experimental in the physics

7/30/2019 Experimental in the physics

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C H A P T E R 2ExperimentalI. So lid s (Excluding Single Crystals) 25

A. Mull Technique 26B. Potassium Brom ide (KBr) Disk Techniques 26C. Solutions (Solids, Liquids, and Gases) 27II. Liquid Films (See the Foreme ntioned I - C for Liquids in Solution)and Cast Polymer Films 27III. Vap ors and Gases 28References 30

S ample p repara t ion i s a ve ry imp or tan t pa r t o f the IR techn ique . Becaus e chemica l s can ex i s t inthe s o l id , l iqu id , vapor , o r s o lu t ion phas es , d i f f e r en t me th ods o f p repara t ion a r e r equ i r ed in o rde rto be ab le to r eco rd the i r IR s pec t r a . Th i s chap te r i s no t in tended to inc lude a l l me thods o fob ta in ing IR s pec t ra . I t inc ludes on ly the m etho ds us ed to acqu i re the da ta inc lude d in th i s book .

I. S O L I D S ( E X C L U D I N G S I N G L E C R Y S T A L S)S ol id s amples a r e us ua l ly p repared as mul l s o r a s KBr pe l l e t s . Bo th t echn iques r equ i r e tha t thepar t ic le s ize be smaller than 2 .5 ~ t . Larger par t ic les scat ter IR radiat ion via Rayleigh scat ter ing inthe IR r eg ion o f in ter es t . F o r exam ple , i f pa r t ic les a r e p res en t in dec reas ing c once n t r a t ion f rom2.5 through 25 ~ t , the basel ine of the spectrum wil l s lope upward in the region 2 .5 to 25 ~ t (4000-4 0 0 c m - 1 , t h e r e g io n m o s t c o m m o n l y e x a m i n e d b y c h e m i s t s ).

Thus , s o l id s amples mus t be g round us ing a mor ta r and pes t l e (o r a w igg le bug) to mee t thep reced ing r equ i r emen ts . The c los e r one ge t s to a v i r tua l ho r izon ta l bas e l ine , the be t t e r thequa l i ty o f the IR s pec t rum. The bands o f the chemica l s o l id s t a r t abs o rb ing IR r ad ia t ion a t thepo in t o f the bas e l ine where the i r v ib ra t iona l f r equenc ies occur in th i s r eg ion o f the s pec t rum.There i s ano th e r f ac to r tha t caus es d i s to r t ion o f IR abs o rp t ion bands . I f the r e f r act ive index o fs o l id pa r t i c les and the s u r round ing med ium d i f f e r apprec iab ly , the Chr i s t i ans en e f f ec t i senco un te red (1 ). The Chr i s t i ans en e f fec t deve lops becaus e the r e f r ac tive index o f a chemica li s a func t ion o f f r equency tha t has a d i s con t inu i ty in each f r equency r eg ion o f a s t rongabs orp t ion band . The r e f r ac t ive index f a l l s r ap id ly on the h igh f r equency s ide o f the abs o rp t ion

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2 6 Experimentalm a x im u m an d o n th e lo w f r eq u en cy s id e th e r e f rac t iv e in d ex f al ls r ap id ly f ro m a h ig h v a lu e to i t sv a lu e o f n o ab so r p t io n . T h i s e f fec t c au se s p ecu l i a r ab so r p t io n b a n d d i s to r t i o n w h en th e r e a r em an y l a r g e p a r t i c l e s p r e sen t d u e to i n ad eq u a te sam p le p r ep a r a t io n . T h e Ch r i s t i an sen e f f ec t i sm in im ized b y a r ed u c t io n o f a s m an y p a r t i cl e s a s p o ss ib l e sm a l l e r t h an 2 ~ in s iz e . Ho wev e r , t h ee f fec t is n ev e r co m p le t e ly e l im in a ted wh en r eco r d in g sp ec t r a o f p o w d e r ed c r y s t a ll i n e m a te r i a ls .

