Gas-Phase Photodissociation of Transition Metal Ion Complexes and

Chapter 10

Gas-Phase Photodissociation of Transition Metal Ion Complexes and Clusters 1

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 30, 2017 | http://pubs.acs.org Publication Date: November 23, 1987 | doi: 10.1021/bk-1987-0359.ch010

Robert L. Hettich and Ben S. Freiser Department of Chemistry, Purdue University, West Lafayette, IN 47907 H i g h l i g h t s are presented from our recent work on the p h o t o d i s s o c i a t i o n of three c a t e g o r i e s of t r a n s i t i o n metal ion s p e c i e s : (I) ML (L=ligand), (II) ML +, and MFe (M=3d metal). The r e s u l t s i n d i c a t e that these species absorb broadly i n the u l t r a v i o l e t and v i s i b l e s p e c t r a l regions. Because of t h i s broad absorption, p h o t o d i s s o c i a t i o n thresholds are a t t r i b u t e d to thermodynamic f a c t o r s and y i e l d absolute bond energies. Isomer d i f f e r e n t i a t i o n i s demonstrated by observing d i f f e r e n c e s i n cross s e c t i o n s , s p e c t r a l band p o s i t i o n s , and fragmentation pathways. I n t e r e s t i n g l y , product ions generated by p h o t o d i s s o c i a t i o n are found i n some cases to d i f f e r s i g n i f i c a n t l y from those produced by c o l l i s i o n - i n d u c e d d i s s o c i ation. S o p h i s t i c a t e d pulse techniques, which permit the multistep synthesis and i s o l a t i o n of a wide v a r i e t y of organometallic i o n s , together with the long ion storage times, make FTMS i d e a l l y suited for these s t u d i e s . +

+

2

Over t h e p a s t s e v e r a l y e a r s , t h e a r e a o f g a s - p h a s e t r a n s i t i o n m e t a l i o n c h e m i s t r y has been g a i n i n g i n c r e a s i n g a t t e n t i o n from t h e s c i e n t i f i c community [ 1 - 1 6 ] . I t s a p p e a l i s m a n i f o l d : f i r s t , i t has b r o a d i m p l i c a t i o n s t o a s p e c t r u m o f o t h e r a r e a s such as a t m o s p h e r i c chemistry, c o r r o s i o n chemistry, s o l u t i o n organometallic chemistry, and s u r f a c e c h e m i s t r y ; s e c o n d l y , an a r s e n a l o f gas phase t e c h n i q u e s a r e a v a i l a b l e to study the thermochemistry, k i n e t i c s , and mechanisms o f t h e s e " u n u s u a l " s p e c i e s i n t h e a b s e n c e o f s u c h c o m p l i c a t i o n s a s s o l v e n t and l i g a n d

Current address: Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, T N 37831

0097-6156/87/0359-0155506.00/0 © 1987 American Chemical Society

Buchanan; Fourier Transform Mass Spectrometry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

156

FOURIER TRANSFORM MASS SPECTROMETRY


e f f e c t s ; and, t h i r d l y , t h e h i g h l y c o n t r o l l e d n a t u r e o f t h e s e gas phase e x p e r i m e n t s p e r m i t s t h e s t u d y o f s p e c i f i c l i g a n d e f f e c t s and p r o v i d e s d a t a f o r d i r e c t c o m p a r i s o n t o t h e o r y , as new t h e o r e t i c a l t r e a t m e n t s emerge. How does t h e g a s - p h a s e c h e m i s t r y o f a b a r e and, therefore, highly c o o r d i n a t i v e l y unsaturated t r a n s i t i o n m e t a l i o n compare t o i t s s o l u t i o n c o u n t e r p a r t ? As a r e p r e s e n t a t i v e example, Beauchamp and c o w o r k e r s p r o p o s e d Scheme I f o r t h e d e h y d r o g e n a t i o n o f b u t a n e by N i [ 2 ] . The mechanism shown has a n a l o g i e s t o s o l u t i o n o r g a n o Scheme I

,

Y >

r

t

\

. > Λ

"

.

>

+

ll-Ni -||

•

H,

y/ m e t a l l i c c h e m i s t r y , but i s u n u s u a l i n t h a t o x i d a t i v e a d d i t i o n of the metal c a t i o n i s proposed t o occur at the C-C bond as opposed t o t h e C-H bond, w h i c h i s t h e e x a c t o p p o s i t e o f what i s g e n e r a l l y o b s e r v e d i n s o l u t i o n studies. O x i d a t i v e a d d i t i o n o f F e , C o , and N i t o C-C bonds i n l o n g e r c h a i n a l k a n e s a p p e a r s t o be g e n e r a l [ 3 - 7 ] . In o r d e r t o p r o p o s e a mechanism such as t h a t shown i n Scheme I, i t i s e v i d e n t t h a t not o n l y must t h e p r o d u c t i o n m a s s - t o - c h a r g e r a t i o ( e m p i r i c a l f o r m u l a ) be d e t e r m i n e d , but a l s o t h e s t r u c t u r e o f t h e i o n must be elucidated. C l e a r l y , a d i f f e r e n t mechanism i n v o l v i n g C-H i n s e r t i o n m i g h t have been p r o p o s e d i f t h e N i C . H p r o d u c t had been N i - b u t e n e i n s t e a d o f Ni(ethéne) . S e v e r a l e f f e c t i v e s t r u c t u r a l probes are a v a i l a b l e to the gas-phase i o n chemist i n c l u d i n g c o l l i s i o n - i n d u c e d d i s s o c i a t i o n [ 3 1 4 a , 4 b ] , i o n - m o l e c u l e r e a c t i o n s ( f o r metal i o n complexes, l i g a n d exchange [ 1 - 3 ] and H/D exchange [5] are commonly e m p l o y e d ) , and use o f s p e c i f i c a l l y l a b e l l e d n e u t r a l compounds [ 2 , 6 , 7 ] . E a c h o f t h e s e methods was a p p l i e d t o t h e r e a c t i o n shown i n Scheme I and c o n f i r m t h e presence of N i ( e t h e n e ) . Another important c o n s i d e r a t i o n i n f o r m u l a t i n g a mechanism i s w h e t h e r each s t e p , as w e l l as t h e o v e r a l l process, i s thermodynamically feasible. In Scheme I t h e f i r s t s t e p i n v o l v e s c l e a v i n g t h e c e n t r a l C-C bond and f o r m i n g two N i * - C bonds. Thus, t h e d e t e r m i n a t i o n of m e t a l - l i g a n d bond e n e r g i e s i s c r i t i c a l l y important. A g a i n , s e v e r a l p o w e r f u l g a s - p h a s e t e c h n i q u e s can be a p p l i e d to t h i s problem. Among t h e s e , t h e d e t e r m i n a t i o n o f e n d o t h e r m i c r e a c t i o n t h r e s h o l d s from ion-beam e x p e r i ments has y i e l d e d t h e m a j o r i t y o f t h e a b s o l u t e v a l u e s c u r r e n t l y i n t h e l i t e r a t u r e today [ 1 , 8 , 9 ] . Ligand d i s +

+

+

+

g

+

+

2

+

2



10.

