PURPOSE: Show resonance radiation of iodine.

DESCRIPTION: A glass sphere containing iodine vapor is illuminated by a bright point source, and characteristic radiation can be seen as scattered light. The light scattered (absorbed and re-emitted) by the iodine vapor is desaturated yellow-green, and the light passing through the sphere is a desaturated pink, the complementary color.

SUGGESTIONS: In the photograph above, a half-silvered mirror is used to split the beam from a collimated bright point source, with half going through the sphere and half going to a screen by way of the front-surface plane mirror. The hue of the direct light can be compared with the hue of the light passing through the sphere and the hue of the light scattered by the vapor in the sphere.

Looking carefully at the path of the light beam passing through the sphere, its color is desaturated yellow-green. The entire sphere assumes a pink color, compared with the white background, because the yellow-green resonant components of the white light beam are scattered out, as seen by the yellow-green color of the light beam in the sphere.

REFERENCES: (PIRA unknown.) See Demonstration Reference File for interesting literature on this phenomenon.

EQUIPMENT: Bright point source with condensor lens, spherical flask of iodine vapor, front surface mirror, and mounted half-silvered mirror.

SETUP TIME: None.