For the first time, a research group consisting of Tokyo Metropolitan University, RIKEN, and Gothenburg University observed a luminescence phenomenon called "retrofluorescence" that occurs in isolated molecules in a vacuum such as outer space.
When a molecule absorbs light, the internal electrons have high energy (electron excited state).When this electron returns to a low energy state (electron ground state), it emits extra energy as light (fluorescence).However, in many cases, the energy of the excited electrons is instantly converted (internal conversion) into the vibrational energy of the molecule, and the energy continues to move to the surrounding substances and does not emit light.
On the other hand, if the surroundings of the molecule are in a vacuum state such as outer space, the vibration energy generated by internal conversion cannot move to the surrounding substances and accumulates in the molecule.At this time, the vibration energy is converted into electron energy (reverse internal conversion), and when the energy returns to a low state, light (retrofluorescence) is emitted.The existence of this retrofluorescence has been predicted for more than 30 years, but it is difficult to create an isolated environment for molecules, and no phenomenon that can be confirmed as retrofluorescence has been found.
Previous studies have speculated that negative ion molecules with six linearly bonded carbon atoms emit retrofluorescence.This time, the research group used a device called an "electrostatic ion storage ring" to confine several types of molecular negative ions up to 6 carbon atoms, and observed the luminescence emitted from the ions with a highly sensitive photodetector.As a result, we succeeded in detecting retrofluorescence only from ions with 6 carbon atoms.
It is thought that retrofluorescence occurs in many molecules, and it is expected that the details of its properties will be clarified in the future and the energy exchange seen in molecules and electrons will be elucidated.In addition, it is expected that new interstellar molecules will be discovered by investigating visible light in outer space.
