The Humble Hydrogen Atom
Back in May 2013, scientists announced that they had managed to capture a photo of an electron’s whizzing orbit within a hydrogen atom, using a unique new technology of ‘quantum’ microscopy. Ladies and gentlemen, let’s take a short trip into the infinitesimally small! Here is the first photograph of a hydrogen atom!
According to NASA’s Astrophysics Dictionary, atomic hydrogen H (“monatomic” hydrogen) constitutes about 75% of the elemental mass of the Universe. (Although it is worth noting that most of the Universe’s mass is not actually in the form of chemical elements, or “baryonic” matter. Food for thought, and another story to be told!)
On Earth, it is extremely rare to come across isolated hydrogen atoms outside experimental settings. Hydrogen usually combines with other atoms into compounds, or with itself to form ordinary (diatomic) hydrogen gas, H2.
The hydrogen atom H contains a single positively charged proton p and a single negatively charged electron e, bound to the nucleus by the Coulomb force. It is electrically neutral. The hydrogen atom is unique because it has only one electron.
And the diameter of a hydrogen atom is no bigger than about twice…
The Trouble with Mighty Small Things
Observing the tiniest building blocks of matter has always been tricky. Not merely because of the infinitesimal size of an atom…
You see, mighty small things operate in mighty strange ways! At the atomic scale, Nature’s behaviour seems so absurd that particles interactions can only be explained by a special branch of physics. Electrons have neither definite orbits, nor sharply defined ranges. Instead, their positions must be described by probability distributions that taper off gradually as one moves away from the region of the nucleus, without any sharp cut-off.
Mighty small things operate in mighty strange ways!
The development of Quantum Mechanics in the early part of the 20th century has had a profound influence on the way that scientists now understand the world. At the centre of it, is the concept of a wave function that satisfies the time-dependent Schrödinger equation.
Here we encounter another very real difficulty. Things get even weirder. The basic act of observing such infinitesimal particles seems to be affecting their very existence!
Getting around such a reality-bending concept as the Uncertainty Principle, scientists have relied upon quantum theory to define the behaviour of particles in time and space, with complex equations that predict the probabilities of finding electrons, at any particular moment OR in any particular locations of their orbit around an atom’s densely packed nucleus.
The Schrödinger equation governs the atomic structure, describing it as a wave function. But so far, the actual observation of that structure has seemed to inevitably destroy it…
The new “quantum microscope” invented by Aneta Stodolna and her colleagues at the FOM Institute for Atomic and Molecular Physics (AMOLF) in the Netherlands, uses the process of photoionization and an electrostatic magnifying lens to observe directly the electron orbital paths of an excited hydrogen atom.
A New Look at the Hydrogen Atom Wave Function
As described in the journal Physical Review Letters, Stodolna et al. 2013’s experiment imaged the wave function of a hydrogen atom. Hydrogen is uniquely suited for the new photography technique because the first element in the periodic chart contains just a single electron.
Initially proposed over 30 years ago, the experiment provides a unique look at one of the few atomic systems that has an analytical solution to the Schrödinger equation.
Stodolna and her team first fired two lasers at hydrogen atoms inside a special chamber, thus ejecting electrons from the atoms at speeds and directions dependent on their underlying wave functions. A strong electric field inside the chamber guided the electrons through a lens and onto a detector, which displayed the electron distribution as light and dark rings on a phosphorescent screen.
The phase difference between the trajectories leads to an interference pattern, which Stodolna et al. 2013 magnified with an electrostatic lens and managed to capture.
This interference pattern was photographed using a high-resolution digital camera. This is the first ever such photo taken.