HETTICH AND FREISER

Photodissociation of Transition Metal Ions

157

p l a c e m e n t r e a c t i o n s and e q u i l i b r i u m measurements have y i e l d e d a c c u r a t e r e l a t i v e m e t a l i o n - l i g a n d bond e n e r g i e s f o r a v a r i e t y o f m e t a l c a t i o n s and l i g a n d s [10,11]. Observation of exothermic i o n - molecule r e a c t i o n s can p r o v i d e l i m i t s on t h e s e e n e r g i e s and, most r e c e n t l y , c o m p e t i t i v e l i g a n d l o s s by c o l l i s i o n - i n d u c e d d i s s o c i a t i o n has shown p r o m i s e b o t h f o r q u a l i t a t i v e and q u a n t i t a t i v e bond i n f o r m a t i o n [ 1 2 ] . D e s p i t e t h e s u c c e s s e s o f t h e above m e n t i o n e d t e c h n i q u e s f o r s t r u c t u r e and bond e n e r g y a n a l y s e s , i n h e r e n t u n c e r t a i n t i e s and l i m i t a t i o n s i n e a c h method make i t i m p o r t a n t t o d e v e l o p new and i n d e p e n d e n t t e s t s f o r comparison. I n t h i s r e g a r d our l a b o r a t o r y has i n i t i a t e d an i n t e n s i v e e f f o r t t o s t u d y t h e g a s - p h a s e p h o t o d i s s o c i a t i o n of t r a n s i t i o n metal c o n t a i n i n g i o n s [13-16]. A l t h o u g h a good d e a l o f i n f o r m a t i o n i s a v a i l a b l e on t h e p h o t o d i s s o c i a t i o n of o r g a n i c i o n s [ 1 7 l 8 ] , r e l a t i v e l y l i t t l e work has been done on o r g a n o m e t a l l i c i o n s [19>20]. FTMS i s i d e a l l y s u i t e d f o r t h e s e s t u d i e s b e c a u s e o f t h e wide v a r i e t y o f i n t e r e s t i n g i o n s t h a t can be g e n e r a t e d and b e c a u s e o f t h e l o n g s t o r a g e t i m e s w h i c h p e r m i t i r r a d i a t i o n o f the i o n s . I n t h i s p a p e r some o f t h e h i g h l i g h t s o f our work i s p r e s e n t e d t o g e t h e r w i t h a d e s c r i p t i o n o f t h e m e t h o d o l o g y and t h e t y p e s o f i n f o r m a t i o n t h a t can be o b t a i n e d from t h e s e s t u d i e s . f

Experimental Section The t h e o r y and i n s t r u m e n t a t i o n o f F o u r i e r t r a n s f o r m mass s p e c t r o m e t r y (FTMS) have been d i s c u s s e d e x t e n s i v e l y i n t h i s book and e l s e w h e r e [21-23]· A l l e x p e r i m e n t s were p e r f o r m e d on a N i c o l e t p r o t o t y p e FTMS-1000 F o u r i e r t r a n s f o r m mass s p e c t r o m e t e r p r e v i o u s l y d e s c r i b e d i n d e t a i l [24] and e q u i p p e d w i t h a 5.2 cm c u b i c t r a p p i n g c e l l s i t u a t e d between t h e p o l e s o f a V a r i a n 15 i n . e l e c t r o m a g n e t m a i n t a i n e d a t 0.85 T. The c e l l was c o n s t r u c t e d i n our l a b o r a t o r y and u t i l i z e s two 80$ t r a n s m i t t a n c e s t a i n l e s s s t e e l s c r e e n s as t h e t r a n s m i t t e r p l a t e s . This permits i r r a d i a t i o n w i t h a 2.5 kW Hg-Xe a r c lamp, used i n c o n j u n c t i o n w i t h a S c h o e f f e l 0.25 m monochromator s e t f o r 10 nm r e s o l u t i o n . M e t a l i o n s a r e g e n e r a t e d by f o c u s i n g t h e beam o f a Q u a n t a Ray Nd:YAG l a s e r ( e i t h e r t h e f u n d a m e n t a l l i n e a t 1064 nm o r t h e f r e q u e n c y d o u b l e d l i n e a t 532 nm) i n t o t h e c e n t e r - d r i l l e d h o l e (1 mm) of a h i g h p u r i t y r o d o f t h e a p p r o p r i a t e m e t a l s u p p o r t e d on t h e t r a n s m i t t e r s c r e e n n e a r e s t to the l a s e r . The l a s e r i o n i z a t i o n t e c h n i q u e f o r g e n e r a t i n g m e t a l i o n s has been o u t l i n e d elsewhere [25]. D e t a i l s of the c o l l i s i o n - i n d u c e d d i s s o c i a t i o n (CID) e x p e r i m e n t s have been d e s c r i b e d [ 2 6 ] . A r g o n was used as t h e c o l l i s i o n gas a t a t o t a l p r e s s u r e o f ~4 χ 10" torr. The c o l l i s i o n e n e r g y o f t h e i o n s can be v a r i e d ( t y p i c a l l y between 0 and 100 e V ) . A B a y a r d - A l p e r t i o n i z a t i o n gauge was used t o m o n i t o r s t a t i c p r e s s u r e s . Each o f t h e c h e m i c a l s was o b t a i n e d c o m m e r c i a l l y and used w i t h o u t f u r t h e r p u r i f i c a t i o n , e x c e p t f o r m u l t i p l e



158


freeze-pump-thaw c y c l e s t o remove n o n - c o n d e n s i b l e g a s e s . E l e c t r o n impact mass s p e c t r o m e t r y i n d i c a t e d no d e t e c t able i m p u r i t i e s . A l l samples were a d m i t t e d t o t h e c e l l t h r o u g h a G e n e r a l V a l v e Corp. S e r i e s 9 p u l s e d s o l e n o i d v a l v e [ 2 7 ] . The p u l s e d v a l v e , w h i c h was t r i g g e r e d con c u r r e n t l y w i t h t h e l a s e r p u l s e used t o g e n e r a t e t h e m e t a l i o n s , i n t r o d u c e d t h e r e a g e n t gas i n t o t h e vacuum chamber t o a maximum p r e s s u r e o f a p p r o x i m a t e l y 10 torr. A l t h o u g h t h e p u l s e d u r a t i o n o f t h e v a l v e was 2 ms, t h e h i g h p r e s s u r e o f t h e r e a g e n t gas had a r i s e time o f about 200 ms and was pumped away by a h i g h speed 5 i n . d i f f u s i o n pump i n a p p r o x i m a t e l y 400 ms. Swept d o u b l e r e s o n a n c e p u l s e s were t h e n used t o i s o l a t e t h e i o n o f i n t e r e s t , w h i c h was s u b s e q u e n t l y t r a p p e d f o r 3 - 6 s e c o n d s ( d e t e r m i n e d by t h e i o n ' s c r o s s s e c t i o n f o r p h o t o d i s s o c i a t i o n ) e i t h e r i n the presence or absence of r a d i a t i o n . For each i o n , two s e t s o f p h o t o d i s s o c i a t i o n s p e c t r a were t a k e n , one a t 2 χ 10 t o r r argon, t o permit c o l l i s i o n a l c o o l i n g , and a n o t h e r a t a b a c k g r o u n d p r e s s u r e o f "10" t o r r [ 2 8 ] . I n a l l c a s e s , d a t a from t h e c o l l i s i o n a l l y cooled ions are presented. P h o t o d i s s o c i a t i o n s p e c t r a were o b t a i n e d by m o n i t o r i n g t h e a p p e a r a n c e o f i o n i c p h o t o p r o d u c t s as a f u n c t i o n o f t h e wavelength of l i g h t . Shot-to-shot v a r i a t i o n of the l a s e r generated m e t a l p r e c u r s o r i o n s made m o n i t o r i n g t h e p h o t o disappearance of the parent i o n i m p r a c t i c a l . Assuming a o n e - p h o t o n p r o c e s s [ 1 7 , 2 9 ] , t h e p h o t o d i s s o c i a t i o n o f AB , eq. 1, can be d e s c r i b e d by f i r s t - o r d e r k i n e t i c s , eq. 2, where and are the a b s o l u t e c r o s s s e c t i o n s f o r f i

hv

+

d(AB )/dt

(1)

