Shake-up studies of model systems for adsorbates are presented. The molecule CO adsorbed on transition metal surfaces belong to one of the most studied systems in surface science. The interest is motivated by fundamental questions about the adsorbate-substrate interaction as well as technical applications, such as catalysis. A good starting point in order to get more detailed understanding of the CO-metal interaction is to study the transition metal carbonyls, where CO is coordinated to metal atoms. It has been found that many aspects of the adsorbate systems can be modelled by these molecules. These are the main reasons for studying the molecules Mo(CO)6 and Cr(CO)6, for which results are reported in this thesis.