The power of analytical spectroscopy

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Geraldine Campbell
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1 The power of aalytical spectroscopy Daiila et al. J. Rama Spectr. 33, 807 (00) Reflected light Red lake varish UV light Rama spectrum Lead white ciabar Caput mortuum Byzatie Ico (AD Our 534), Lady, Our i X-rays UV Lady, light the Life-givig Sprig

2 .. Basic Priciples of Atomic Physics xtremely simplified quatum mechaical model of the atom is the Bohr model based o Rutherford scatterig experimets. Negative electros are boud by electric (Coulomb) attractio to positive ucleus excitatio de-excitatio The atomic ucleus: positive charge: C atomic mass: ~ A g miiscule size: ~ cm L M N The electro orbits: egative charge: C egligible mass: ~ g fair size: ~ cm Oly certai orbits for electros are allowed: quatum states are characterized by certai radius ad eergy state, oly limited umber of electros allowed per quatum state

The Hydroge Atom http://www.walter-fedt.de/ph4e/bohrh.htm http://www.falstad.com/qmatom/ l Z 0 ev 0 36.

3 The Hydroge Atom l Z 0 ev is eergy ecessary to ioize atom Z 0 is charge of ucleus, Z mai quatum umber l - orbital mometum quatum umber l0 l0

4 Mathematics of Quatum Trasitios Hydroge atom: sigle proto i ucleus, sigle electro i orbit r [ m] 9 lectro orbit radius [ ev ] 34,,,... lectro orbit eergy lectro trasitio betwee orbits requires or releases eergy: ergy comes quatized as light particles: photos ev J

5 Trasitio betwee ergy Orbitals Possible emissio or absorptio of light with fixed wavelegths by trasitios of electros betwee orbits! Wavelegth depeds o eergy differece betwee orbits! Hydroge emissio spectrum Balmer Series -3.6/

6 ergy ad wavelegth of emitted or ν ν absorbed light photos 3.6 i f f i h c 3.6 h ν h c λ λ f i [ ev ] [ ev ] 34 h Plack Costat: [ Js] c Speed of Light: [ ev ] c h [ m/ s] m R H

7 xamples Calculate the wavelegth of a photo emitted by a electro trasitio i the hydroge atom from the L-shell ( ) to the -shell ( ) (Lyma-series L α )! λ R H f λ i R H m.5 m :.097 wavelegth 0 7 [ / m] 0.75 I iterstellar space you fid highly excited hydroge atoms which emit radio waves. The wavelegth correspods trasitio from 73 to 7. Calculate the wavelegth! RH R H λ f i 7 λ 0.93 m : radio wavelegth [ / m]

8 Wavelegth rage i the electromagetic spectrum The wavelegth rage exteds from 0-5 m (γ-radiatio) or 0-9 m (X-ray radiatio) through 0-6 m (visible light) to radio wave legths m.

quatum umbers ad the charge Z (umber of electros, protos).

9 ultraviolet visible ifrared Characteristic spectrum of elemets Solar Spectrum ach elemet has its ow characteristic trasitios depedig o the orbit quatum umbers ad the charge Z (umber of electros, protos). These trasitios ca be aalyzed by so-called spectroscopy of light to determie the elemetal abudace!

10 Multi-lectro Atoms Z is the charge ad determies the chemical characteristics of the elemet, e.g. Z(Hydroge) Z47 (Silver). lectro trasitios ad photo emissio is more complex ad depeds o Z ad the shieldig S by ier electro shells. -trasitios to λ ( Z S ) ( Z ) ( Z ) hc γ 3.6 ( Z ) + ( Z ) 3.6 hc 3.6 hc λ

11 X-ray trasitios i high Z atoms Ag aalysis L αβγ (.9 kev) α (.6 kev) β (4.9 kev)

12 xample: Calculate the ad L x-ray lies for Ag Ag : ( Z ) 3.6[ ev ] Z 47 i 3 α β [ ev ] 583[ ev ] 9 [ ev ] 5580[ ev ] β L α L L α ( Z ) 3.6[ ev ] 4 9 ( 46) 3.6[ ev ] 3997[ ev ] i α

13 trasitio scheme with orbital mometum quatum umber Level splittig occurs due to elliptic orbitals. This itroduces fie structure i the atomic light spectrum

14 higher accuracy x-ray eergies Z lemet α α β Lα Lα Lβ Lβ 47 Ag L αβγ (.9 kev) L αβγ (.9 kev) α (.6 kev) β (4.9 kev) α (.6 kev) β (4.9 kev) asy to obtai: Typical spectra:

15 Summary For usig atomic spectroscopy methods we eed to excite the atoms of the material that should be aalyzed. The decay back to the atomic groud state cofiguratio causes the emissio of photos with characteristic eergies which ca be observed by spectroscopy methods!

Physics Methods in Art and Archaeology

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