Joarder, R N

Krishna P, S R

IACS Institutional Repository

Indian J. Phys. 75A (1). 95-96 (2001)U P  A— an international journalH-bonded clusters in liquid ter-butanol through neutron diffractionP  S R  Krishna*' and R N[ Joarder^’*“Condensed Matter Physidi Division.Bhahha Atomic Research Centre. Mj|inibai-4()() OK.S. India '’Dcpartincnt of Physics, Jadavpui Univcrsily, Cakima-700 032. IndiaE-mail rnjC«'iuphys4rnet inAbstract : In the liquid state at room temperature, the neutron diffraction dlia ot deuterated t bulanol exhibits a promineni pre peak similar to what is known for long in the X-ray diffraction data with normal t-butanol Thif pre-peak is interpreted as a signature of hydrogen-bonded chain hexamer nng clusters in the liquid state.Keywords H-bonded clusters, neutron diffraction, t-butanol PACS Nos. 6112 -q. 61 25 -f1. IntroductionA lc o h o ls  a rc  s t r o n g ly  h y d r o g e n - b o n d e d  l iq u id s  w h e re  ne ighbouring  m o lecu le s  fo rm  ch a in  c lu s te rs . It is now  know n that the ch a in  h y d ro g e n -b o n d e d  c lu s te rs  in these  liq u id s co u ld  give rise to  w h a t is ca lled  a p re -p eak  in the  sta tic  d iffrac tio n  d a ta  at sm all sca tte r in g  v e c to r (Q  ~ 0 .7  - 0 .8  A *) b efo re  the m ain  d iffraction  peak  [I -  3]. In X -ray  d iffrac tio n  d a ta , these  p re- peaks a re  k n ow n fo r long , w h ile  in n eu tro n  d iffrac tio n  d ata , these are d e tec ted  o n ly  recen tly  |2 , 41. In the  p re sen t case , w e report the  e x is ten ce  o f  su ch  a  p re -p eak  in n eu tro n  d a ta  o f  liqu id  t-butanol a t ro o m  tem p era tu re . T he  c lu s te r  m o d el o f  H -b o n d ed  closed h ex am e r c h a in s , seem s to  p ro d u ce  w ell the  p re -p eak  in the X -ray  d a ta  o ff -b u ta n o l [5] and  so  rep resen ts  w ell the  average l iq u id  s t r u c tu r e  a t  r o o m  t e m p e r a t u r e .  In  th e  p r e s e n t  co m m u n ica tio n , a  p re lim in a ry  an a ly s is  o f  first n eu tro n  d a ta  on deu tera ted  liq u id  t-b u tan o l is rep o rted .2. ExperimentalA careful m easu rem en t w as c arried  ou t on  h igh -Q  d iffrac to m eter at D hruva, B h ab h a  A to m ic  R esearch  C en tre  (B  A R C ), T rom bay, India fo llo w in g  th e  c o n v e n tio n a l p ro ced u re . T h e  liqu id  w as a 99.8%  d e u te ra ted  sam p le  su p p lie d  by  A ld rich  L td . (U S A ) and was held in  vanadium  can  o f  6  m m  diam eter and 0.1 m m  thickness. The d a ta  co llec tio n  and  e x p e rim e n ta l c o rre c tio n s  w ere  d o n e  in usual m an n e r an d  th e  c ro ss -se c tio n  d a ta  w ere  n o rm a lized  using  a standard  v an ad iu m  ro d . T h e  in c id e n t w av e len g th s  o f  0 .7 8 3  ACorresponding author.and  1.278 A w ere used  and the d a ta  w ere reco rded  for an angular ran g e  3^ ' to  125 ‘\  T h e  d a ta  show  a very stro n g  p re-peak  at about Q  =  0.71 A ‘ (F ig u re  1) T he inset e x h ib its  N a rten ’s X -ray  data [3]. T h e  co m p le te  se t o f  co rrec ted  data  is now  av ailab le  