A _ba

Einstein coefficient for spontaneous emission

a ₀

Bohr radius

B _if

Einstein coefficient between initial state and final state

e

charge on the electron

ED

electric dipole term

E _DC

Dirac Coulomb term

E _hf

hyperfine energy

E _n

eigenvalues of quantum state n

EQ

electric quadrupole term

E( t)

electric field at time t

E( ?)

electric field at frequency ?

g _a

degeneracy of ground level

g _b

degeneracy of excited level

g _N

gyromagnetic ratio of nucleus

h

Planck's constant

H _so

spin-orbit interaction hamiltonian

I

nuclear spin

I( t)

the emission intensity at time t

j

total angular momentum vector given by j = 1

l _i

orbital state

m

mass of the electron

MD

magnetic dipole term

M _N

mass of nucleus N

n _?( T)

equilibrium number of photons in a blackbody cavity radiator at angular frequency ? and temperature T

QED

quantum electrodynamics

R _nl( r)

radial wavefunction

R _?

Rydberg constant for an infinitely heavy nucleus

s

spin quantum number with the value 1/2

s _i

electronic spin

T

absolute temperature

W _ab

transition rate in absorption transition between states a and b

W _ba

transition rate in emission transition from state b to state a

Z

charge on the nucleus

fine structure constant

? ?

natural linewidth...