Giant helium molecules

Have been created by researchers at the Ecole Normale Supérieure in Paris. With atomic separations ranging from 8 to 60 nanometers, the diatomic molecules are comparable to the size of small viruses. Normally, He is chemically inert. To create the new giant molecular states, the researchers first cooled a gas of He atoms to 10 µK. Each atom was in a long-lived metastable state and carried nearly 20 eV of internal energy, more than 10¹⁰ times its average energy of motion. The physicists then used a laser to pair up He atoms through photoassociation, a process in which light-induced dipoles cause two atoms to bind to each other. To detect the molecules, the researchers recorded a temperature rise in the cloud; that increase resulted from the successful absorption of the laser light. In a typical experiment, 1% of the atoms absorb the light and form about 10^5...