Hydrogen bonding plays an important role in determining physical and chemical
properties of many organic substances such as peptides or sugars. The specific
behaviour of hydrogen bonds under the condition of an intensive electronic
excitation, as given by the impact of a fast heavy ion or by UV-laser
irradiation, will be discussed. There is some evidence for a mechanism which
breaks hydrogen bonds selectively, promotes proton transfer reactions and thus
enables the  desorption of intact molecular ions.