= -(σ

+

1

+ σ )Ι(ΑΒ )

(2)

2

r e

p r o d u c t i o n o f t h e p h o t o p r o d u c t s Ρ * and P?*' ~ s p e c t i v e l y , and I i s t h e p h o t o n f l u x . I n t e g r a t i n g eq. and s u b s t i t u t i n g (AB ) = (AB ) + (P ) ^ + +

+

h

p

1

+

( o )

t h e e x t e n t of p h o t o d i s s o c i a t i o n t o t h e 1. rrceilaait>eoss une c A ο c H υ u ι yu w u vu JL Ο Ο ν κ> λ. « . w λ. ν ** w ~ c r e s s s e cBtt i o n a t a g i v e n w a v e l e n g t h , eq. 3» where σ.

σ- + 1

-

i ss t h e t o t a l c r o s s s e c t i o n i + +• ln|1 + l * 2 oI t

σ d

0

['

P

and t i s t h e (3)

P

t

AB

+

J

i r r a d i a t i o n time. S o l v i n g eq. 3 f o r a and p l o t t i n g t h a t v a l u e as a f u n c t i o n o f w a v e l e n g t h , a p p r o p r i a t e l y c o r r e c t i n g f o r b l a n k s (no l i g h t ) , y i e l d s t h e p h o t o d i s s o c i a t i o n spectrum of the i o n ( i . e . , r e l a t i v e a vs. wavelength). C l e a r l y , the c o r r e c t spectrum r e q u i r e s t h a t a l l of the p h o t o d i s s o c i a t i o n p r o d u c t s be d e t e c t e d . Photoappearance c u r v e s f o r t h e i n d i v i d u a l p h o t o p r o d u c t s can be o b t a i n e d , f c

fc


10.

HETTICH AND FREISER



f o r example, by s o l v i n g eq. 4 f o r σ and p l o t t i n g a f u n c t i o n o f wavelength. Each s p e c t r u m r e p o r t e d

159

i t as i s an

average o f s e v e r a l t r i a l s . The r e p r o d u c i b i l i t y o f t h e peak i n t e n s i t i e s i s ± k0% and peak l o c a t i o n s i s ± 10 nm. P h o t o d i s s o c i a t i o n t h r e s h o l d s were c o n f i r m e d by u s i n g c u t off f i l t e r s . To o b t a i n a b s o l u t e v a l u e s f o r t h e c r o s s s e c t i o n s o f t h e i o n s b e i n g examined, t h e p h o t o d i s s o c i a t i o n o f C H g ( f r o m t o l u e n e a t 20 eV) a t 410 nm [σ(410 nm) = 0.05 A ] [ 3 0 ] was compared t o t h e p h o t o d i s s o c i a t i o n of a given i o n a t i t s b o t h t a k e n under s i m i l a r experimental conditions. A l l cross s e c t i o n s determined i n t h i s manner have an e s t i m a t e d u n c e r t a i n t y o f ± 50% due t o i n s t r u m e n t a l v a r i a b l e s . +

λ

Μ

χ

ί

R e s u l t s and D i s c u s s i o n on

C h e m i c a l Systems As l i s t e d below, o u r i n i t i a l s t u d i e s have f o c u s s e d three general c a t e g o r i e s o f metal c o n t a i n i n g i o n s : I.

II. III.

MFe

+

(M = 3d S e r i e s )

P h o t o d i s s o c i a t i o n o f simple metal i o n - l i g a n d s p e c i e s ( I ) can p r o v i d e i n f o r m a t i o n on t h e i r a b s o r p t i o n c h a r a c t e r i s t i c s (e.g., i s the a b s o r p t i o n o f l i g h t metal or l i g a n d l o c a l i z e d or o f a charge t r a n s f e r n a t u r e ? ) , s t r u c t u r e ( p a r t i c u l a r l y i n t h e c a s e o f i s o m e r s ) , and bond e n e r g y , as d i s c u s s e d i n g r e a t e r d e p t h below. The a d d i t i o n o f a s e c o n d l i g a n d ( I I ) a l l o w s one t o s t u d y t h e e f f e c t o f t h a t l i g a n d on t h e bond e n e r g y o f t h e f i r s t ( i . e . , a r e t h e r e any s y n e r g i s t i c a f f e c t s ? ) , as w e l l as i t s e f f e c t on t h e shape and c r o s s s e c t i o n o f t h e p h o t o d i s s o c i a t i o n s p e c t r a . As shown i n Scheme I , o x i d a t i v e a d d i t i o n o f a m e t a l i o n r e s u l t s i n f o r m a t i o n o f two new bonds t o t h e m e t a l c e n t e r . In f o r m u l a t i n g a s i m p l e e n e r g y d i a g r a m f o r such a p r o c e s s , i t i s g e n e r a l l y assumed t h a t t h e t o t a l l i g a n d b o n d i n g e n e r g y i s t h e sum o f t h e two i n d i v i d u a l m e t a l i o n - l i g a n d bond e n e r g i e s . W h i l e some i n f o r m a t i o n i s a v a i l a b l e on m u l t i p l e l i g a n d s y s t e m s [ 1 0 ] , i t i s q u i t e r a r e , and p h o t o d i s s o c i a t i o n holds promise f o r g r e a t l y expanding t h e d a t a base on t h i s q u e s t i o n . F i n a l l y , t h e a r e a o f c l u s t e r s i s a r a p i d l y g r o w i n g one. Our e f f o r t i n t h i s a r e a has been t o d e v e l o p a method f o r s y n t h e s i z i n g JLû s i t u a wide v a r i e t y o f d i m e r ( I I I ) [31-33] and t r i m e r i o n s [ 3 4 ] o f known c o m p o s i t i o n and s t u d y t h e i r g a s - p h a s e c h e m i s t r y .


160


Once a g a i n , p h o t o d i s s o c i a t i o n s t u d i e s can p r o v i d e complementary i n f o r m a t i o n on t h e s e c h e m i c a l l y important species.


