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  • 1. Bi Xun Vng Ha Phn tch cng c 1 PHNG PHP PHN TCH QUANG HC GII THIU V QUANG PH V mt lch s, quang ph (spectroscopy) l mt nhnh ca khoa hc trong nh sng c phn gii thnh cc bc sng thnh phn ca n to ra ph quang hc, l mt th ca mt vi hm ca cng bc x vi bc sng hoc tn s. Hin nay, ngha ca quang ph c m rng bao gm nhng nghin cu khng ch vi cc bc x kh kin m cn vi nhng loi khc ca bc x in t nh tia X, t ngoi, hng ngoi, vi sng v bc x tn s radio. Quang ph ng mt vai tr ct yu trong s pht trin ca thuyt nguyn t hin i. Hn na, cc phng php o ph cung cp nhng cng c c s dng rng ri trong vic so snh cu trc ca cc loi phn t cng nh phn tch nh tnh v nh lng ca cc hp cht v c v hu c. I. Tnh cht chung ca bc x in t Bc x in t l mt dng nng lng m d thy nht l nh sng kh kin v bc x nhit. Nhng loi khc gm tia gamma, tia X, tia t ngoi, vi sng v sng radio. Nhiu tnh cht ca bc x in t c m t mt cch thun tin bi kiu sng hnh sin c in s dng nhiu thng s nh bc sng, tn s, vn tc v bin . Khc vi nhiu hin tng sng khc nh m thanh, bc x in t khng i hi mi trng h tr cho s lan truyn ca n v nh vy n c th i qua mt mi trng chn khng. M hnh sng tht bi trong vic gii thch nhng hin tng gn lin vi s hp th v bc x ca nng lng bc x. hiu nhng qu trnh ny cn thit phi nh n mt m hnh kiu ht trong bc x in t c xem nh l mt dng ht ri rc gi l photon, vi nng lng ca mt photon t l vi tn s ca bc x. Quan nim v lng tnh sng ht ny ca nh sng khng loi tr ln nhau m c tnh cht b sung cho nhau. Thc vy, lng tnh ny c thy trong nhng dng electron v nhng ht c bn khc nh proton v c hon ton l gii bi c hc sng. 1. Cc tnh cht ca bc x in t V nhiu mc ch, bc x in t c biu din mt cch thun li nh nhng trng in t tri qua cc dao ng pha hnh sin (hnh). y ta ch xem xt thnh phn in ca bc x bi v in trng chu trch nhim cho hu ht nhng hin tng ta quan tm nh s truyn qua, phn x, khc x v hp th. Tuy nhin, iu ng ghi nh l thnh phn t trng ca bc x in t chu trch nhim cho s hp thu cc song tn s radio trong cng hng t ht nhn.

2. Bi Xun Vng Ha Phn tch cng c 2 2. Cc thng s sng Bin A ca sng hnh sin c xem nh chiu di ca vect in trng ti cc i ca sng ny. Thi gian (giy) c i hi cho mt khong hai cc i hoc cc tiu lin tip thng qua mt im c nh trong khng gian c gi l chu k p ca bc x. Trong mi trng cha vt cht th s lan truyn ca bc x b chm hn do s tng tc gia in trng ca bc x vi in t ngoi cng ca nguyn t hoc phn t. Tnh cht sng ca nh sng c m t bi hai i lng tn s v bc sng. Tn s l s dao ng ca in trng trong mt giy, n v ca n l S-1 hay cn gi l Hertz. Bc sng l khong cch gia hai im cc i hoc cc tiu lin tip ca sng, thng c biu din theo mt (m) hoc nanomet (nm) cho nhng bc sng rt ngn (1nm = 10-9 m) hoc Ao (angstrongs, n v khng thuc h SI, 1 Ao = 10-10 m) . Vn tc ca tt c bc x in t trong chn khng (trong khng kh nh hn 0.03%) u bng tch ca tn s v bc sng ca n: C = = 3.00 x 108 m/s C cn gi l vn tc ca nh sng. V d: Mt i pht thanh pht sng c bc sng bng 325 cm. Hi tn s ca bc x in t ny. Gii: = C/ = 3.00 x 108 m/s/(325x10-2 m) = 9.23 x 107 s-1 S sng c nh ngha nh nghch o ca bc sng (cm) l mt cch khc m t bc x in t. Th nguyn ca s sng l cm-1 . S sng tin ch v ngc vi bc sng, n c s dng rng ri trong ph hng ngoi. N l i lng rt tin li v tri vi bc sng n t l thun vi tn s tc vi nng lng ca bc x. Nh vy ta c th biu din: = k y k l hng s t l ph thuc vo mi trng v bng nghch o ca vn tc. V d: tnh s sng ca bc x hng ngoi