MOSCOW, April 13. /TASS/ Physicists from Siberian Federal University (SFU) together with their colleagues from Royal Institute of Technology in Stockholm, Sweden, have demonstrated that "heavy water" changes its properties while exposed to X-ray irradiation. The study’s results have recently been published in the journal Scientific Reports and might serve as a clue for understanding the mechanisms of controlling chemical reactions by means of irradiation.

The study’s authors have revealed that the localization of vibration is breached once molecules are exposed to X-rays, the SFU’s press office reported.

What are localized vibrations?

"In the water molecule, H2O, both hydrogen atoms vibrate simultaneously," Swedish Professor Faris Gelmukhanov, a co-author of the study commented. "They might oscillate in a symmetric way, going in a synchronized manner away from, or towards the central oxygen atom. Alternatively, they can perform an antisymmetric motion going in one direction. But anyway, the vibrational motions of both hydrogen atoms are correlated. Such vibrations are dubbed "delocalized."

This picture is completely changed if one of the hydrogen atoms is replaced with the deuterium (D) which is twice as heavy as hydrogen. In such an asymmetric molecule HOD, the atomic vibrations become localized implying that the light hydrogen atom and heavy deuterium atom are oscillating near the central oxygen in an independent way and with different frequencies.

What happens with the "heavy water" molecule under X-ray irradiation?

The independent oscillation character changes under X-ray irradiation. Such an impact transfers the heavy molecule HOD in an excited state where the hydrogen and deuterium are again oscillating in sync as in the regular water molecule.

"The light hydrogen atom moves faster than heavy deuterium atom and this is exactly the asymmetry in kinetic energy which is responsible for the asynchronous behavior of vibrations in non-excited stated of heavy water," Professor Gelmukhanov commented. "However, from the viewpoint of electrostatics, the atoms H and D are absolutely equivalent since they have the same charges."

The quantum calculation of scientists has revealed that in the molecule excited with the X-ray irradiation, the second factor ("symmetric electrostatics") outperforms the first one ("asymmetric kinetic energy") which is the reason for the correlated motion of H and D in an excited state.

The scientists believe that the disclosed "co-existence" of delocalized and localized vibrations in molecules is of primary importance for further studies of migrations of vibrational excitations in solid and liquid materials. The study’s results will assist in researching the processes of energy transfer in condensed media and in the development of controlling mechanisms of photostimulated chemical reactions.