Sodium Energy Levels

Sodium
spectrum

Why
do levels vary with orbital quantum
number?

Electron
energy level diagrams

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Sodium Spectrum

The sodium spectrum is dominated by the bright doublet known as the
Sodium D-lines at 588.9950 and 589.5924 nanometers. From the energy
level diagram it can be seen that these lines are emitted in a
transition from the 3p to the 3s levels. The line at 589.0 has twice the
intensity of the line at 589.6 nm. Taking the range from 400-700nm as the
nominal visible range, the strongest visible line other than the D-lines
is the line at 568.8205 which has an intensity about 0.7% of that of the
strongest line. All other lines are a factor of two or more fainter than
that one, so for most practical purposes, all the light from luminous
sodium comes from the D-lines.

The illustration at left shows the interference pattern formed
by the sodium doublet in a Fabry-Perot
interferometer. At right is a sketch of the origin of the sodium
doublet.

Sodium
light from an electric pickle!

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The Electric Pickle

A far-fetched example of a non-ohmic resistor is the electric pickle. A
considerable amount of light can be obtained by connecting ordinary
household 120 volt AC voltage across a pickle. After the pickling process,
there are Na+ and Cl- ions present. The standard explanation is that the
electric current excites the sodium ions, producing light similar to that
of a sodium
lamp.

Thanks to Brian Lucy for this example.

Currents in ionic solutions are often not linearly proportional
to the applied voltage. When Ohm's
law is used with ordinary carbon resistors, the ratio of voltage
to current is constant, but the variation in light output suggests
that this is not the case with the electric pickle.

Warning!
The electric pickle is a serious shock hazard!

From the color, I had presumed that the light from the pickle was
at least partly sodium light from the sodium chloride used in the
pickling process. But I had no idea that it was such pure sodium
light! The spectrum of the electric pickle at right was taken by
Benoit Minster of Grenoble, France using a Lhires II spectrograph
and a digital camera. It's as pure a sodium doublet spectrum as I
get using a sodium lamp! If it weren't for the electric shock hazard
posed by the electric pickle, we might suggest them as low-cost
sodium light sources!

Electric
pickle movie

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Sodium Energy Levels:Orbital Dependence

The sodium 3s level is significantly lower than the 3p
because of greater penetration past the shielding of the 1s
electron.

Both
levels penetrate enough to be significantly lower than the n=3
hydrogen energy which they would have if the shielding were perfect.

Why
do levels vary with orbital quantum number?

Sodium
doublet

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