Statoary states of atos ad olecules
I followg wees the geeral aspects of the eergy level structure of atos ad olecules that are essetal for the terpretato ad the aalyss of spectral postos the rotatoal vbratoal ad electroc spectra of olecules wll be revewed. Spectroscopc easureets provde foratos o the saple uder study ecoded the for of le postos le testes ad le shapes. The le postos ca be used to extract forato o the eergy level structure of atos ad olecules. Le testes ad shapes provde characterstcs of the stregth of teracto as well as dyacal forato o tra- or exteral teractos of olecules.
Geeral coets o soluto of Schrödger equato te depedat Schödger equato separablty of the Schrödger equato separato of the ceter of ass ear separablty sutable coordates systes approxato techques
Descrpto of atoc or olecular states z x y z x N y N z N y For a syste of N partcles wth coordates qx y z wth...n the te depedat Schrödger equato s x x y z... x N yn zn x y z... x N N N y z -are the egefuctos of -ther eerges - represets a label a quatu uber or a set of quatu ubers for the state I x...z N I dx...dz N s the probablty that state partcle s located betwee x y z ad x dx y dy z dz partcle betwee x y z ad x dx y dy z 3 dz 3...
... x z y x z y x q x p z y x p p p p h h... q p z y x z y x V p V T N N N N T ad V are operators of etc ad potetal eergy Soluto of the Schrödger equato for ay partcles proble s coplex ad geerally posble to obta explctly. Oe has to carefully set altoa of the syste: -separato of the ceter of ass oto -represetato the ost approprate coordate syste e.g. syetry of the force feld -separablty of the altoa o a su of operators that ca act o dstct sets of varables -cosder separato o doat ad perturbg altoa copoets ad use of aproxato ethods e.g. perturbato ad varatoal ethods
Atos datoc ad polyatoc olecules Atos: ucleus e - hydroge hydrogec atos or os ucleus N e - Molecules: ucle electros N ucle electros Coplexes ad clusters: coplex force feld Very large systes - atos: bul propertes---sold state physcs
erarchy of otos ad eerges atos ad olecules Atos ad olecules: oble ucleus ad fast ovg electros The dfferet types of oto olecule electroc vbratoal rotatoal taes place o dfferet te scales ad are assocated wth dfferet cotrbutos to the total eergy. Ths herarchy of te scales ples the approxate separablty of the correspodg otos that les behd the so-called Bor-Oppeheer approxato
Syetry A olecule possesses structural syetry ad t ca be descrbed ters of rotato axes ad reflecto plaes Use of the group theory ad cocept of syetry helps to uderstad olecules ad ther spectra.
Separablty- exaples
Separato of the ceter of ass oto I atos ad olecules free space the oto of the ceter of ass s exactly separable fro the teral oto because the potetal Vq oly depeds o the dstace r j betwee the ucle ad electros: Q c P c qt pt Coordates ad oetu operators of the ceter of ass oto ad these operators the ceter of ass coordates c The overal traslatoal oto of the ato/olecule ca be treated as that of free partcle of as M a free space or f the exteral potetals are preset accordg to the potetal eergy fucto. I spectroscopy oe studes the trastos betwee the eergy levels assocated wth the teral oto of atos ad olecules ad cocetrates o a proble of reduced desoalty 3N-3 It dffers fro the altoa c that the etc eergy ter cotas the reduced ass μ stead of for stace the free-electro ass e.
Separablty of altoa e.g. depedat coordates
Near separablty
Perturbato theory: revew It s cocer wth fdg the chages the dscrete eergy levels ad egefuctos of a syte whe a sall dsturbace s apped Sall suggests that oe ca expad the perturbed egefuctos ad egevalue as power seres. Ths s ost coetly accoplshed ters of a paraeter l such that the zero frst etc powers of l correspod to the zero frst...orders of perturbato calculatos λ λ λ... λ λ...
......... λ λ λ λ λ λ λ... 3 3 By equatg the coeffcets of equal powers λ o both sdes to obta seres of equatos represetg hgher orders of perturbato s ay of uperturbed egefuctos ad s ay of uperturbed egevalues *
Frst order perturbato s because a a a The wave fucto s calculated by expadg t ters of the : Substtuto t to the secod equato * gves: a The forer equato gves as the expectato value of for uperturbed state. > s s s s The calculatos of to a gve order requres owledge of oly to the ext lower order.
Secod-order perturbato I I a a a
ergy ad wave fuctos to the secod order I I ] [
Geeral coets:. Ay of the fuctos s ca have a arbtrary ultple of added to t wthout affectg the value of the left sde ad hece wthout otherwse affectg the deterato of s ters of lower-order fuctos. s s> * s dτ. Ier product of fo ad the left sde of each of solutos s zero ad oe ca develop followg equato: s s s s >