A . M U L L T E C H N I Q U EAf te r t h e sam p le h a s b een p r o p e r ly g r o u n d , N u j o l o i l o r F lu o r o lu b e i s ad d ed an d m ix ed in o r d e rto suspend the par t ic les in the mul l ing agen t . However , i t i s p referab le to g r ind the so l id in thep r e sen ce o f t h e m u l l in g ag en t t o h e lp in th e g r in d in g p r o cess . T h e m u l l in g ag en t s su s p en d th eso l id p a rt i c le s , wh ic h h e lp s t o p r o d u ce a c lo se r m a tch o f t h e r e f rac t iv e in d ex b e twee n th e sep a r t i c le s an d th e su r r o u n d in g m ed iu m . N u j o l i s u se f u l f or r e co r d in g I R sp ec t r a i n t h e r eg io n1 3 3 3 - 4 0 0 c m - 1 , an d F lu o r o lu b e i s u se f u l f o r r e co r d in g I R sp ec t r a i n t h e r eg io n 4 0 0 0 -1 3 3 3 cm - 1 . I n o r d e r t o pl ace th e se m u l l ed su sp en s io n s in t h e I R sam p le co m p ar tm en t ,so d iu m ch lo r id e an d / o r p o ta ss iu m b r o m id e p l a t e s a r e r eq u i r ed . A F lu o r o lu b e m u l l p a s t e i sth en p l aced b e tween two so d iu m ch lo r id e p l a t e s o r two p o ta ss iu m b r o m id e p l a t e s u s in g p r e ssu r eto o b ta in th e p r o p e r t h i ck n ess o f t h is p a s t e i n o r d e r t o o b ta in a q u a li t y IR sp ec t r u m in th e r eg io n4 0 0 0 - 1 3 3 3 cm - 1 th a t i s e s sen t i a ll y v o id o f s ig n i fi c an t F lu o r o lu b e ab so r p t io n b an d s . I n t h e r eg io n1 3 3 3 - 4 0 0 c m - 1 t h e p r o c e ss i s re p e a t e d u s i n g t h e N u j o l m u l l s u s p e n s i o n b e t w e e n p o t a s s i u mb r o m id e p l a t e s , wh ich m in im izes ab so r p t io n f r o m N u j o l o i l .

B . P O T A S S I U M B R O M I D E ( K B r ) D I S K T E C H N I Q U EAfter g r ind ing the so l id to p roper par t ic le s ize , KBr is mixed wi th the so l id par t ic les . A ra t ioso m ew h er e b e tw een 5 0 to 1 0 0 K B r : I o f so l id sam p le u su a l ly p r o d u ces a q u a l i t y IR sp ec t r u m .T h e KBr an d g r o u n d p a r t i c le s a r e t h en th o r o u g h ly m ix ed to p r o d u ce a u n i f o r m m ix tu r e . Fu r th e rg r in d in g o f t h e m ix tu r e sh o u ld b e av o id ed b ecau se th i s ad d i t i o n a l g r in d in g wi l l u su a l ly i n d u cewa te r i n to t h e m ix tu r e . T h e p r o p e r am o u n t o f t h i s KBr p r ep a r a t io n i s p l aced in a sp ec i a l di e , an da d i sk is p r e ssed u s in g ap p r o x im a te ly 9 6 0 0 Kg p r e ssu re . T h e d i sk i s p l aced in a h o ld e r an d p l acedth en in t h e sam p le co m p ar tm en t o f t h e IR sp ec t r o m e te r .

