ELECTRONIC SPECTROSCOPY OF CARBON CHAINS OF ASTROPHYSICAL RELEVANCE

Maier, John P.

ELECTRONIC SPECTROSCOPY OF CARBON CHAINS OF ASTROPHYSICAL RELEVANCE

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Date

2011

Authors

Maier, John P.

Publisher

Ohio State University

Abstract

Electronic spectra of radicals and ions containing carbon chain skeleton are measured in the laboratory using a number of spectroscopic techniques. The species are selected because of their astrophysical relevance: possessing allowed electronic transitions in the optical range, where absorption measurements through diffuse interstellar clouds have been made. Initial survey spectra are obtained by observation of the absorption of mass-selected species in 6 K neon matrices. Examples of this are the detections of the electronic transitions of protonated coronene and C $7$ H $7+$ isomers. This information is then used to search for the relevant transitions in the gas phase using a number of sensitive laser techniques. In the gas phase the species are produced at low temperatures, 20$- $80 K, u s i n g s l i t j e t s u p e r s o n i c e x p a n s i o n s t h r o u g h w h i c h a d i s c h a r g e r u n s . T h e a b s o r p t i o n s a r e d e t e c t e d b y c a v i t y r i n g − d o w n a n d d e g e n e r a t e f o u r w a v e m i x i n g m e t h o d s; t h e l a t t e r a p p r o a c h p r o v i d i n g c e r t a i n a d v a n t a g e s . U s i n g a t w o c o l o r d e g e n e r a t e f o u r w a v e a p p r o a c h b o t h d o u b l e r e s o n a n c e l a b e l i n g o f r o t a t i o n a l l e v e l s a n d m a p p i n g o f t h e g r o u n d s t a t e v i b r a t i o n a l m a n i f o l d i s a c h i e v e d, s u c h a s f o r C$ _4 $H, X$ ^2\Sigma^+ $. U s i n g a c o m b i n a t i o n o f t h e a b o v e t e c h n i q u e s t h e e l e c t r o n i c t r a n s i t i o n s o f H$ 2 $C C C c o u l d b e i d e n t i f i e d i n t h e g a s p h a s e a n d t h e s e m a t c h w i t h t w o b r o a d d i f f u s e i n t e r s t e l l a r b a n d s, i m p l y i n g t h e f i r s t i d e n t i f i c a t i o n o f s u c h a c a r r i e r . E l e c t r o n i c a b s o r p t i o n s o f m a s s − s e l e c t e d c a t i o n s c o n s t r a i n e d i n a 22− p o l e r a d i o − f r e q u e n c y t r a p a r e m e a s u r e d . T h e v i b r a t i o n a l a n d r o t a t i o n a l d e g r e e s o f f r e e d o m a r e e q u i l i b r a t e d t o a r o u n d 20 K b y c o l l i s i o n s w i t h c r y o g e n i c a l l y c o o l e d h e l i u m . T h e t r a n s i t i o n o f t h e i o n i s t h e n d e t e c t e d b y a t w o c o l o r e x c i t a t i o n$ - $d i s s o c i a t i o n s c h e m e . E x a m p l e s o f t h i s a r e p o l y a c e t y l e n e c a t i o n s, r e v e a l i n g t h a t n o t o n l y t h e l o w e s t e n e r g y t r a n s i t i o n s b u t h i g h e r o n e s a r e o f r e l e v a n c e t o a s t r o n o m i c a l o b s e r v a t i o n s . T h e s p e c t r a a r e a l s o w i t h o u t o v e r l a p p i n g f e a t u r e s o f o t h e r s p e c i e s a s i s e n c o u n t e r e d i n t h e m e a s u r e m e n t s t h r o u g h d i s c h a r g e p l a s m a s . C o m p a r i s o n o f t h e s p e c t r o s c o p i c d a t a o n H C$ {2n} $H$ ^{+}$ $n$ =2,3 cations with astronomical measurements indicates that magnetic dipole transitions and velocity broadenings in the astronomical data have to be considered.

Description

Author Institution: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland

URI

http://hdl.handle.net/1811/49644

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Abstracts of OSU International Symposium on Molecular Spectroscopy 2010-2013

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