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Scientists track ultrafast changes in molecules via tunneling ionization

June 07, 20:13 UTC+3 MOSCOW
This finding will open access to control chemical reaction paths
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MOSCOW, June 7. /TASS/. Russian scientists together with colleagues from Japan and China have observed the structural molecular changes that take place within billionths of a billionth of a second, the press service of the Moscow Institute of Physics and Technology (MIPT) said on Tuesday.

The results of experiments coincide with theoretical predictions, implying that the suggested method could be applied to visualize and control molecular configurations on a real time basis.

This finding will open access to control chemical reaction paths.


"Attophysics is currently a very ‘fundamental science’, but we could suggest a range of possible applications. Knowing the shell configuration changes or the nuclei motions in course of a chemical reaction, we could ‘shoot’ with a laser in the right place at the right time to produce a controlled outcome of a chemical reaction," said Oleg Tolstikhin, chief researcher and associate professor of MIPT’s Theoretical Physics Chair and head of the Attosecond Physics group.

Tolstikhin and his colleagues work in the field of attophysics - a science dealing with extremely fast processes. Exemplarily, the reconstruction of electron shells or the displacements of atomic nuclei in molecules during chemical reactions are considered. The main objective is to achieve tracking the changes in the molecular structure with attosecond time resolution. i.e. billionths of a billionth of a second.

One attosecond is a time interval of a quintillionth of a second. To note as a comparison that the ratio between an attosecond and a second can be approximately given as a ratio between a second and 31.71 billions years.

The results approved the theory

The scientists irradiate nitric oxide (NO) molecules with short femtosecond pulses exciting an outer electron to a higher state. Then the excited electron returns and scatters on the molecule resulting in the ionization, i.e. the dissociation of a molecule into a positive nitrogen ion and an oxygen atom. 

With the measured momentum distribution of nitrogen ions in the ground and excited initial states the scientists have managed to track the dependence of the rate of tunneling ionization on the laser parameters. The results of the experiment are in the fairly good agreement with the predictions of the asymptotic ionization theory.

The scientists have also developed a new technique of unraveling ionic structure by means of photoelectron holography. After irradiation of an atom with short femtosecond pulses, the excited electron flow appears similarly to the experiments with nitrogen monoxide. The electron scatters on the ion, so by tracking the scattering process, the structure of ion could be decoded.

"In our study, to simplify the calculations, we consider a model atom with one electron. But the principle of restoring the ion structure by the scattering pattern should be applicable to all atoms and molecules," Tolstikhin said.

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