March 12, 2010

Blue Ice
At the first of several large snowstorms this past winter, Warren Wilson's Tom LaMuraglia operated the snowplow (front loader) to clear the roads around campus.  Thank you, Tom!

In several of the many large snow piles left by the snow clearing machine, neighbor Tom Showalter  noticed the definite blue color deep within the cavities of the snowbank.  This coloration of snow is a real effect - not just an illusion or faulty color balance setting of the camera.

As light travels through snow, ice, or pure water, the light from the red end of the visible spectrum is partially absorbed.  If red is removed from white light, the remaining light appears cyan or "bluish".  The greater the distance the light travels in the H₂0 material, the greater the reduction of the red colors.  Thus the blue tint is more pronounced deep within the cavity in the snow bank.

The physical chemical reason for this light absorption lies in the vibrations of the oxygen-hydrogen bond in the water molecules.  The oxygen-hydrogen bond will vibrate at a frequency corresponding to infrared wavelength.  However, the bond stretch in most molecules is "non-linear", i. e. stretching more than twice as much does not require twice the stretching force.  As a result the bond not only absorbs light at the natural vibrational frequency of the bond, it also absorbs light at overtones of the fundamental.  These vibrational overtones occur in the visible red - a higher frequency than the infrared fundamental.  If water is made by replacing the hydrogen in H₂0 with deuterium, D₂0, the larger mass makes for a smaller vibration frequency, hence the absorption of the light for D₂0, occurs further in the infrared.  As a result D₂0 does not show the blue coloration.  (Charles L. Braun and Sergei N. Smirnov, J. Chem. Edu., 1993, 70(8), 612, summarized at the web site:http://www.dartmouth.edu/~etrnsfer/water.htm).

Due to Spring Break at Warren Wilson College, there will be no Physics Photo of the Week next week (March 19).  The next Physics Photo of the Week will be published on March 26, 2010.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to dcollins@warren-wilson.edu. 

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.


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