c bc sng 5.00m. 3. Bi Xun Vng Ha Phn tch cng c 3 = 1/(5.00x10-4 ) = 2000 cm-1 3.Tnh cht ht ca bc x Nm 1900, gii thch bc x ca vt en (blackbody radiation) khi b nung nng Planck ra thuyt lng t. Theo thuyt ny bc x c pht ra hay hp th nhng lng gin on ca nng lng hay cc lng t nng lng. Trn c s thuyt lng t Planck, Einstein xut thuyt photon ca nh sng gii thch hiu ng quang in; theo nh sng c xem nh chm ht photon. Nng lng ca mt photon ph thuc vo tn s v vo bc sng ca bc x: = h = hc/ vi h l hng s Planck = 6.626x10-34 J.s V d : tnh nng lng di dng jun ca mt photon ca bc x c to ra trong mt l vi sng c bc sng bng 12.0 cm = hc/ = 6.626x10-34 x 3.00x108 / (12 x 10-2 ) = 1.66 x10-24 J 4. Biu thc thng nht lng tnh sng ht ca nh sng nh sng l mt dng ca vt cht v nh vy theo thuyt tng i ca Einstein mi photon c xem nh mt ht c khi lng m v phng trnh biu din mi quan h gia vt cht ( y l photon) vi nng lng l: = mc2 Mt khc ta c: = h. Nh vy = h = mc2 Theo tnh cht sng ca nh sng th: c =. Vi vi bin i n gin ta rt c biu thc hay cn gi l biu thc thng nht lng tnh sng ht ca nh sng: = h/mc II. Ph bc x in t Quang ph ca bc x in t bao gm mt di rt ln cc bc sng (v l nng lng). Trong phn ca bc x kh kin m mt ngi c th thy c l rt nh khi so vi nhng vng ph khc. Cng cn phi ch l cc phng php quang ph s dng khng ch vng kh kin m cn 4. Bi Xun Vng Ha Phn tch cng c 4 t ngoi, hng ngoi v thng c gi l phng php o quang mc du mt ngi khng nhy vi hai loi sau. Bng lit k cc di bc sng v tn s ca nhng vng ph quan trng trong mc ch phn tch v cng km theo tn ca nhng phng php ph lin quan. Cc ct cui cng lit k cc loi chuyn dch lng t ca ht nhn, nguyn t v phn t, l c s cho cc k thut quang ph khc nhau. Loi quang ph Di bc sng Di s sng(cm-1 ) Kiu dch chuyn lng t Pht x tia gamma Nhiu x, hunh quang, pht x, hp thu tia X Hp thu t ngoi chn khng Hp thu, pht x v hunh quang t ngoi kh kin Hp thu hng ngoi Hp thu vi sng Cng hng t spin Cng hng t nhn 0.005 1,4 Ao 0.1-100 Ao 10-180 nm 180-780 nm 0.78-300 m 0.75-3.75 mm 3 cm 0.6-10 m - - 1 x 10 6 n 5 x 104 5 x 10 4 n 1.3 x 104 1.3 x104 n 3,3 x 101 13-27 0.33 1.7x 10-2 n 1 x 103 Ht nhn Electron bn trong Cc electron lin kt Cc electron lin kt Dao ng iu ha/quay ca phn t Dao ng quay phn t Spin ca electron trong t trng Spin ca ht nhn trong t trng 5. Bi Xun Vng Ha Phn tch cng c 5 Chng 1: PH HP TH PHN T UV-VIS 1.1.S hp th phn t UV-VIS Cc phn t iu kin bnh thng tn ti trng thi c bn bn vng c nng lng thp. Khi chng c cung cp nng lng, v d nh c ngun sng kch thch tn s thch hp, th cc in t ha tr (lin kt) trong phn t s hp th nng lng ca ngun sng v chuyn ln trng thi kch thch c nng lng cao hn. Theo c hc lng t, trong phn t trng thi c bn, cc in t c xp y vo cc orbitan lin kt , hoc cc cp electron ha tr cha tham gia lin kt n c mc nng lng thp (v d cc nguyn t N cn mt cp electron ha tr cha tham gia lin kt). Nu chiu vo chng chm sng c bc sng v thch hp th chng s chuyn ln cc obitan phn lin kt c mc nng lng cao hn nh *, * , n *, n *. Trng thi ny gi l trng thi kch thch, n khng bn ch tn ti trong khong thi gian rt ngn (c phn triu giy). Nng lng h ca photon ng bng hiu ca hai mc nng lng ca hai obitan. S dch chuyn ca mt electron gia hai obitan c gi l s dch chuyn in t (electron transition) v qu trnh hp thu c gi l s hp th in t. Cng vi s chuyn dch in t th cc phn t th hin hai loi khc ca s dch chuyn cm ng bc x l s dao ng v quay. Nhng dch chuyn dao ng to