Bo th th e m u l l an d KBr p r e ssed d i sk t e ch n iq u e can cau se ch an g es to t h e sam p le . G r in d in go r i n c r ea sed p r e ssu r e u p o n th e sam p le can cau se ch an g es in c r y s t a l l in e f o r m o f t h e sam p le .I n ad d i t i o n , t h e p r e ssed KBr d i sk can cau se ch em ica l r e ac t io n s to o ccu r b e twe en KBr an dt he s a m p l e ( e .g ., R - N H + C I - + K B r ~ R - N H + B r - + K C 1 ) . I n t he m u l l t e c h n i q ue i o nex ch an g e can a l so o ccu r b e tween th e win d o w an d th e su sp en d ed sam p le ( e .g . ,R - - N H 3 + F - + K B r ~ R - N H 3 + B r - ) . T h is la tt er re a c ti o n o c c ur s w h e n p r e s s ur e be t w e e n t hep la t e s t o g e th e r w i th p l a t e r o t a t io n cau se s so l id s t a t e i n t e r ac t io n b e tween th e p l a t e s an d th esam p le . T h u s , o n e sh o u ld b e awar e th a t t h e ch em is t c an in ad v e r t en t ly a l t e r t h e o r ig in a l sam p led u r in g p r ep a r a t io n , t h e r eb y cau s in g p r o b lem s in t h e so lu t io n o f t h e ch em ica l p r o b lem a t h an d .

T h e I R sp ec t r a o f so l id s o b ta in ed a f t er ev ap o r a t in g wa te r so lu t io n s to d r y n ess can a l so b er eco r d ed u s in g th e m u l l o r KBr d i sk t e ch n iq u e .


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V a r i a b l e s i n D a t a I n t e r p r e t a t i o n 27C . S O L U T I O N S ( S O L I D S , L IQ U I D S , A N D G A S E S )Sol ids , l iqu ids , and gases a re of ten so luble in so lvents such as carbon te t rach lor ide and carbondisu l f ide . Other so lvents such as ch loroform, methylene ch lor ide , o r d imethyl su l fox ide (DMSO)can a l so be used depen ding upo n the par t icu lar p roblem . Since like d isso lves like , the more po larso lvents a re used to d isso lve the more po lar compounds. Carbon te t rach lor ide and carbondisu l f ide are used to d isso lve the less po lar compounds.

Carbon te t rach lor ide i s a usefu l so lvent in the reg ion 4000-1333 c m - 1 and carbon d isu l f ide i sa usefu l so lvent in the reg ion 13 33 -4 00 cm -1 . This i s because these so lvents have the leas tabsorp t ion in these reg ions . Qual i ty IR spec t ra can be recorded using samples prepared a t 10%by weight in each of these so lvents , and p lac ing the so lu t ions in 0 .1-mm sodium chlor ide ce l l( 4 0 0 0 - 1 3 3 3 c m - 1 fo r CC14 so lu ti o n s ) an d 0 .1 -m m p o t a ss i u m b ro m i d e ce l l (1 3 3 3 -4 0 0 cm -1 fo rCS2 so lu t ions) . Com parable IR spec t ra wi l l be recorded using 1% by weight us in g 1 .0-mm cell s;however , absorp t ion from the so lvent wi l l be increased by a fac tor o f 10 . Varia t ion ofco n cen t ra t i o n an d ce l l p a th l en g th can b e u sed t o reco rd t h e sp ec t ru m mo s t u se fu l in o b t a in i n gusefu l chemica l in format ion . For example , changing the concent ra t ion of a chemica l , in sayCC14, can he lp to d is t inguish be tw een in ter- and in t ramolec ular hyd roge n bonding . The O H orNH st re tch ing frequencies rem ain essen t ia l ly unc han ged upo n d i lu t ion , in the case of in t ra-mo lecu l a r h y d ro g en b o n d in g , b u t i n c rea se mark ed ly i n f req u en cy u p o n d i l u t i o n i n t h e ca se o fi n t e rmo lecu l a r h y d ro g en b o n d in g .

Solu t ion spec t ra a re very usefu l in performing quant i ta t ive analysis when both the sampleconce nt ra t ion and ce l l pa th length are know n, prov id ing the absorbance of a band due to thepresence of the cr i t ica l ana ly te can be d irec t ly measured . In the wo rs t case , in terference from thepresence of another ana ly te may have to be subt rac ted before the analysis can be performed onthe cri t ical analyte in quest ion.

