Pho Hong Ngoai IR

7/30/2019 Pho Hong Ngoai IR

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Chng1.PH HNG NGOIInfrared (IR) spectroscopy


2/19

1. C s l thuyt:


3/19

Nng lng lng t (ca photon nh sng) c xc nh bicng thc sau y:

h: hngs Planck, 6.6 x 10-34 (J/s)c: tcca nh sng trong chn khng, 3 x 1010 (m/s)

: bc sng (m): tns (s-1 hoc Hz)

Thng thng th n v ca bc sng c s dng trong ph hngngoi l m ( 1 m = 10- 4 cm) v thay cho tns (Hz), ngi ta sdngnv l s sng:


4/19

3. Ktqucbiudinbngthca hm snnglng sng

inti qua phthuc vo bc sng.Trc honh biudinbc

sng vingnm ngang trn nv l m; ngnm ngang

dinv l s sng (cm-1), trc tung l hshpth sng in

t c nv l %.

1. Khi phn thpchthucvachmvi chm sng ints

hp thu mtnng lng tngngvibc sng xc nh no

catia

tiv khng

hpthu cc chm tia c

bcsng khc.

2. Nu ta chiumuchthucmt

sng in t vi cc bc sng

khc nhau v sau xc nh xem

bc sng no b hp thu, bcsng no khng th chng ta s c

cmtphhp thu camu.


5/19

Vng bcxhngngoi (IR) l mt vng phbcxintrng

nmgia vng trng thy v vng vi ba; vng ny c th chia thnh

3 vng nh:

- Near-IR 400-10 cm-1 (1000- 25 m)

- Mid-IR 4000 - 400 cm-1(25- 2,5m)

- Far-IR 14000- 4000 cm-1(2,50,8m)

Phng php phn tch phhngngoi ni y l vng phnm

trong vng c s sng 4000 - 400 cm-1.

Vng ny cung cp cho ta nhng thng tin quan trngv cc dao

ngca cc phn t do l cc thng tin vcu trc ca cc

phn t


6/19

iukinhpthbcxhngngoi:

c thhpthbcxhngngoi, phn tphipngcc yu cu sau:

- di sng chnh xc cabcx: mt phn thpthbcxhngngoich khi no tns dao ngt nhin camtphnphn t (tc l cc nguyn t hay cc nhm nguyn t tothnh phn t) cng l tnscabcxti.

-Mt phn tchhpthbcxhngngoi khi no shpth gy nn sbin thin momen lngccca chng.


7/19

Lngccin:Mt phn tchhpthbcxhngngoi khi no shpth gy nn sbinthin momen lngccca chng.Khi phn t lngcccgi trong mtin trng, trngs tc dng

cc lc ln cc in tch trong phn t - Cc in tch ngc nhau schu cc lctheo chiungc nhau, iudnns tch bit 2 cctnghocgim.V intrngcabcxhngngoi lm thay i phn ccca chng mtcch tun hon, khong cch gia cc nguyn t tch inca phn tcng thayimt cch tun hon.Khi cc nguyn t tch in ny dao ng, chng hpthbcxhngngoi.

Nuvntc dao ngca cc nguyn t tch in trong phn tln, shpthbcxmnh v s c mphhp thmnh, ngc linuvn tc dao ngca cc nguyn t tch in trong phn tnh, mphhpthhngngoiyu.Theo iukin ny th cc phnt c 2 nguyn tging nhau s khng xuthinph dao ng. V d O2, N2 v.v khng xuthinphhp thhngngoi. cng l mtiu may mn, nu khng ngi ta phiuiht khng kh ra khi

my quang phkhngngoi.


8/19

Trng thi dao ngca phn t 2 nguyn t:Gis 2 nguyn t A v B tc dngvi nhau to thnh phn t AB. Gi r lkhong cch gia hai nhn ca nguyn t A v B, r l khng phi khng i

m nhngiukin xc nhs dao ngt gi trnhnht rminn gi trlnnht rmax. T rmin sang rmax, r c i qua gi tr cn bng r(e), l gi tr c xcsut lnnhtca r. Ngi ta ni phn t AB thchinchuynng daongniti .Khi ko dn AB hoc nn AB th s c s thay i r cn bngca AB trngthi bnh thng. S chnh lch rgi l r. Lc sxuthin 1 lc F ko

AB vv tr cn bng. F gi l lchiphc v F tlvidchchuynr.F = - k. r(k: hngslc, dyn/cm)Nu r rt b, chuyn ng dao ng l dao ng iu ho.Vmtchc, c th coi dao ngca 2 vtth A, B nh 1 khi thu gn ckhilngm dao ng quanh v tr cn bngvitns dao ng ring l:


9/19

C th minh ho cc kiu dao ng co gin lin kt v dao ng bin dng caphn t nc theo m hnh di y :
http://localhost/var/www/apps/conversion/tmp/scratch_8/Infrared%20spectroscopy%20-%20Wikipedia,%20the%20free%20encyclopedia.htm


10/19

Hai nguyn t v lin ktni chng vi nhau c coi l mt dao ngkngin bao gm hai khi lng lin kt vi nhau bng mt l xo. T nh lutHooke, ta c thnhncphng trnh sau y :

f: hng s lc lin kt (Ni n f = 5.105dyn/cm; Ni i f = 10.105 dyn/cm;Ni ba f = 15.105 dyn/cm)

mH = 1 / 6.02.1023

mC = 12 / 6.02.1023


11/19

1.2. Tng quan gia ph dao ng v cu trc phn t

Cc nhm chc, nhm nguyn t v lin kt trong phn t c cc

m ph hp th hng ngoi c trng khc nhau .

Mc d phng php ph dao ng l mt trong nhngphng php huhiunht xc nh

cc chtvnh tnh cngnhnh lng,cngdngrng ri trong nghin cu khoa hccngnh trong kim tra cng nghip,phng php ny cng c nhnghnchnhtnh:- Bngphng php phhngngoi khng cho bit phn tlng(trtrnghpcbit).-Ni chung phhngngoi khng cung cp thng tin v cc v tr tngica cc nhm chckhc nhau trn mt phn t.- Chring phhngngoi th i khi chathbit l cht nguyn cht hay chthnhp v ctrnghp 2 cht c phhngngoiging nhau.


12/19

1.3. ng dng :

1. Nhnbit cc cht - Trc khi ghi phhngngoi, ni chung ta

c th c nhiu thng tin vhpchthochnhpcn nghin cu,

nh: trng thi vt l, dng bn ngoi, tan, im nng chy,imchy.

Nu c th th cnbitchcmu l cht nguyn cht hay hnhp.

Sau khi ghi phhngngi,nucht nghin cu l hpchthuc

th trc tin nghin cu vng dao ng co gin ca H xc nhxem mu thuc loi hp cht vng thm hay mch thng hoc c

hai. Sau nghin cu cc vng tn s nhm xc nh c hay

khng c cc nhm chc.

Trong nhiu trng hp vic c ph (gii ph) v tm cc tn s

ctrng khng nhnbitmt cch ton dinvcht nghin

cu,nhng c l l c th suy onckiuhocloihpcht.

2. Xc nh tinh khit.

3. Phn tch nhlng.


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Pho Hong Ngoai IR