ra v mt phn t c mt s mc nng lng c lng t ho gn vi nhng lin kt gia cc phn t. Hnh 1 l s mc nng lng m t mt vi qu trnh xy ra khi mt phn t hai nguyn t khc nhau hp thu bc x t ngoi kh kin, trong nng lng trng thi kch thch in t u tin En ca phn t c biu din tng i so vi nng lng ca trng thi c bn Eo. Ngoi ra, cc mc nng lng tng i ca mt vi trng thi dao ng v rt nhiu cc trng thi nng lng ca dao ng quay nh hn cng c th hin trn s ny (cc ch s 0,1,2..., vi gi tr 0 c biu din cho mc nng lng dao ng hoc quay nh nht). Nng lng tng cng E vi ca mt phn t c vit nh sau: E = Ein t(e) + Edao ng(d) + E quay(q) y: Ein t(e) l nng lng ca cc electron trong cc obitan lp v ca phn t, Edao ng(d) l nng lng cc dao ng gia cc nguyn t trong ton b phn t, Equay(q) l gii thch cho nng lng lin quan vi s quay ca phn t quanh trng tm ca chng. Gi s nng lng ca mt phn t trng thi c bn c biu din l Eo, cn trng thi kch thch l En th hiu hai mc nng lng ca phn t hai thng thi ny ng bng nng lng h ca photon: E = En Eo = E(e) + E(d) + E(q) = h =hc/ Trong E(e) > E(d) > E(q) Nh ch ra trong hnh 2, s hp th phn t trong vng t ngoi kh kin gm nhng di hp th c to do rt nhiu vch c khong cch rt gn nhau, dn n ph UV-VIS khng phi l ph vch nh ph pht x hoc hp th nguyn t m l ph m. Nh vy ph hp thu phn t UV-VIS l ph xut hin do s tng tc ca cc in t ha tr trong phn t hay nhm phn t vi chm sng kch thch c bc sng nm trong vng UV-VIS to ra. 6. Bi Xun Vng Ha Phn tch cng c 6 Hnh 1: Cc mc nng lng in t, dao ng v quay (khng theo t l) ca hai mc nng lng in t u tin ca phn t hai nguyn t (v d CO). Hnh 2: Ph hp th phn t ca mt vi hp cht hu c (ph m) v ph hp th nguyn t Na (ph vch). 1.2.nh lut Beer 1.2.1. nh lut Nu ta chiu mt chm sng n sc c cng Io vo mt cuvet cha dung dch cht mu c di l l th mt phn chm sng i qua cuvet, mt phn phn x v tn x ra cc phng do va p vo thnh cuvet v mt phn b cc phn t trong cuvet hp thu. Trong phn hp th bi cc phn t cht mu trong cuvet l chnh. 7. Bi Xun Vng Ha Phn tch cng c 7 Nu sau khi i qua cuvet cng nh sng cn l I th ta c s hp th nh sng n sc ca cc phn t trong cuvet c biu din bi: i lng mt quang D = log(Io/I) hay truyn qua T = (%)100x I I o Theo nh lut Beer: D = LC y: l h s hp thu phn t (L.mol-1 .cm-1 ) L l chiu di ca dung dch nh sng i qua (cm) C l nng ca cht hp thu (mol/L) 1.2.2. p dng nh lut Beer trong dung dch hn hp nh lut Beer cng c p dng cho dung dch cha hn mt loi cht c th hp th c nh sng chiu qua. Nu khng c s tng tc gia cc cht, mt quang ca dung dch c cho nh sau: D tng = D1 + D2 + . + Dn = 1LC1 + 2LC2 + + nLCn y cc ch s 1,2,,n ch cc cht th 1,2,, n. H qu: D dung dch mu = Dcht mu + Dso snh Dso snh l mt quang ca dung dch trng (blank). Dung dch ny c chun b sao cho c thnh phn nh dung dch mu o nhng khng cha cht mu. 1.2.3. Cc yu t nh hng n nh lut Beer a. nh hng nng : nh lut Beer ch ng trong trng hp nng cht phn tch tng i thp. Ti nhng nng cao (thng ln hn 0.01M) khong cch trung bnh gia cc phn t cht tan hp th nh sng b thu hp ti mc tc ng n s phn b in tch ca cc phn t xung quanh. iu ny lm thay i kh nng hp th bc x n sc, dn n lm sai lch mi quan h tuyn tnh gia A v nng C ca cht hp thu bc x . nh hng tng t cng thnh thong xy ra khi trong dung dch mu o c cha nng cht cn o thp nhng cha nng rt cao cc loi khc, c bit l cc cht in ly. S tip cn ca cc ion n cht hp thu lm thay i h s hp thu phn t do tng tc tnh in. nh hng ny c th gim thiu bi s pha long. lch ca nh lut Beer