A so lvent such as CSz i s a l so usefu l fo r ex t rac t ing som e chem icals f rom w ater . After thoro ughshaking wi th water , the sample can be concent ra ted by par t ia l so lvent evapora t ion in a wel l -vent i la ted hood conta in ing no source of ign i t ion . The sample i s then sa l ted us ing dry NaC1pow der in order to remove w ater . The CS2 i s then p laced in a su i tab le KBr ce l l before the so lu t ionspect rum is recorded . This same so lvent can be used to ex t rac t cer ta in addi t ives f rom polymercomposi t ions .

I I. L I Q U I D F I L M S (S EE T H E F O R E M E N T I O N E D I - C F O RL I Q U I D S I N S O L U T I O N ) A N D C A S T P O L Y M E R F I L M S

a. Liquid f i lms be tw een KBr p la tes a re eas i ly prepared b y p lac ing a drop or mo re on on e p la teand then p lac ing the second p la te on top wi th enough pressure to form the desi red f i lmth ickness . Very vo la t i le l iqu ids a re be t te r p repared as so lu t ions .b . IR spec t ra of po lym ers a re of ten record ed of f rees tanding f i lm or of f ilms cas t on a su i tab leIR p la te . Frees tanding f i lms are prepared by hea t ing po lymeric mater ia l above i t s mel t ing po in tbe tween hea ted p la tes in a su i tab le press . The f i lm i s a l lowed to cool to ambien t tempera turebefore removing i t f rom the meta l p la tes . The frees tanding f i lm i s then p laced in the IRspect rometer .


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28 Experimentalc . I R sp ec t r a a r e o f t en r eco r d ed o f p o ly m er i c su b s t an ces ca s t f r o m b o i l i n g so lu t io n o n to a

p r eh ea t ed KBr p l a t e , o f t en u n d e r a n i t r o g en a tm o sp h e r e in o r d e r t o av o id o x id a t io n o f t h ep o ly m er . Af t e r t h e so lv en t h a s ev ap o r a t ed , t h e p l a t e an d f i lm a r e a l l o wed to co o l t o am b ien tt em p e r a tu r e b e f o r e p l ac in g in t h e I R sam p le co m p ar tm en t . Fa i lu r e t o p r eh ea t t h e KBr p l a t e w i l lc au se i t t o sh a t t e r wh en f i r s t i n co n tac t w i th t h e h o t so lu t io n . Mo r eo v e r , r em o v a l o f t h e h ea t edcas t f i lm a f t e r so lv en t ev ap o r a t io n to a am b ien t en v i r o n m en t w i th o u t p r io r co o l in g wi l l a l socau se th e KBr p l a t e t o sh a t t e r. O r g an ic so lv en t s su ch a s 1 ,2 - d i ch lo r o b en zen e , t o lu en e , an dd im e th y l f o r m am id e a r e o f t en u sed to ca s t p o ly m er f i lm s . T h e so lv en t u sed i s d ep en d en t u p o nth e p a r t i cu l a r p o ly m er o r co p o ly m er , an d i t s so lu b i l i t y i n t h a t so lv en t .

Si lver ch lor id e p la tes a re o f ten used as the su bst ra te fo r cas t ing f i lms of wa ter - so lu b lep o ly m er s . T h e wa te r i s r em o v ed b y h ea t a f t e r f i r s t p l ac in g th e wa te r so lu t io n o n to th e Ag C1p la t e p l aced u n d e r an I R h ea t l am p . I t i s e s sen t i a l t h a t Ag C1 p la t e s b e s to r ed in t h e d a r k top r ev en t d a r k en in g o f th e p l a t e s d u e to t h e f o r m a t io n o f s il v e r o x id e u p o n ex p o su r e to l i g h t.

I t i s e s sen t i a l t h a t a l l p l a t e s b e c l ean ed a f t e r b e in g u sed in t h e se ex p e r im en t s . T h e p o ly m erf i lm can b e r em o v ed f r o m th e p l a t e s u s in g th e sam e so lv en t s u sed to ca s t t h e f i lm s . I t i s ag a inn ecessa r y to av o id su d d en t em p e r a tu r e ch an g e to t h e p l a t e s d u r in g th e c l ean in g o p e r a t io n inorder to avo id p la te sha t t e r ing in cases such as KBr , NaC1, CaF2 , e tc .

