The document discusses alkali metals, spin-orbit interaction, and the fine structure of alkali spectra. It first describes alkali metals as a group of reactive soft metals including lithium, sodium, potassium, rubidium, cesium, and francium. It then explains that spin-orbit interaction causes shifts in electron energy levels due to the interaction between an electron's spin and the magnetic field from its orbit around the nucleus. Finally, it discusses how spin-orbit coupling splits energy levels into substates, resulting in multiplets in spectra known as fine structure, with the splitting determined by the quantum numbers j, l, and s.

1. ASSIGNMENT ON
• SPECTRA OF ALKLI ELEMENT, SPIN ORBIT
INTERACTION & FINE STRUCTER OF ALKLI
SPECTRA

2. SPECTRA OF ALKLI ELEMENT
ALKLI METALS
SPIN ORBIT
INTARACTION
FINE STRUCTUR

3. ALKALI METAL
• The alkali metals are a group (column) in
the periodic table consisting of the chemical
elements lithium (Li), sodium (Na),
potassium (K), rubidium (Rb), caesium (Cs) and
francium (Fr)
• The alkali metals have very similar properties: they
are all shiny, soft, highly reactive metals at standard
temperature and pressure
• All the alkali metals react with water, with the
heavier alkali metals reacting more vigorously than
the lighter ones.

4. SPIN ORBIT INTERACTION
THE spin–orbit interaction (also called spin–
orbit effect or spin–orbit coupling) is an
interaction of a particle's spin with its motion.
The first and best known example of this is that
spin–orbit interaction causes shifts in
an electron's atomic energy levels due to
electromagnetic interaction between the electron's
spin and the magnetic field generated by the
electron's orbit around the nucleus.

5. Spectra of alkali atom

6. Spin-orbit coupling (I)
• An electron revolving about a nucleus finds
itself in a magnetic field produced by the
nucleus which is circling about it in its own
frame of reference.
• This magnetic field then acts upon the
electron’s own spin magnetic moment to
produce substates in terms of energy.
S=1/2 could make some single state (n,l,m)
split into two substates.

7. Spin-orbit coupling (II)
• The coupling of two magnetic moments in an
atom leads to an addition of the two angular
momenta to yield a total angular momentum.
j=l+s
• The total angular momentum has the magnitude
of with j=|l±1/2| for a single electron system.
The quantum number j is the quantum number of
the total angular momentum .
• For a p electron, l=1, s=1/2, there are two states
with j=1/2, 3/2, respectively.

8. Fine structure
• All energy levels except the s states of one-
electron atoms are spit into two substates.
This produces a doublet or multiplet
structure of the spectral lines, namely, fine
structure.
• It can not be explained by Coulomb
interaction between the nucleus and the
electrons. It results from a magnetic
interaction between the orbital magnetic
moment and spin magnetic moment of the
electron, called spin-orbit coupling.

10. Made By:
Anita Malviya