Wavelength High Temp

Using interstellar CN to study the cosmic background radiation. (a) We see what observations are done.The cloud with the CN is in between the Earth and a bright star.We take a spectrum of the star and see absorption lines from the CN. (b) We see how the strength of the absorption lines changes as we increase the temperature of the background radiation. In the upper left we see the energy levels. Electrons jumping from one level to another give us the big change in energy. Much smaller changes occur when the rate of rotation of the molecule changes. (These rotational energy shifts are exaggerated in the diagram.) Transitions 1 and 2 both correspond to the same jump by the electron, but they occur with the molecule in slightly different rotational states. In the upper right, we see the populations of the levels at low and high temperatures.The thicker the black line, the more populated the level.The red arrows indicate how strong the absorption is.The thicker the line, the stronger the absorption. In the lower panels, the resulting low and high temperature spectra are shown.

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