and deta iled  analysis o f  m o lecu lar structure, w hich w ould be reported separa te ly , y ie ld s  n eu tron  to tal stru c tu re  fucn tion  H (0 )  show n in F igure 2(a).Figure 1. intensity r.v. Q plot 3. Inteipretalion of pre-peakT he in terp re ta tion  o f  the p re-p eak  in term s o f  F o u rie r T ransfo rm  (F. T .) o f  the d iffrac tion  d a ta  is d ifficu lt in v iew  o f  the  fact tha t it©2001 lACS96 P S R Krishna and  R N  Joarderg iv e s  so m e  m o d if ic a tio n  in  th e  c o r re la t io n s  a t d is ta n c e s  5 - 8  A  an d  d e f in ite  fe a tu re s  a r is in g  fro m  th e  p re -p e a k  a re  d if f ic u l t  to  s e p a ra te  a n d  c le a r ly  id e n tify  [11, H o w e v e r , an  in te rp re ta tio n  in te rm s  o f  th e  m o le c u la r  c h a in  c lu s te r  fo rm a tio n  m o d e l is re a d ily  p o s s ib le . T h e  th e o ry  o f  m o le c u la r  c h a in  c lu s te r  fo m ia lio n  d u e  to  h y d ro g e n  b o n d in g  h a s  b e e n  d is c u s s e d  in s e v e ra l  r e c e n t  p a p e rs  16 ) a n d  it is n o t re p e a te d  h e re . In  th e  th e o ry  o n e  a s s u m e s  th a t (1 )  th e re  e x is t d i.s tinct m o le c u la r  c lu s te r  o r  c lu s te rs  in th e  liq u id  d u e  to  h y d ro g e n  b o n d in g  a n d  th a t ( i i)  th e  m o le c u le s  in d iffe re n t c lu s te rs  a rc  o r ie n ta tio n a lly  u n c o rrc la tc d . A ssu m in g  th a t fo r  a  la rg e  m o le c u le  lik e  t-b u la n o l th e  c e n tr e  s tru c tu re  fa c to r  o f  th e  liq u id  can  be a p p ro x im a te ly  reprc.scn lcd  by  th e  P ercu s-Y cv ick  (P Y ) s in g le  s ite  h a rd  sp h e re  m o d e l w ith  su i ta b le  c o re  d ia m e te r  w e can  c o n s tru c t th e  m o d e l s tru c tu re  fu n c tio n  o f  th e  l iq u id  fo r  a n y  m o d e l c lu s te r .T h e  X -ra y  d a ta  w a s  c h e c k e d  fo r  tw o  w id e ly  s u g g e s te d  m cxiels -  a  c lo se d  c h a in  h e x a m e r  an d  a  lin e a r c h a in  te tram er. T lie  h e x a m c r  c h a in  m o d e l w a s  sh o w n  to  b e  m o re  p ro b a b le  b o th  in te rm s  o f  to ta l s t r u c tu r e  fu n c t io n  a n d  m tc r m o lc c u la r  ra d ia l  d is tr ib u tio n  fu n c tio n  (R D F )  |5 ) .  A  m o re  c r i t ic a l  a n a ly s is  o f  h e x a m e r  r in g  c lu s te r  m o d e l a s  a  p la u s ib le  m o d e l fo r  t-b u ia n o l l i q u i d  s t r u c t u r e  in  t e r m s  o f  a s y m m e t r i c a l  p a r t  o f  th e  in tc n n o lc c u la r  co rre la tio n  is p re sen ted  in a  recen t c o m m u n ic a tio n  17|. F o r th e  in te rp re ta tio n  o f  p re -p e a k  in  n e u tro n  d a ta  w e  h a v e  c o n s tru c te d  h e x a m e r  c lo s e d  c h a in  c lu s te r  m o d e l s im ila r  to  o n e0.200 10 oX-0 00- 0.10- 0.20(a)^ /V  ■7 \ .7  . . .Hexamer ring cluster model Experimental neutron data ■ (Jncorrelated model0101 2Q (A ’)Figure 2. Total structure function I'.v. Q plot- - 0.00- - 0.100.200.30fo r X -ray  da ta . In th e  p re lim in a ry  c a lc u la tio n  fo r