Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Research Projects

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  • spezzano


CO+ is the cation of the second most abundant molecule in space, carbon monoxide, and it is a good tracer of Photon-Dominated Regions (PDRs). The rotational spectra of CO+, 13CO+ and C18O+ in the v = 0 and 1 vibrational states have been measured in the submillimeter-wave range. Furthermore, the first THz spectra of the main isotopic species have been measured. An isotopically invariant fit has been performed, and a set of independen molecular parameters have been derived. The measured and predicted high frequency transitions of CO+ will guide new astronomical observations. Performing high resolution spectroscopy on ions is not trivial. The ions are unstable molecules and have to be produced in situ, at cryogenic temperatures by using a DC electrical discharge. ...more


Absorption Rotational Spectroscopy
Rotational spectroscopy is a key method to investigate molecules, radicals and ions. These species are capable of motions, in particular molecular rotation. If a permanent or induced dipole moment is existent, the species is called transient and the underlying energy states are quantized and accessible for electromagnetic waves. The energy distances between the rotational levels are such, that mostly the transition lines are in the cm- (up to 30 GHz), mm- (up to 300 GHz) and in part shorter wavelength ranges of the electromagnetic spectrum. Since the energies necessary to excite the rotational states are low, the typical temperatures in the ISM are sufficiently high for exiting these states (T = 5 K to much more than 100 K). The line frequencies of the transitions can be measured with great accuracy; this, in turn, gives precise molecular parameters, which allows calculating reliable predictions of new molecular lines which helps to identify new molecular species in space. Such line lists and the parameters of many species are available in our Cologne Database for Molecular Spectroscopy (
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Recent Results

For the production of CO+ a cryogenic discharge cell was used, modified with a long hollow cathode to optimize the production of positive ions. Typically 80 mA discharge current was used, through pure CO at a pressure of about 0.3 mbar. Accurate THz measurements have been performed on CO+, leading to a more accurate fit and improved predictions at high frequencies: for example the previously predicted value for the NJ = 1021/2 - 1123/2 line at 1.29 THz in the CDMS catalog was off by 1.5 MHz from the observed value, while with the improved predictions, this transition instead has a calculated uncertainty of only 560 kHz at 2.5 THz.
Spectra of the lines of CO+ measured for this work. The lines shown are the average of forty scans, with a total integration time of about thirty minutes.



  • Silvia Spezzano was supported by the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics
  • Funding by SFB 956..