Specific

ion

Synthesis

The u n i q u e f e a t u r e o f FTMS t o c o n t r o l b o t h t h e i o n and n e u t r a l p o p u l a t i o n s by u s i n g programmable p u l s e s e q u e n c e s makes i t an e x t r e m e l y p o w e r f u l t o o l f o r g e n e r a t ing i n a stepwise f a s h i o n s p e c i f i c o r g a n o m e t a l l i c fragment i o n s f o r s u b s e q u e n t c h e m i c a l and p h o t o c h e m i c a l studies. F i g u r e 1 shows a t y p i c a l p u l s e s e q u e n c e w h i c h b e g i n s w i t h an i o n i z a t i o n p u l s e . C o n c u r r e n t l y w i t h the l a s e r p u l s e , a p u l s e d v a l v e f i r e s t o admit a b u r s t of r e a g e n t gas. The m e t a l i o n s r e a c t w i t h t h e r e a g e n t gas t o f o r m t h e i o n o f i n t e r e s t , e i t h e r d i r e c t l y i n a primary or secondary r e a c t i o n , o r by a s u b s e q u e n t s t e p s u c h as c o l l i s i o n - i n d u c e d dissociation. F o r example, CoOH can be made by a d i r e c t primary r e a c t i o n of Co w i t h CH 0N0 ( r e a c t i o n 5) [ 1 3 ] , w h i l e m e t a l d i m e r s o f t h e f o r m M F e can be s y n t h e s i z e d +

+

+

Co

+

+

CH 0N0

>

3

CoOH

+

+

CH N0 2

(5)

i n a s t e p w i s e f a s h i o n from Fe(CO) by f i r s t g e n e r a t i n g MFe(CO) f o l l o w e d by c o l l i s i o n - i n d u c e d d i s s o c i a t i o n t o g e n e r a t e t h e b a r e M F e , r e a c t i o n s 6 and 7 [ 3 1 - 3 3 ] . Next, a s e r i e s o f i o n e j e c t i o n p u l s e s a r e used t o i s o l a t e t h e +

M

+

+

MFe(C0)

Fe(C0) + c

>

5

C

v

I

D

+

MFe(C0) _ +

> MFe

5

+

+

x

XCO

(5 -X)C0

(6) (7)

ion of i n t e r e s t . By t h i s t i m e t h e r e a g e n t gas has been pumped away, p e r m i t t i n g t h e i o n s t o be s t o r e d e f f i c i e n t l y f o r t h e r e l a t i v e l y l o n g t r a p p i n g t i m e s used f o r p h o t o dissociation. F o l l o w i n g an a p p r o p i a t e d e l a y p e r i o d ( w i t h o r w i t h o u t l i g h t ) , d e t e c t i o n y i e l d s t h e f u l l mass s p e c t r u m , and f i n a l l y a quench p u l s e e l i m i n a t e s a l l o f t h e i o n s from t h e c e l l and t h e whole s e q u e n c e i s r e p e a t e d .

Information

from

Photodisgocjatjon

I n o r d e r t o o b s e r v e p h o t o d i s s o c i a t i o n p r o c e s s 1, t h r e e c r i t e r i a must be met: f i r s t , t h e i o n must a b s o r b a p h o t o n ; s e c o n d , t h e p h o t o n must have s u f f i c i e n t e n e r g y t o c a u s e f r a g m e n t a t i o n ; and t h i r d , t h e quantum y i e l d f o r p h o t o d i s s o c i a t i o n must be n o n - z e r o . Figure 2 i s useful in u n d e r s t a n d i n g the i n f o r m a t i o n i n h e r e n t i n a photod i s s o c i a t i o n experiment. I f the f i r s t allowed e l e c t r o n i c s t a t e o f AB l i e s a t an e n e r g y above t h a t r e q u i r e d t o generate the p r o d u c t s P * and P * ( l e f t s i d e of F i g u r e 2 ) , the observed p h o t o d i s s o c i a t i o n onset i s s p e c t r o s c o p i c a l l y d e t e r m i n e d and y i e l d s o n l y an upper e n e r g y l i m i t f o r t h e p r o c e s s e s i n r e a c t i o n 1. In o t h e r words, even i f t h e r e i s s u f f i c i e n t e n e r g y i n t h e p h o t o n to c a u s e i o n f r a g m e n t a t i o n , c l e a r l y t h e p r o c e s s w i l l not o c c u r i f t h e i o n does not a b s o r b t h e p h o t o n . Alter+


10.

HETTICH AND FREISER


161

\Reagent Gas Pulse


/Ionization Synthesis

CID Excitation

Ion Ejection Separations

Detection

Quench

Product jAnalysis Structure J ' Determination,

• Reaction Time

F i g u r e 1.

P u l s e sequence used to s y n t h e s i z e , i s o l a t e , and s p e c i f i c metal-containing ions.

AB

+

•

— P.\ P

?

+

- AB

F i g u r e 2.

study

+

Energy l e v e l diagram d e p i c t i n g cases where photod i s s o c i a t i o n t h r e s h o l d s a r e d e t e r m i n e d by s p e c t r o s c o p i c f a c t o r s ( l e f t s i d e ) and thermodynamic f a c t o r s (right side).



162


n a t i v e l y , i f an a l l o w e d e l e c t r o n i c s t a t e f o r t u i t o u s l y l i e s a t t h e same e n e r g y as t h e l o w e s t e n e r g y p r o c e s s o r , as shown i n F i g u r e 2 ( r i g h t s i d e ) , t h e r e i s a h i g h d e n s i t y o f allowed s t a t e s having energies i n the v i c i n i t y of the thermodynamic t h r e s h o l d , t h e o b s e r v e d p h o t o d i s s o c i a t i o n o n s e t s h o u l d a c c u r a t e l y r e f l e c t t h e d i s s o c i a t i o n energy f o r p r o c e s s 1 p r o v i d e d t h e quantum y i e l d i s n o n - z e r o . Ons e t s f o r h i g h e r energy p r o d u c t s w i l l a l s o r e f l e c t t h e thermochemistry i f rapid i n t e r n a l conversion to a v i b r a t i o n a l l y e x c i t e d ground s t a t e o c c u r s r a n d o m i z i n g t h e energy. Thus, i f an i o n a b s o r b s l i g h t o v e r a broad r a n g e , say from t h e i r t o t h e uv, t h e n p h o t o d i s s o c i a t i o n c a n b e g i n t o o c c u r when t h e p h o t o n e n e r g y i s s u f f i c i e n t t o cause f r a g m e n t a t i o n . I n any e v e n t , t h e p h o t o d i s s o c i a t i o n s p e c t r u m i s an i n d i r e c t measure o f t h e t r u e g a s - p h a s e a b s o r p t i o n s p e c t r u m and, as such, p r o v i d e s a " f i n g e r p r i n t " of the ground s t a t e s t r u c t u r e o f t h e i o n . In g e n e r a l , t h e s t a t e d i a g r a m on t h e l e f t i n F i g u r e 2 i s a good d e s c r i p t i o n f o r o r g a n i c i o n s . As an example, t h e p h o t o d i s s o c i a t i o n s p e c t r u m o f b e n z o y l c a t i o n o b t a i n e d by m o n i t o r i n g p r o c e s s 8 has two maxima a t 260 nm and 310 nm C H CO 6

5

+

+ hv

C

H

> 6 5

+

+

0

0

(

8

)

