emission of light by atoms - kilby利用原子-基尔比光发射

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1、THEBOHRMODELANDTHEATOMICSPECTRUMOFHYDROGEN(Zumdahl,pp.284-290)Everyoneknowsthatwhitelightisn’treallywhite;itisacompositeofa“rainbow”ofcoloursthatblendintooneanother.Ifwetakewhitelightandsplititupusingaprism,weforma“continuousspectrum”ofcolour.Inthiscontinuousspectrum,eachcolouroflighthasadi

2、fferentamountofenergy;redlightismuchlessenergeticthanvioletlight.(http://seco.glendale.edu/astronomy/hp/pix/ce-continuoussplabeled.jpg)Ifwetakeatomsand“excite”(causetheelectronsto“jump”)thembyusingahighelectricalvoltage,lightisproducedbythegas.Ifwelookatthislightthroughadevicecalledaspectro

3、photometer,wecanseethespectrumoflightformedbythatparticulargas.Insteadofacontinuousbandofcolour,youshouldnoticeasmallnumberofverysharpbandsofcolourseparatedbyblackspace.Thistypeofspectrumiscalleda“linespectrum”(inthiscaseanemissionspectrum)andshowsusthatthelightcomingfromthegasesismadeupofo

4、nlyafewdifferentenergies.(http://www.pas.rochester.edu/~afrank/A105/LectureVI/FG04_003_PCT.gif)Howaretheselinespectraproduced?In1911,NielsBohrhypothesizedthattheelectronsinatomstraveledaroundthenucleusinorbitsthatwerefoundatfixeddistancesfromthenucleus.Eachoftheorbitsalsocorrespondedtospeci

5、ficlevelofenergy.Theorbitclosesttothenucleuswascalledn=1,thenextn=2,thenextn=3andsoon.Thelowestorbit(theoneclosesttothenucleus)wasalsocalledthe“groundstate”orbitandrepresentedthelowestenergystate.Asthe“n”numberincreased,theamountofenergyassociatedwithitalsoincreased.Bohr,instudyingthespectr

6、umgivenoffbythehydrogenatom,thoughtthatanelectroncouldjumpfromoneenergyleveltoanotherifitabsorbedoremittedjusttherightamountofenergy.Inorderforanelectronto“jump”toahigherorbit,ithadtoabsorbenergyfromheatorelectricity.Inthishigher(“excited”)state,theelectronwasunstableanditwouldeventuallyfal

7、ldowntoitsregularorbit.Infallingbackdown,theelectronreleased(emitted)theenergythatithadabsorbedintheformoflight.Thisamountofenergycorrespondedtoaspecificcolouredbandinthespectrumforhydrogen.Unfortunately,Bohrcouldnotexplainthespectraofelementsotherthanhy