Bulletin Autumn‧Winter 1999

up GeH 7 + , into GeH 5 + and H 2 . This means that GeH 7 + is n ot a v e r y stable species b u t one w h i c h shou l d exist l ong enough f o r e x p e r i m e n t a l d e t e c t i o n a n d characterization, as it has been f ound that SiH 7 + , w i t h a corresponding dissociation ene r gy of about 4.6 k c al mol -1 , can be observed spectroscopically. I n the second part of the project. Profs. L i a n d So t a r g e t e d n o v e l c h e m i c al compounds wh i ch were po l l u t i on causin g s u c h as o r g a n o s u l f u r c o m p o u n d s . E x p e r i m e n t s h a v e s h o w n t h a t t he o r g a n o s u l f ur c o m p o u n d CH 3 SSCH 3 breaks u p into CH 3 , whose structure is we l l k n o w n t o c h em i s t s , a n d t h e s u l f u r - c o n t a i n i ng f r a g m e n t, CH 3 S 2 w h o s e structure is u n k n o w n . CH 3 S 2 has ma ny possible structures, some of w h i c h are shown in Figure 2. Combining experimental data f r om I owa State Universit y and their o w n c omp u t a t i o n al results , the C U H K r esea r che rs d e d u c ed t h a t t he CH 3 S 2 f r a gme n t has the s t r u c t u re s h o wn i n Figure 2 (a). This knowledge is useful for understanding th e dissociation channels of the air pollutan t CH3SSCH3. I n a related experiment b y the I owa State researchers, l i g h t wa s shone on CH 3 SSCH 3 to simulat e wh a t happen s i n the atmosphere w h e n the su n shines o n pollutants i n the air. This caused a reaction k n o wn as 'dissociative pho t o i on i za t i on ' w h e r e i n CH 3 SSCH 3 b r o ke u p i n t o the fragments CH 3 and CH 3 S 2 + . (Note that the only difference betwee n CH 3 S 2 + and CH 3 S 2 , men t i oned earlier, is that the CH 3 S 2 + has one fewer electron. ) Once again, w h i l e experimentalists k n ew tha t CH 3 S 2 + wa s f o rmed , they d i d no t k n ow its structure. Valance theory, wh i ch explains relations be t ween atoms i n c ompound s, predicts many structures for CH 3 S 2 + , some of wh i c h are s h own i n Figure 3. By comb i n i ng the q u a n t i t a t i v e da ta i n t he d i s s o c i a t i ve p h o t o i o n i z a t i o n e x p e r i m e n t w i t h calculations, the researchers identified the structure of CH 3 S 2 + to be the one shown i n Figure 3 (c). C h i n e s e U n i v e r s i t yB u l l e t i n A u t u m n • W i n t e r 1999 36