1 1 1 a t t r i b u t e d to the t r a n s i t i o n s A^ 1u 1 2 . r e s p e c t i v e l y , and an o n s e t for p h o t o d i s s o c f a t i o n a t 350 nm o r 3.5 eV [ 1 8 ] . The o n s e t i s c o n s i d e r a b l y h i g h e r t h a n t h e a c t u a l e n t h a l p y o f 2.3 eV r e q u i r e d t o decarbonylate the benzoyl i o n . In c o n t r a s t t o t h e o r g a n i c i o n s , a l l o f o u r work t o d a t e on t h e c h e m i c a l s y s t e m s I, I I , and I I I , s u g g e s t t h a t t h e s e m e t a l c o m p l e x e s have a h i g h d e n s i t y o f low l y i n g e l e c t r o n i c s t a t e s and, t h e r e f o r e , a b s o r b b r o a d l y y i e l d i n g p h o t o d i s s o c i a t i o n o n s e t s w h i c h r e f l e c t t h e thermochemistry. I n p a r t i c u l a r , v a l u e s o b t a i n e d by o b s e r v i n g p h o t o d i s s o c i a t i o n o n s e t s a r e f o u n d i n g e n e r a l t o be i n good agreement w i t h t h o s e o b t a i n e d by o t h e r t e c h n i q u e s [15]. C e r t a i n l y , e x c e p t i o n s t o t h i s w i l l be f o u n d . F i n a l l y , a l t h o u g h the i n f o r m a t i o n c o n t e n t o f these photod i s s o c i a t i o n spectra i s great with regard to i o n s t r u c t u r e and t h e r m o c h e m i s t r y , t h e h i g h d e n s i t y o f low l y i n g e l e c t r o n i c s t a t e s makes band a s s i g n m e n t s v i r t u a l l y i m p o s s i b l e a t t h i s t i m e . I n f a c t such an i n t e r p r e t a t i o n w i l l p r o v i d e a r e a l c h a l l e n g e t o t h e o r i s t s f o r y e a r s t o come. B

a

n

d

A

B

(I)

P h o t o d i s s o c i a t i o n o f ML* One o f t h e f i r s t examples from o u r l a b o r a t o r y [13] which suggested t h a t p h o t o d i s s o c i a t i o n t h r e s h o l d s c o u l d y i e l d q u a n t i t a t i v e m e t a l - l i g a n d bond e n e r g i e s was from a c o m p a r i s o n o f t h e p h o t o d i s s o c i a t i o n s p e c t r a o f FeOH and F e C 0 o b t a i n e d by m o n i t o r i n g r e a c t i o n s 9 and 10, r e s p e c t i v e l y , and shown i n F i g u r e 3. The two s p e c t r a a r e r e m a r k a b l y s i m i l a r w i t h two a b s o r p t i o n maxima o b s e r v e d +


10.

HETTICH AND FREISER

163

Energy (eV)

(a)

5.0



4.0

3.0

2Ό

Wavelength (nm) (b)

Energy (eV)

5.0

4.0

3.0

20

Wavelength (nm)

Figure

3.

+

( a ) P h o t o d i s s o c i a t i o n spectrum o f FeOH o b t a i n e d by m o n i t o r i n g r e a c t i o n 9 as a f u n c t i o n o f wavelength. No p h o t o d i s s o c i a t i o n i s observed a t wavelengths greater than 390 nm. (b) P h o t o d i s s o c i a t i o n spectrum o f F e C 0 g e n e r a t e d by e l e c t r o n i m p a c t on Fe(CO) . The o b s e r v a t i o n o f p h o t o d i s s s o c i a t i o n a t w a v e l e n g t h s g r e a t e r t h a n 660 nm was c o n f i r m e d by u s i n g a c u t o f f f i l t e r . (Reproduced from r e f . 13. C o p y r i g h t 1984 American Chemical S o c i e t y . ) +


164


FeOH

+

+

hv

->

Fe

+

+

OH

(9)

FeCO

+

+

hv

>

Fe

+

+

CO

(10)

n e a r 290 nm and 335 nm, s u g g e s t i n g t h a t t h e t r a n s i t i o n s are metal l o c a l i z e d . The F e O H s p e c t r u m , however, has a p h o t o d i s s o c i a t i o n t h r e s h o l d o f 390 ± 1 0 nm, w h i l e F e C 0 i s o b s e r v e d t o have a low i n t e n s i t y l o n g w a v e l e n g t h a b s o r p t i o n t a i l from about 400 t o 700 nm. The c u t o f f o b s e r v e d a t 390 nm f o r F e O H y i e l d s an a b s o l u t e bond e n e r g y D ° ( F e - 0 H ) = 73±3 k c a l / m o l , w h i c h i s i n e x c e l l e n t agreement w i t h a v a l u e o f 76±5 k c a l / m o l o b t a i n e d by m e a s u r i n g t h e i o n i z a t i o n p o t e n t i a l o f FeOH [35] and a v a l u e o f 77±8 k c a l / m o l o b t a i n e d by b r a c k e t i n g t h e p r o t o n a f f i n i t y o f FeO [13]· A p p e a r a n c e p o t e n t i a l measurements on FeCO* from F e ( C 0 ) were i n t e r p r e t e d t o y i e l d D ( F e - C 0 ) s 60 k ? a l / m o l [ 3 6 ] . T h e s e same r e s u l t s , however, were l a t e r r e i n t e r p r e t e d t o y i e l d D ° ( F e - C 0 ) = 38 k c a l / m o l [ 3 7 ] . Observation of photodissociation re a c t i o n 10 a t "700 nm o r 41 k c a l / m o l p r o v i d e s a d d i t i o n a l support f o r the lower value. As shown i n T a b l e I , t h e e v i d e n c e i s m o u n t i n g t h a t p h o t o d i s s o c i a t i o n t h r e s h o l d s do i n f a c t y i e l d a c c u r a t e m e t a l - 1 i g a n d bond e n e r g i e s . I f there i s a disagreement between t h e p h o t o d i s s o c i a t i o n v a l u e and t h e v a l u e from an a l t e r n a t i v e technique, t h e p h o t o d i s s o c i a t i o n value tends to be l o w e r i n c o n t r a s t , f o r example, t o t h e b e n z o y l c a t i o n case d i s c u s s e d above. A r r i v i n g a t a l o w e r v a l u e by p h o t o d i s s o c i a t i o n suggests the p o s s i b i l i t y that the p r e c u r s o r i o n may be g e n e r a t e d w i t h e x c e s s i n t e r n a l energy [4b,38]. To c i r c u m v e n t t h i s p r o b l e m , once formed t h e p r e c u r s o r i o n s a r e p e r m i t t e d t o undergo t h e r m a l i z i n g c o l l i s i o n s w i t h a r g o n ( s e e e x p e r i m e n t a l s e c t i o n ) and t h e e f f e c t on t h e t h r e s h o l d , i f any, i s n o t e d . In addition, whenever p o s s i b l e , t h e p r e c u r s o r i o n o f i n t e r e s t was g e n e r a t e d from more t h a n one n e u t r a l s o u r c e . For the m a j o r i t y o f t h e s y s t e m s s t u d i e d , however, n e i t h e r t h e c o l l i s i o n a l c o o l i n g s t e p n o r t h e s y n t h e s i s from d i f f e r e n t n e u t r a l p r e c u r s o r s had a m e a s u r e a b l e e f f e c t on t h e threshold. One n o t a b l e a c c e p t i o n i s F e C H as d i s c u s s e d below. T r a n s i t i o n - m e t a l m e t h y l i d e n e s have been i m p l i c a t e d a s intermediates i n a v a r i e t y c f important c a t a l y t i c t r a n s f o r m a t i o n s i n c l u d i n g o l e f i n m e t a t h e s i s , t h e Ζiegler-Natta p o l y m e r i z a t i o n o f o l e f i n s , o l e f i n homologation, and t h e heterogeneous F i s c h e r - T r o p s c h process. Likewise, the i n c r e a s i n g l i t e r a t u r e on b a r e M C H * i n t h e g a s phase h a s shown t h e s e s p e c i e s t o have I n t e r e s t i n g p h y s i c a l and chemical p r o p e r t i e s [39-42]. I t i s perhaps not s u r p r i s ing, t h e r e f o r e , that the photochemistry of these s p e c i e s has p r o v e n t o be among t h e most i n t e r e s t i n g . Our i n i t i a l work on M C H * was f o r M = Fe and Co [14], b u t t h e s e s t u d i e s have r e c e n t l y been expanded t o i n c l u d e M = Rh, Nb, and L a [ 1 6 ] . The m e t h y l i d e n e s c a n be +

