Thursday, March 08, 2012

What does a molecule look like?


The headline is wrong . This is not "real time;" they are looking at diffraction patterns which are by nature statistical.

What they are probing is what an average N2 molecule looks like at a particular time relative to the impulse of an ultra-short laser pulse. The laser pulse ionizes the molecule and then, under the influence of the electric field of the laser pulse, the electron returns and scatters off the ion.

They measure the distribution of the scattered electrons in both position and energy, and from that reconstruct the shape and momentum of the thing they scattered off.

In addition, the time at which the electric field of the laser pulse pulls the electron back towards the ion will vary depending on the wavelength of the laser light, so by varying the wavelength they can bounce the electron off the ion at slightly different times. This can give them an image of what the ion looks like at different times.

4 comments:

Texan99 said...

Whatever it is that electrons are doing when they "move," or have angular momentum, makes my head hurt. The only movement I understand is things that start here, and move continuously from here to over there. Electrons seem to appear here and there according to somewhat-predictable rules, but it's as if they were rotating in and out of our reality and spent the intervening journey somewhere else.

james said...

Or that they're a little bit everywhere at once, but mostly "over there."

Texan99 said...

Yes, I understand that one way to think of particles is that they take all paths, but we "see" the path that's the most likely, or that the most likely path somehow resonates with the ones most like it, thus enforcing it and making it perceptible. I got this from Feynman's "Q.E.D.," a book I've read more than once trying to make sense of the intuitive concepts without possessing the math I'd apparently need for a deeper understanding. That all-paths business bends my mind.

I don't understand people who find the material world aimless or chaotic. For me, the amazing thing is how orderly and clever it is, how it reveals startling but faithfully predictable patterns or mechanisms you'd never have dreamed up on your own, and how astonishing it is that we should be able to perceive them.

james said...

Someone said that the most amazing thing about the world was that it was understandable.