I I I . V A P O R S A N D G A S E SQ u a l i ty I R sp ec t r a c an b e r eco r d ed u s in g p a r t i a l p r e ssu r e s an d ap p r o p r i a t e c e l l l en g th s eq u ip p ed ,s ay , w i t h p o t a s s i u m b r o m i d e w i n d o w s . I t s h o u l d b e n o t e d t h a t c e r ta i n i n o r g an i c c o m p o u n d sr eac t w i th KBr an d f o r m o th e r i n o r g an ic sa l t s o n th e su r f ace o f t h e KBr p l a t e. T h e i r r e ac t io n s a r er ead i ly d e t ec t ed b ecau se th e i r r e ac t io n p r o d u c t s c an n o t b e r em o v ed w h en th e sam p le i sev acu a ted u n d e r v acu u m f r o m th e ce l l .

The IR spec t ra o f chemica ls wi th low vapor p ressure can be recorded using a var iab le long pa thleng th vapo r ce l l e i ther a t ambie n t te mpe ra ture o r a t e leva ted tempera tu re . I t is best i f these var iab lepath leng th ce l l wai ls a re coa ted wi th a substance such as po ly ( te t ra f luoro thy lene) to he lp p reven tadsorp t ion of the chemica l on the sur face o f the meta l l ic ce ll body . It is some t ime s necessary to hea tth e cel l b o d y u n d e r v ac u u m to r em o v e ad so r b ed ch em ica l m o lecu le s . An o th e r m e th o d to c lean o u tadsorbed molecu les p resen t in the ce l l i s to f lush the ce l l wi th n i t rogen or d ry a i r .

I t i s a l so p o ss ib l e t o p e r f o r m q u an t i t a t i v e an a ly s i s o f co m p o u n d s wh o se I R sp ec t r a h av e b eenr eco r d ed in t h e v ap o r p h ase . An o f t en - u sed m e th o d i s t o r eco r d th e p a r t i a l p r e ssu r e o f t h ech em ica l i n t h e v apo r , an d th en b r in g th e to t a l p r e ssu r e u p to 6 0 0 - m m Hg u s in g d r y n i t r o g en .T h e co n s t an t t o t a l p r e ssu r e o f 6 0 0 - m m Hg h e lp s e l im in a te t h e e f f ec ts o f p r e ssu r e b r o ad e n in g o nth e ab so r p t io n b an d s . 1 T h i s r eq u i r e s o f co u r se th a t t h e ap p r o p r i a t e v acu u m l in e an d d r y n i t r o g e nb e av a i lab l e to t h e ch em is t . A lo n g e r p a th l en g th se t t i n g i s r eq u i r ed a s v ap o r p r e ssu r e o f ach em ica l f a l l s . Of co u r se , so m e ch em ica l s r e ac t w i th t h e m i r r o r s , an d th i s w i l l l im i t t h i sap p l i ca t io n f o r t h e se p a r t i cu l a r co m p o u n d s .I t i s p o ss ib l e t o d e t ec t l o w p a r t s p e r m i l l i o n o f ch em ica l s i n a i r u s in g th e v a r i ab l e l o n g p a thce l l s . T h e in t e r p r e t ab l e r eg io n s o f t h e I R sp ec t r u m a r e s ig n i f i c an t ly im p r o v ed b y sp ec t r a l

1The w indows (KBr, NaC1, etc) of mo st glass-bodied cells are adhe red to the glass body by a material suc h as paraffinwax. Pressures higher than 760-mmHg will blow the windows from the glass body. Thus , 600-mmHg sam ple pressure isa reasonable total pressure to safely achieve in these laboratory experiments.