+


+

+

+

+

+

2


10.

HETTICH AND FREISER

Table

I.

Bond Energy


165

Determinations +

D°(A -B)(kcal/mol) photodissociation

A+-B +

Fe -CH Fe -CH Fe -C Co -CH Co -CIT Co -C Nb -CH Nb -CH Nb -C Rh -CH Rh -CIT Rh -C La -CH La -CH La -C Fe -CH Co -CH^ Fe -0 Fe -S Co -S Ni -S V -C H +

+

+

+


+

+

+

+

+

+

+

98 112

r

+

+

+

+

+

3

+

+

+

+

r

+

Co -C*H* SC -FI Ti -Fe V -Fe Cr -Fe Fe -Fe Co -Fe Ni -Fe Cu -Fe Nb -Fe Ta -Fe +

96±5 (b) 115±20 ( c ) 89 (c) 85±7 (d)

82±5( ' a) 101±5CoC H 2

+

8

a

(23)

H

5 10

+

The p h o t o d i s s o c i a t i o n s p e c t r u m o f C o - p e n t e n e . 320 nm. F i g u r e 5, i n d i c a t e s peak maxima a t 320 nm (σ = 0.02 A ) and 370 nm. A l l f i v e photoproducts are observed at w a v e l e n g t h s out t o a t l e a s t 430 nm. I f the photoappearance of Co i s due s o l e l y t o r e a c t i o n 23, t h e n o b s e r v a t i o n of Co a t 430 nm w o u l d i m p l y D°(Co -C H J < 66 k c a l / m o l . T h i s v a l u e must be e x p r e s s e d w i t h c a u t i o n , however, s i n c e t h e p r i m a r y p h o t o p r o d u c t s can a l s o f u r t h e r d i s s o c i a t e to give Co . +

+

1

+

II.

Photodissociation

of

ML^

The i o n o f s t r u c t u r e I I can be made p r e s u m a b l y by r e a c t i o n 24 [ 3 ] . The h i g h s t a t i c p r e s s u r e o f a r g o n

(24)

s t a b i l i z e s the c o n d e n s a t i o n of C o n t o CoC-Hg . P h o t o d i s s o c i a t i o n o f CoC H * frOm r e a c t i o n 24 ( F i g u r e 6) y i e l d s o n l y tnrèe p h o t o p r o d u c t s , r e a c t i o n s 25-27, w h i c h a r e a l l o b s e r v e d a t l e a s t out t o 430 nm. The r e l a t i v e a b u n d a n c e s o f t h e s e p h o t o p r o d u c t s were t a k e n a t

61* C H 2

4

(25)

->C0C H < 3

hv

6

15*

C

H

3 6

(26)

—> COC H/ -> Co (27) 5 10> 24* .2 L . = 320 nm(a= 0.05 k ) · No CoC.Hg o r CoC H« are o U s e r v e d , s u p p o r t i n g t h e f a c t t h a t t h i s i o n e x i s t s as s t r u c t u r e I I . The s p e c t r a o f t h e s e two i s o m e r s I and I I a r e a r e s i m i l a r , but t h e 370 nm peak o b s e r v e d i n t h e s p e c t r u m o f C o - p e n t e n e i s a b s e n t i n t h e s p e c t r u m o f Co (propene) ( e t h y l e n e ) . The enhanced p h o t o d i s s o c i a t i o n 2

( C

H

Y

+

+


•

HETTICH AND FREISER

Photodissociation of Transition Metal Ions 169

Energy (Kcal/mol) 90

80

70


Effect of Pressure on FeCH£

Wavelength (nm) F i g u r e 4.

Long wavelength t h r e s h o l d r e g i o n f o r Fed^" d i s s o c i a t i n g to F e at various pressures.

1-

photo-

+

ENERGY (Kcol/mol) 110 ~i—ι

250

90 1

300

1

350

70 1

400

Γ

450

WAVELENGTH (nm) F i g u r e 5. P h o t o d i s s o c i a t i o n spectrum o f C0C5H-LQ r e a c t i o n 18.

g e n e r a t e d from


170


c r o s s s e c t i o n o b s e r v e d f o r s t r u c t u r e I I ( i e . 0.05 A*) i s t y p i c a l o f a t r e n d we have o b s e r v e d t h a t p h o t o d i s s o c i a t i o n c r o s s s e c t i o n tends to i n c r e a s e w i t h the a d d i t i o n of a second l i g a n d [15]. The d i f f e r e n c e i n c r o s s s e c t i o n s a l o n e , however, would not be s u f f i c i e n t t o d i s t i n g u i s h t h e two i s o m e r s , A photoappearance t h r e s h o l d f o r Co , r e a c t i o n 27, c o u l d not be o b t a i n e d due t o t h e s e c o n d a r y d i s s o c i a t i o n o f CoC H / and CoC^H.."" t o y i e l d Co . R e c e n t l y we r e p o r t e d t h a t N i ( C H . ) c o u l d a l s o be d i s t i n g u i s h e d from t h r e e o t h e r i s o m e r s f N i - b u t e n e , Ni i s o b u t e n e , n i c k e l a c y c l o p e n t a n e c a t i o n ) on t h e b a s i s o f i t s u n i q u e p h o t o d i s s o c i a t i o n s p e c t r u m and p h o t o p r o d u c t s [15]· In p a r t i c u l a r N i i C - H j . ) * p h o t o d i s s o c i a t e s t o g i v e two p r o d u c t s o f about e q u a l abundance (by l o s s o f C H^ and C.Hg). Continuous e j e c t i o n of Ni -C H . allows r e a c t i o n 28 t o be m o n i t o r e d . As shown i n F i g u r e 7 , +

1

+

+

2

J

2


+

+

2

+

2

||-

N i * -||

+

hv

> Ni

+

+

2

i

C H 2

(28)

