DENVER, COLORADO 80210https://ntrs.nasa.gov/search.jsp?R=19690030688 2018-05-10T18:05:51+00:00Z
I o n i z a t i o n and i n Low-Energy S t a t e Me t a s t a b l e Exc i t a t i o n C o l l i s i o n s of GroundArgon A t o m s * 4 P a u l 0. Haugsjaa' and Robert C. Amme 1~~~-u 6 -0 0 + -~~6 * Supported i n p a r t by a g r a n t from t h e N a t i o n a l Aeronautics and Space Administration.
ABSTRACTA low-energy beam of argon atoms, formed by non-resonant charge t r a n s f e r of Ar' i n H has been used t o explore the nearthreshold behavior f o r i o n i z i n g and e x c i t i n g c o l l i s i o n s between argon atoms. For excess center-of-mass e n e r g i e s below 12 e V , the i o n i z a t i o n d a t a a r e c o n s i s t e n t with the e m p i r i c a l r e l a t i o n s h i p CT-w1.8 x i n e l e c t r o n -v o l t s .were used i n an e f f o r t t o observe metastable atoms formed i n atom-
atom c o l l i s i o n s by Penning i o n i z a t i o n . I n t h i s c a s e , beam e n e r g i e s were r e s t r i c t e d t o v a l u e s l e s s than 30 eV t o avoid d i r e c t i o n i z a t i o nof the a c e t y l e n e (Penning) gas by the ground-state atom beam. A t 2'(~-1 5 . 8 ) "~, where E i s t h e c e n t e r of mass energy Target
* + C2H22 INTRODUCTION 1 I n 1957, Petschek and Byron proposed t h a t t h e i n i t i a l i o n i z a t i o n of shock-heated argon proceeds v i a a two-s t e p process.The f i r s t s t e p i s considered t o be t h e e x c i t a t i o n of argon by atom-atom c o l l i s i o n s , A r + A r 4 A r + Ar*. The second s t e p i s presumably t h e c o l l i s i o n between an e x c i t e d atom and a n o t h e r atom, A r + A r -, A r + Ar' + e -, which produces t h e f i r s t e l e c t r o n s i n t h e bulk i o n i z a t i o n process.
*An a c t i v a t i o n energy f o r t h e e x c i t a t i o n s t e p has been r e p o r t e d by s e v e r a l i n v e s t i g a t o r s t o b r a c k e t t h e f i r s t f o u r e x c i t e d s t a t e s of t h e argon atom. 2-4 from t h e 3p 4s e l e c t r o n c~n f i g u r a t i o n .~ a t 11.55 and 11.72 eV, a r e m e t a s t a b l e and t h e o t h e r s , a t 11.62 and 11.83 eV, a r e n o t .These e x c i t e d s t a t e s a r i s e 5 Two of the s t a t e s , thoseSince i t was n o t known t o what e x t e n t t h e e x c i t a t i o n of m e t a s t a b l e l e v e l s i s r e s p o n s i b l e f o r t h e r a t e -c o n t r o l l i n g s t e p t o a n e x c i t e d s t a t e , atomic beam measurements of t h e c r o s s s e c t i o n very n e a r t h e i o n i z a t i o n t h r e s h o l d . This l a t t e r c r o s s s e c t i o n g i v e s information about t h e energy dependence of t h e c r o s s s e c t i o n f o r t h e second s t e p i n t h e i n i t i a l i o n i z a t i o n p r o c e s s , 02, s i n c e t h e s e two c r o s s s e c t i o n s , 0-and 02, a r e expected t o have e s s e n t i a l l y the same t h r e s h o l d behavior6 when compared i n terms of t h e excess energy Ee a v a i l a b l e i n the center-of...
Trivalent cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, thulium, and ytterbium electroluminesce in liquid phosphorus oxychloride solutions at room temperature. Trivalent terbium electroluminesces also in dimethyl sulfoxide and propylene carbonate. The emission is due to the known inner "f" subshell transitions of the trivalent ions, originating from established metastable states. The electrolu~inescence spectra of the ions range from the ultraviolet (in the case of Gd H ) , through the visible (Ce 3 +, Pr H , SmH, Eu H , Tb H , DyH, and TmH), to the infrared (Nd 3 +, Yb H ). The emission originates at the surface of the negative electrode and becomes observable, in the case of green emitting Tb 3 +, at about 6 V dc. The electroluminescence is explained by the following mechanism: Application of an external potential attracts the Helmholtz and Gouy Chapman layers of solvated cations towards the surface of the cathode. This causes a Schottky lowering of the barrier to electron escape and allows electrons to escape from the cathode into the electrode/electrolyte interface. The electrons are accelerated across the positive ion rich interface and acquire enough energy to excite the luminescent cations by inelastic collisions.
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