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V a r i a b l e s in D a t a I n t e r p r e t a t i o n 29s ub t r ac t ion o f abs o rp t ion due to the p res ence o f H2 0 and CO2. Th is can be done e lec t ron ica l lyo r by dua l ce l l s p laced in s epara te beam s o f a doub le beam s pec t romete r . I n the cas e o f FT- IRs pec t rome te r s , i t is an eas y t a s k to r emo ve thes e abs o rp t ion bands due to the p res ence o f a ir . In acas e where the re i s no IR r ad ia t ion be ing t r ans mi t t ed in a pa r t i cu la r r eg ion o f the IR s pec t rum,de tec t ion o f a com po und p res en t in a i r (o r in any phas e ) i s no t pos s ib le in thes e s pec t r a l r eg ions ,becaus e the s pec t romete r i s "dead" in thes e r eg ions . S pec t r a l s ub t r ac t ion w i l l no t change the"dead" r eg ions o f the s pec t rum.

A s imple method o f ob ta in ing IR vapor s pec t r a o f chemica l s w i th h igh vapor p res s u re i s toconnec t the s ample con ta ine r u s ing a rubber s toppered hos e to a 0 . 1 -mm (o r 0 . 2 -mm, e tc . )l iqu id ce ll . The s top per i s open ed an d the ch emica l vapor i s a l lowed to f lu s h ou t the 0 . 1 -m m ce ll .The ex i t po r t o f the ce ll is then s toppered , the s ample co nnec t ion i s c los ed and r em oved , an d theen t r ance pa r t o f the ce l l i s a l s o s toppered . The ce l l i s now f i l l ed w i th the s ample in the vaporp h a s e a t a m b i e n t t e m p e r a t u r e a n d p r e s s u r e . O f c o ur s e, t h i s o p e r a t io n s h o u l d b e p e r f o r m e d i n awel l -ven t i l a t ed hood .

G a s c h r o m a t o g r a p h y h a s b e e n c o u p l e d t o i n f r a r e d s p e c t r o s c o p y ( G C / F T - I R ) t o f o r m apowe r fu l ana ly t ica l t echn ique capab le o f s o lv ing ma ny r ea l wor ld p rob lems . T h i s t echn iquerequ i r es tha t the ch romatographed vapor s pas s s equen t ia l ly th rough a go ld -coa ted l igh t p ipehea ted to a t empera tu re o f over 200 oC. The l igh t p ipe pa th - leng th mus t be s ho r t enough s o tha ton ly one ch romatographed componen t i s in the l igh t p ipe a t one t ime . Th i s t echn ique has amajo r p i t f a l l in tha t no t a l l chemica l compounds a r e s t ab le a t the h igh t empera tu res encoun te redu t i l i z ing th i s t echn ique . F o r example , ph tha l i c ac id p res en t a s one componen t in a mix tu rewou ld no t be de tec ted as one o f the ch ro ma togra phe d f r ac t ions . Th i s is becaus e a t thes e e leva tedtempe ra tu res , wa te r s p l i ts ou t o f ph tha l i c ac id to fo rm ph tha l i c a nhyd r ide , wh ich i s theco m po un d de tec ted us ing th i s t echn ique . O ther types o f chemica l r eac t ions can occ ur i f thechemica l s con tac t ho t me ta l s u r f aces ( exc lud ing go ld ) du r ing the i r pa th th rough the GC/F T- IRs ys tem.