4

,

r e a c t i o n 28 i s o b s e r v e d f o r < 370 nm i m p l y i n g D°(Ni* "-2 p i i ) = 77±5 k c a l / m o l . The f a c t t h a t t h i s v a l u e i s net s i g n i f i c a n t l y d i f f e r e n t t h a n t w i c e D ° ( N i - C H ) = 37±2 k c a l / m o l s u g g e s t s t h a t s y n e r g i s t i c e f f e c t s a r e not very pronounced i n t h i s i o n . W h i l e t h i s may p r o v e t o be t y p i c a l , i t i s not e x p e c t e d t o be t h e r u l e . F o r example, p r e l i m i n a r y s t u d i e s on t h e b i s - b e n z e n e i o n s , ( 5 6)o ' suggest a n e g l i g i b l e s y n e r g i s t i c e f f e c t f o r M = V [l5J and Sc [ 4 4 1 , a n e g a t i v e e f f e c t f o r L a ( i . e . , D°(La* -C.H ) > D ( L a C H . - C.H.), and a p o s i t i v e e f f e c t f o r Cu ? i . e. , B°t C u - C . H, ) < D°( CuC. H."* - C H ) [44]. c

H

+

2

M

4

C

H

+

+

+

fi

A

+

+

6

6

III.

6

6

6

6

P h o t o d i s s o c i a t i o n o f MFe+

E x a m i n a t i o n o f t h e b o n d i n g and e n e r g e t i c s o f s m a l l b a r e c l u s t e r s has become a t o p i c o f c o n s i d e r a b l e i n t e r e s t in recent years. An e x c i t i n g a r r a y o f methods has been d e v e l o p e d t o g e n e r a t e c l u s t e r s o f v a r y i n g s i z e s and c o m p o s i t i o n f o r s t u d y i n t h e gas phase. Some of t h e s e new methods i n c l u d e s p u t t e r i n g t e c h n i q u e s [ 4 5 ] , gas e v a p o r a t i o n techniques [46], supersonic expansion techniques w i t h oven [47] and p u l s e d l a s e r s o u r c e s [ 4 8 ] , and m u l t i p h o t o n d i s s o c i a t i o n o f m u l t l n u c l e a r o r g a n o m e t a l l i c compounds [ 4 9 ] . As d e s c r i b e d above, our l a b o r a t o r y dem o n s t r a t e d t h e s y n t h e s i s o f s m a l l h o m o n u c l e a r and h e t e r o n u c l e a r t r a n s i t i o n m e t a l c l u s t e r i o n s ±n _s_i£_u. by u s i n g FTMS [ 3 1 - 3 3 ] . F o r example, r e a c t i o n s 6 and 7 have been used t o s y n t h e s i z e a wide v a r i e t y o f M F e s p e c i e s . The c l e a r a d v a n t a g e s o f t h i s method a r e t h a t not o n l y i s there a great deal of s e l e c t i v i t y i n generating s p e c i f i c c l u s t e r s , but once formed t h e f u l l power o f FTMS can be a p p l i e d t o s t u d y the c h e m i s t r y and p h o t o c h e m i s t r y o f t h e s e species in d e t a i l . T h i s a p p r o a c h i s t y p i f i e d by ext e n s i v e s t u d i e s on t h e r e a c t i v i t i e s o f C o F e [ 3 2 ] and VFe [33] with alkenes. I n a soon t o be p u b l i s h e d +

+

+



10. HETTICH AND FREISER


ENERGY 110

100

171

( KCAL/MOL )

90

80

70

IK-II

6

hv.

Ni

0

+

Ο BLANK i

—-

—

e

Γ ι ι ι ι I 300

250

ι

ι

JL

ο · οι

350

ι

I

ι

ι

ι I ι

J

150

100

WAVELENGTH ( NM ) Figure

7.

T h r e s h o l d r e g i o n f o r N i ( C H J photod i s s o c i a t i n g t o N i . I n t h sie x p e r i m e n t , was c o n t i n u o u s l y e j e c t e d . Ν10 Η 2

+

-

Ί

2

4


L

172


paper [ 1 6 ] , we expand on t h i s work by r e p o r t i n g on t h e p h o t o d i s s o c i a t i o n o f MFe (M = Se, T i , V, C r , Fe, Co, N i , Cu^ Nb, T a ) . To summarize t h o s e r e s u l t s , b o t h M and Fe a r e o b s e r v e d as p h o t o p r o d u c t s , w i t h t h e m e t a l h a v i n g t h e l o w e s t i o n i z a t i o n p o t e n t i a l p r e d o m i n a t i n g . The p h o t o d i s s o c i a t i o n s p e c t r a r e v e a l broad a b s o r p t i o n i n t h e u l t r a v i o l e t and v i s i b l e r e g i o n s w i t h a range o f c r o s s s e c t i o n s from 0.06 A f o r VFe t o 0.62 A f o r f o r CrFe . Bond e n e r g i e s o b t a i n e d by o b s e r v i n g p h o t o a p p e a r a n c e ons e t s a r e i n t h e range o f 48 k c a l / m o l f o r S c F e t o 75 kcal/mol f o r VFe ( s e e T a b l e I ) . T h e s e s t u d i e s c a n be r e a d i l y e x t e n d e d t o o t h e r d i m e r s e r i e s , s u c h as MV , M C r , and MCo g e n e r a t e d i n a n a l o g y t o r e a c t i o n s 6 and 7 from V ( C 0 ) , C r ( C 0 ) , and C o ( C 0 ) N 0 , r e s p e c t i v e l y , as w e l l as t o t r i m e r s [ 3 4 ] and n i g h e r o r d e r clusters. C l e a r l y , t h e s u r f a c e has j u s t been s c r a t c h e d ! +

+

+

+


+

+

+

+

6

6

3

Acknowledgment i s made t o t h e D i v i s i o n o f C h e m i c a l S c i e n c e s i n t h e O f f i c e o f B a s i c Energy S c i e n c e s i n t h e u n i t e d S t a t e s Department o f Energy (DE-AC02-80ER10689) f o r s u p p o r t i n g t h i s r e s e a r c h and t o t h e N a t i o n a l S c i e n c e F o u n d a t i o n ( C H E - 8 3 1 0 0 3 9 ) f o r c o n t i n u e d s u p p o r t o f FTMS methodology. The a u t h o r s a l s o w i s h t o thank M i c h e l l e Buchanan f o r h e r i n v i t a t i o n t o c o n t r i b u t e t o t h i s symposium.

References 1.

2. 3. 4.

5. 6. 7. 8. 9. 10. 11.