th e  m o d e l cluster, w e  h a v e  a s s u m e d  m e th y l  g r o u p  C D ^  a s  a s in g le  u n it w iih s c a t t e r in g  le n g th  a s  s u m  o f  th e  s c a t t e r in g  le n g th s  o f  its c o n s t i tu e n ts  w ith  th e  s c a t te r in g  c e n tr e  lo c a te d  su ita b ly . F o r  the h a rd  sp h e re  c e n tr e  s tru c tu re , th e  h a rd  c o re  d ia m e te r  is ch o sen  to  b e  5 .1 0  A  s o m e  w h a t g re a te r  th a n  th a t fo r  th e  X -ra y  c a se  [5 | W h e n  th e  h e x a m e r  c lu s te r  p a ra m e te r s  a re  su i ta b ly  a d ju s te d  n m o d e l s tru c tu re  fu n c tio n  o f  th e  fo rm  s h o w n  in  F ig u re  2{b) is g e n e ra te d .  T h e  p re - p e a k  is  e v id e n t  a n d  th e  g e n e ra l fea tu res  a g r e e .  F o r  c o m p a r is o n ,  w e  a ls o  s h o w  th e  c a s e  w h e re  the n e ig h b o u r in g  m o le c u le s  a rc  u n c o r r c la tc d  a n d  a s  e x p e c te d  the p re -p e a k  a n d  th e  o th e r  fe a tu re s  h a v e  d is a p p e a re d .In  v ie w  o f  v e ry  g o o d  a g re e m e n ts  w ith  X -ra y  d a ta  [5 , 7], we e x p e c t  m u c h  b e lte r  a g re e m e n t fo r  n e u tro n  d a ta  to o . F u rih c i a g re e m e n t h o w e v e r  a w a its , (a )  D e ta ile d  c o n s id e ra t io n  o f  the s tru c tu re  o f  th e  h e x a m c r  c lu s te r  m o d e l fo r  n e u tro n  sc a tte r in g  b e c a u se  m e th y l g ro u p  CD^ c a n n o t b e  tr e a te d  as  a  s in g le  u n it as in  X -ra y  (C H ^ ), (b )  T h e  p re s e n c e  o f  f r a c tio n s  o f  o th e r  p o ss ib le  m o d e l c lu s te r s  a n d  (c )  C o m b in e d  a n a ly s is  b a se d  o n  X -ra y  and n e u tro n  d a ta . W o rk s  o n  th e s e  lin e s  a rc  in  p ro g re ss . It is, h o w ev e r tru e  th a t th e  n e u tro n  d if f ra c t io n  d a ta  to o  s u p p o r ts  th e  id e a  that th e  l iq u id  t-b u ta n o l s t ru c tu r e  at ro o m  te m p e ra tu re  is d o m in a te d  by  th e  p re s e n c e  o f  h e x a m e r  r in g , c lo s e d  c h a in  u n its .AcknowledgmentsT h e  a u th o rs  a re  g ra te fu l to  lU C -D A E l*  fo r f in a n c ia l su p p o rt T h a n k s  a rc  a ls o  d u e  to  D r. S . S a rk a r  a n d  S ri P. P. N a th  fo r  u sefu l a s s is ta n c e .R eferencesn i  A H  Narten and A Hahcnchuss J. Chrm Plt\s 80 (1984)(21 P Zettcrslroni, U Dahlborg and W S Howells Mol, PHyk 81 1187 (1994)[3] A H Nartcn and S 1 Sandler J Chan. Phvs. 71 2069 (1979)14] A K Karmakar. P S R Krishna and R N Joarder Phy.s I^tt A253 207 (1999)[.SI A K Karmakar. S Sarkar and R N Joarder./ Phys Chem 99 16501 (1995)(6j S Sarkar and R N Joarder J Chem. Phys. 99 20,32 (1993) ; A K Karmakar and R N Joarder Phys. Rev B47 4215 (1993)|7J S Sarkar P P Nath and R N Joarder Phy.\ Lett. A 275 138 (2000)

H-Bonded Dusters in Liquid Ter-Butanol Through Neutron Diffraction

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H-Bonded Dusters in Liquid Ter-Butanol Through Neutron Diffraction

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