In o rder to iden t i fy unequ ivoca l ly a vapor -phas e IR s pec t rum o f a chemica l , an IR vapor -pha s es t a n d a r d s p e c t r u m o f t h i s c o m p o u n d r e c o r d e d u n d e r c o m p a r a b l e c o n d i t i o n s m u s t b e a v a i l a b l efo r com par i s on . T he r eas ons fo r th is a r e p res en ted he re . A co m po un d s u ch as ace t ic ac id ex i s ts a sa h y d r o g e n - b o n d e d c y c li c d im e r i n t h e c o n d e n s e d p h a s e a n d i n t h e v a p o r - p h a se a t t e m p e r a t u r e s150 ~ and below. At e levated tem pera ture , acet ic acid exis ts as isolated CH3C O2H molecu les . Int h i s m o n o m e r i c s t a t e , t h e O H s t r e t c h i n g f r e q u e n c y e x h i b i t s a w e a k - m e d i u m s h a r p b a n d n e a r3 5 8 0 c m - 1 i n t h e v a p o r p h a se , a n d t h e C = O s t r e tc h i n g f r e q u e n c y e x h i bi t s a s tr o n g b o n d n e a r1791 c m - 1 . Thes e f ea tu res a r e un iq ue ly d i f f e ren t f rom the c onde ns ed phas e IR s pec t r a o f ace t icac id . Th i s monomer ic s i tua t ion i s even more compl ica ted in s i tua t ions where in t r amolecu la rhydrogen bond ing can occur be tween the p ro ton o f the ca rboxy l ic ac id g roup and a bas ic s i t e inthe molecu le . F o r example , py ruv ic ac id (2 -oxo-p rop ion ic ac id ) exh ib i t s two bands in the vaporp h a s e a t 9 5 ~ ( 2 ). A w e a k b a n d n e a r 3 5 8 0 c m - 1 i s a s s ig n e d t o an u n a s s o c i a t e d O H g r o u p o fC O 2 H . T h e w e a k - m e d i u m b o n d n e a r 3 4 6 5 c m - 1 r e su l ts f r o m t h e i n t r a m o l e c u l a r h y d r o g e n b o n dOH g roup to the f ree pa i r o f e lec t rons on the ke tone ca rbony l g roup to fo rm a 5 -m em bered cyc li cr ing as i l lus t ra ted here:

o

0 "'" 14


6/6

3 0 ExperimentalO t h e r s i t u a t i o n s o c c u r w h e r e m o l e c u l e s t h a t a r e i n t e r m o l e c u l a r l y h y d r o g e n b o n d e d i n t h e

c o n d e n s e d p h a s e f o r m i n t r a m o l e c u l a r h y d r o g e n b o n d s i n t h e v a p o r p h a s e . I n a d d i t i o n , t h er eg io n s f o r g r o u p f r eq u en c ie s i n t h e co n d en sed o r so lu t io n p h ase s h av e sh i f t ed f r o m th o se in t h ev ap o r p h ase . T h e r e f o r e , o n e m u s t h av e a t h an d a co l le c t io n o f v ap o r - p h ase g r o u p f r eq u en cy d a t a ,av a i l ab l e t o en ab le o n e to i n t e r p r e t t h e se GC/ FT - I R sp ec t r a b y sp ec t r a - s t r u c tu r e co r r e l a t io n s ( 3 ) .A co m p i l a t io n o f t h e v ap o r - p h ase g r o u p f r eq u en cy d a t a h a s b een d ev e lo p ed f r o m ed i to r i a l wo r kp e r f o r m ed b y N y q u i s t o n th e 1 0 ,0 0 0 v ap o r - p h ase sp ec t r a p u b l i sh ed b y Sad t l e r Resea r chLabora tor ies , G. Div is ion of Bio-Rad Labora tor ies , Inc . Th e co l lec t io n of these Sad t le r spec t raa r e a v a lu ab le a s se t f o r t h o se em p lo y in g th e GC/ FT - I R t ech n iq u e to so lv e r ea l wo r ld p r o b lem s .

Ram an sp ec t r a o f sol id s an d l i q u id s a r e r o u t in e ly r eco r d ed u t i l i z in g d i sp e r s iv e o r Fo u r i e rt r an s f o r m sy s t em s .

