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Physicists from the University of Innsbruck are looking for molecules containing nitrogen in the space. Using terahertz spectroscopy, they directly measured two spectral lines for a particular molecule for the first time. The frequencies found are characteristic of the amide ion, a negatively charged nitrogen molecule. With spectral lines now determined, researchers can search this species in space.
In 2014, astrophysicists discovered a spectral line in the Herschel space telescope observation data and provisionally assigned it to the amide ion. This would have been the first evidence of the existence of this molecule in space. The physicists of the group of Roland Wester of the Institute of Physics of Ions and Applied Physics of the University of Innsbruck have now shown that this assumption was incorrect.
Characteristic Frequencies
In addition to stars, galaxies are populated with regions containing gigantic dust and gas clouds. These regions, constituting the interstellar medium (ISM), are the birthplace of new stars that form when clouds collapse under their own gravity and reach sufficient densities for fusion reactions to occur. In order to better understand these processes, it is important to know exactly the chemical composition of the ISM which is most often determined by the frequencies (spectral lines) measured by radio telescopes.
In the case of the amide ion, the team led by Roland Wester measured for the first time two previously unknown frequencies in the laboratory. The method adopted, known as terahertz spectroscopy, made it possible to determine the lines a hundred times more precisely than what was previously possible. "In this technique, the wavelengths between microwaves and infrared light are used," explains the physicist. "This makes it possible to study the rotation of very small molecules. For larger molecules, we can determine the vibrations of whole molecular groups."
In a project funded by the European Research Council ERC, Roland Wester's group developed a method by which molecules confined in ion traps are excited by terahertz radiation. "The amide ion is made up of one nitrogen atom and two hydrogen atoms, it looks like water and behaves very well in terms of quantum mechanics", explains Olga Lakhmanskaya of Roland Wester's team. "For the first time, we directly measured the elemental excitation of the rotation of this molecule." The evidence also came through close collaboration with the theoretician Viatcheslav Kokoulin of the University of Central Florida, who was a visiting professor at the University of Innsbruck for a semester
Provisional Assignment Refuted
The physicists of Innsbruck have now been shown that the previously measured spectral line can not be produced by amide ions in comparison with the data obtained from the Herschel space telescope. "We were able to show, with our measurements, that this temporary assignment is not correct," says Roland Wester. In the Universe one can find various nitrogen molecules like ammonia but, according to the Innsbruck experiments, it remains to demonstrate that the amide ion is also present. The second spectral line determined by physicists could, however, help in the search for this species in space. "We hope that in the future, with new telescopes, this line can be observed leading to its detection in the space." The Wester team now wants to apply the new method to molecules with four or five atoms, where vibrations and rotations are much more complex than with the triatomic amide.
Learn more:
Planetary nebula lasers
More information:
Olga Lakhmanskaya et al., Rotational Spectroscopy of a Triatomic Molecular Anion, Physical Review Letters (2018). DOI: 10.1103 / PhysRevLett.120.253003
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