w i l l d i s c u s s t h e s e r e s u l t s a n d p o s s i b l e m e t h o d s t o o b t a i n g a s − p h a s e a b s o r p t i o n s p e c t r a o f C$ _{60}$.

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Author Institution: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

Brian E. Brumfield present address: Department of Electrical Engineering, Princeton University, Princeton, Nj 08544

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http://hdl.handle.net/1811/52258

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Abstracts of OSU International Symposium on Molecular Spectroscopy 2010-2013

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