F o r e x a m p l e , R a m a n s p e c t r a o f l i q ui d e t h y n y l b e n z e n e a n d e t h y n y l b e n z e n e - d w e r e r e c o r d e du t il i z in g a H y l g e r s p e c t r o m e t e r a n d 4 3 5 8 A r a d i a ti o n ( 7 A / m m ) f il te r ed t h r o u g h r h o d a m i n e /n i t r i t e f i l t e r s . Dep o la r i za t io n m easu r em en t s we r e m ad e ( 4 ) . T h ese d ep o la r i za t io n m easu r em en t sa id in d i s t i n g u i sh in g b e tween in - p l an e v ib r a t io n a l m o d es an d o u t - o f - p l an e v ib r a t io n a l m o d es inth e ca se o f e th y n y l b en zen e . T h e in - p l an e m o d es a r e p o la r i zed an d th e o u t - o f - p l an e m o d es a r ed ep o la r i zed .Mo r e r ecen tly , Ram an sp ec t r a o f in o r g an ic s i n wa te r so lu t io n h av e b een r eco r d e d u t i l i z in g th eDi lo r XY Ram an t r i p l e sp ec t r o g r ap h o p e r a t in g in t h e d o u b le su b t r ac t iv e m o d e a n d f i t t ed wi th1 2 0 0 g / m m g r a t in g s . T h e d e t ec to r i s a 3 - s t ag e Pe l t i e r- co o led E G & G s i l ico n CC D m o d e l 1 5 3 0 5e q u i p p e d w i t h a T h o m s o n 1 0 24 x 2 5 6 c h i p, o p e ra t e d a t - 6 0 ~ ( 5) .

Sam p le f lu o r e scen ce l im i t s t h e ap p l i ca t io n o f t h e Ram an t ech n iq u e b ecau se f lu o r e scen ce i s af i r s t - o r d e r p h en o m en o n , an d th e Ram an e f f ec t i s a seco n d - o r d e r p h en o m en o n . T h i s f l u o r e scen cep r o b lem h as b een o v e r co m e r ecen t ly b y th e d ev e lo p m en t o f FT / R am an . I n t h i s c a se, n ea r- I R i su sed a s t h e so u r ce o f ex c i t a ti o n o f th e m o lecu le s . Co ley s h aw et a l . r ep o r t ed o n th e q u a l i t y o f FT -Ram an sp ec t r a a s r e l a t ed to t h e co lo r o f t h e m in e r a l s . T h ey r ep o r t t h a t wh i t e - , g r ay - , y e l lo w- ,p in k - , o r an g e - , an d r ed - co lo r ed m in e r a l s y i e ld g o o d FT - Ram an sp ec t r a , b u t t h ey h ad l i t t l esu ccess w i th b lu e - , g r een - , o r d a r k - co lo r ed m in e r a l s ( 6 ) . T h i s i s b ecau se th e se co lo r s ab so r b r edlight.

A N i c o le t m o d e l 8 0 0 F T -I R s p e c t r o m e t e r / N i c o l e t F T - R a m a n a c c e s s o ry e q u i p p e d w i t h a C a F 2b eam sp l i t t e r , Ge d e t ec to r , an d a CVI m o d e l C- 9 5 N d / YAG la se r c an b e u sed su ccess f u l ly i nr e c o r d in g t h e R a m a n s p e c t r a o f m a n y o r g a n ic a n d i n o r g a n i c c o m p o u n d s . T h e b e a u t y o f t hi sco m b in a t io n d ev ice i s t h a t i t c an b e u sed to r eco r d e i th e r I R o r Ram an sp ec t r a . O th e rm a n u f a c t u r e r s a l s o p r o d u c e F T - R a m a n s y s t e m s .

R E F E R E N C E S1. Po tts, W. J. Jr. (196 3). Chem ical Infrared Spectroscopy, New York: Joh n W iley & Sons, Inc.2. We lti, D. (1970). Infrared Vapor Spectra, New York: Hyd en & Son Ltd.3. N yquist, R. A. (198 4). The Interpretat ion of Vapor-Phase Infrared Spectra: Group F requency Data, vols. 1 and 2,Philadelphia: Sad lter Research Laboratories, Division of Bio-Rad Laboratories.4. Evans,J. C. and N yquist, R. A. (1960). Spectrochim. Ac ta, 16, 918.5. N yqu ist, R. A., Putzig , C. L., and Leugers, M. A. (1997 ). Infrared and R ama n Spectral Atlas o f Inorganic Compoundsand Organic Salts , vol. 1, B oston: Academic Press.6. Coleyshaw, E. E., G riffith, W. P., and B owell, R. J. (199 4). Spectrochim. Ac ta, 50A, 1909.

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