Final Report Summary - ELECSPECIONS (Electronic spectra of cold, large interstellar ions)
In this ERC project, ElecSpecIons No. 246998, the goal was to develop a general method to measure the electronic spectra of large molecular ions at temperatures comparable to the interstellar medium, -250 to -270 °C. These conditions are achieved by using a helium refrigeration system. Cations are confined within a trap using inhomogeneous electric fields to hold positive species, axially and radially, in a specified volume. As a collision gas, helium is beneficial such that it does not condense on surfaces at these low temperatures. Helium attains the -250 to -270 °C of the refrigeration unit, and through three-body collisions with helium, molecular ions are cooled down to a similar temperature and complex with one or more helium atoms.
After cations are sufficiently cooled with helium atoms as a collision partner, the positive ions interact with laser radiation. The electronic spectra are recorded by observing a change in intensity of a particular mass-to-charge ratio as a function of laser wavelength. For a comparison of laboratory and astronomical data, molecular ions have to be probed at low temperatures to obtain high-quality electronic spectra of these species of interest.
One of the major achievements of this project was the development of a new general method to obtain the electronic spectra of molecular ions. This technique is based the condensation of helium onto cations through three-body collisions with these rare gas atoms. This approach is called laser induced inhibition of complex growth, being demonstrated by measuring an electronic transition of N2+. This method has also been used to obtain rotational and vibrational spectra of other molecular ions by other groups.
Another achievement has been the identification of buckminsterfullerene cation, C60+, as the carrier of two astronomical absorptions at 957.7 and 963.2 nm. This result will have future implications in astrophysics, especially on the formation and stability of such ions in the harsh environment of outer space.
Other electronic spectra of molecular ions of astrophysical relevance have been recorded and compared to astronomical absorptions. One such class of cations, protonated polyaromatic hydrocarbons (H+PAHs), were proposed to be candidates of the diffuse interstellar bands. However, from our measurements of the electronic spectrum of protonated pyrene and coronene, we have shown that these positive species containing up to 37 atoms are not present in the interstellar medium.
After cations are sufficiently cooled with helium atoms as a collision partner, the positive ions interact with laser radiation. The electronic spectra are recorded by observing a change in intensity of a particular mass-to-charge ratio as a function of laser wavelength. For a comparison of laboratory and astronomical data, molecular ions have to be probed at low temperatures to obtain high-quality electronic spectra of these species of interest.
One of the major achievements of this project was the development of a new general method to obtain the electronic spectra of molecular ions. This technique is based the condensation of helium onto cations through three-body collisions with these rare gas atoms. This approach is called laser induced inhibition of complex growth, being demonstrated by measuring an electronic transition of N2+. This method has also been used to obtain rotational and vibrational spectra of other molecular ions by other groups.
Another achievement has been the identification of buckminsterfullerene cation, C60+, as the carrier of two astronomical absorptions at 957.7 and 963.2 nm. This result will have future implications in astrophysics, especially on the formation and stability of such ions in the harsh environment of outer space.
Other electronic spectra of molecular ions of astrophysical relevance have been recorded and compared to astronomical absorptions. One such class of cations, protonated polyaromatic hydrocarbons (H+PAHs), were proposed to be candidates of the diffuse interstellar bands. However, from our measurements of the electronic spectrum of protonated pyrene and coronene, we have shown that these positive species containing up to 37 atoms are not present in the interstellar medium.