For a comprehensive review on gas-phase metal ion chemistry see: Allison, J . in Progress in Inorganic Chemistry, Ed. Lippard, S. J., Wiley - Interscience, New York, Vol. 34, 628, 1986. Halle, L.F.; Houriet, R.; Kappes, M.; Staley, R.H.; Beauchamp, J . L . J . Am. Chem. Soc. 1982, 104, 6293. Jacobson, D.B.; Freiser, B.S.; J. Am. Chem. Soc. 1983, 105, 5197. (a) Larsen, B.S.; Ridge, D.P. J . Am. Chem. Soc. 1984, 106, 1912. (b) Freas, R.B.; Ridge, D.P. J . Am. Chem, Soc., 1980, 102, 7129. (c) Armentrout, P.B.; Beauchamp, J.L.; J. Am. Chem. Soc., 1980, 102, 1736. Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1985, 107, 72. Houriet, R.; Halle, L.F.; Beauchamp, J . L . Organonetallics 1983, 2, 1818. Allison, J.; Freas, R.B.; Ridge, D.P., J. Am. Chem. Soc., 1979, 101, 1332. Armentrout, P.B.; Beauchamp, J . L . J . Am. Chem. Soc. 1981, 103, 784. Aristov, N.; Armentrout, P.B. J . Am. Chem. Soc 1984, 106, 4065. Jones, R.W.; Staley, R.H. J. Am. Chem. Soc. 1982, 104, 2296. Uppal, J . S . ; Staley, R.H. J . Am. Chem. Soc. 1982, 104, 1235.


10. HETTICH AND FREISER

12. 13. 14. 15.


16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

26. 27. 28.

29. 30. 31. 32. 33. 34. 35. 36. 37.

Photodissociation of Transition Metal Ions 173

McLuckey, S.A., Schoen, A.E.; Cooks, R.G. J. Am. Chem. Soc. 1982, 104, 848. Cassady, C . J . ; Freiser, B.S. J . Am. Chem. Soc. 1984, 106, 6176. Hettich, R . L . ; Freiser, B.S. J . Am. Chem. Soc. 1986, 108, 2537. Hettich, R . L . ; Jackson, T . C . ; Stanko, E . M . ; Freiser, B.S. J . Am. Chem. Soc. 1986, 108, 5086. Hettich, R . L . ; Freiser, B.S. J. Am. Chem. Soc., in press. Dunbar, R.C. "Gas Phase Ion Chemistry;" Bowers, M.T., E d . ; Academic Press, Inc.; New York, 1984; Vol. 3, Chap. 20. Freiser, B.S.; Beauchamp, J . L. J . Am. Chem. Soc. 1976, 98, 3136. Dunbar, R.C.; Hutchinson, B.B. J . Am. Chem. Soc. 1974, 96, 3816. Burnier, R.C.; Freiser, B.S. Inorg. Chem. 1979, 18, 906. Comisarow, M.B. Adv. Mass Spec. 1980, 8, 1698. Gross, M . L . ; Rempel, D.L. Science 1984, 226, 261. Lande, Jr.,D.A.; Johlman, C . L . ; Brown, R.S.; Weil, D.A.; Wilkins, C.L. Mass Spec. Rev. 1986, 5, 107. Cody, R.B.; Burnier, R.C.; Freiser, B.S. Anal. Chem. 1982, 54, 96. Cody, R.B.; Burnier, R.C.; Reents, Jr., W.D.; Carlin, T.J.; McCrery, D.A.; Lengal, R.K.; Freiser, B.S. Int. J . Mass Spec. Ion Phys. 1980, 33, 37. Cody, R.B.; Burnier, R.C.; Freiser, B.S. Anal. Chem. 1982, 54, 96. Carlin, T.J.; Freiser, B.S. Anal. Chem. 1983, 55, 571. The photodissociation spectra of a l l of the ions showed no pressure dependence, except for slight quenching of the low energy t a i l region, indicating that photodissociation in these cases is probably due to one-photon excitation and that the precursor ions do not have substantial internal energy. Freiser, B . S . ; Beauchamp, J . L . Chem. Phys. Lett. 1975, 35, 35. Dunbar, R.C. Chem. Phys. Lett. 1975, 32, 508. Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1984, 106, 4623. Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1985, 107, 1581. Hettich, R . L . ; Freiser, B.S. J . Am. Chem. Soc. 1985, 107, 6222. Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1984, 106, 5351. Murad, E. J . Chem. Phys. 1980, 73, 1381. Distefano, G.J. Res. Natl. Bur. Stand, Sect. A. 1970, 74A, 233. Halle, L.F.; Armentrout, P.B.; Beauchamp, J . L . Organometallics 1982, 1, 963. Buchanan; Fourier Transform Mass Spectrometry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

174

38.

39.


40. 41. 42. 43.

44. 45.

46.

47.

48.

49.


Metal ions can be made with excess internal and/or kinetic energy. See, for example, (a) Kang, H . ; Beauchamp, J . L . J . Phys. Chem. 1985, 89, 3364. (b) Halle, L.F.; Armentrout, P.B.; Beauchamp, J . L . J . Am Chem. Soc., 103, 962 (1981). (a) Stevens, A . E . ; Beauchamp, J . L . J . Am. Chem. Soc. 1980, 100, 2584. (b) Stevens, A . E . ; Beauchamp, J . L . J . Am. Chem. Soc. 1979, 101, 6449. Armentrout, P.B.; Halle, L.F.; Beauchamp. J . L . J . Am. Chem. Soc. 1981, 103, 6501. (a) Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1985, 107, 2605. (b) Jacobson, D.B.; Freiser, B.S. J . Am. Chem. Soc. 1985, 107, 4375. (a) Carter, A . E . ; Goddard III, W.A. J . Am. Chem. Soc. 1986, 108, 2180. (b) Shim, I . ; Gingerich, K.A. J . Chem. Phys. 1982, 76, 3833. A l l heats of formation (and other supplementary values) are taaken from: Rosenstock, H.M.; Draxl, K.; Steiner, B.W.; Herron, J . T . J . Phys. Chem. Ref. Data. Suppl. 1 1977, 6. Lech, L . M . ; Tews, E . C . ; Huang, Y . ; Freiser, B.S. unpublished results. (a) Katakuse, I . ; Ichihara, T . ; F u j j i t a , Y . ; Matsuo, T . ; Sakurai, T . ; Matsuda, H. Int. J . Mas Spec. Ion Proc. 1985, 67, 229. (b) Freas, R.B.; Campana, J . E . J . Am. Chem. Soc. 1985, 107, 6202. (a) Sattler, K . ; Muhlbach, J.; Recknagel, E. Phys. Rev. Lett. 1980, 45, 821. (b) Abe, H.; Schulze, W.; Tesche, B. Chem. Phys. 1980, 47, 95. (c) Godenfeld, I . ; Frank, F . ; Schulze, W.; Winter, B. Int. J . Mass Spec. Ion Proc. 1986, 71, 103. (a) Riley, S . J . ; Parks, E . K . ; Mao, C.R.; Poppo, L . G . ; Wexler, S. J . Phys. Chem. 1982, 86, 3911. (b) Bowles, R.S.; Park, S.B.; Otsuka, N.; Andres, R.P. J. Mol. Catal. 1983, 20, 279. (a) Bondybey, V . E . ; English, J . H . J . Chem. Phys. 1982, 74, 6978. (b) Morse, M.D.; Hansen, G.P.; Langridge-Smith, P.R.R.; Zheng, L . S . ; Geusic, M . E . ; Michalopoulos, D . L . ; Smalley, R.E. J . Chem. Phys. 1984, 80, 5400. (c) Smalley, R.E. Laser Chem. 1983, 2, 167. Leopold, D.G.; Vaida, V. J . Am. Chem. Soc. 1983, 105, 6809.

RECEIVED May 12,

1987


Gas-Phase Photodissociation of Transition Metal Ion Complexes and

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