A novel method is presented here to determine accurately the conversion efficiency in low energy collision processes. Using blackbody infrared radiation, the initial thermal energy of a selected molecular ion is both well defined and well known. Collisional activation is subsequently used to probe the additional energy needed to reach a particular final internal energy distribution, characterized by a given fragmentation rate (e.g. 50% of the molecular ion being decomposed). The method is discussed for collision induced dissociation under multiple collision conditions using resonant excitation in a Fourier transform ion cyclotron resonance ion trap. By variation of the thermal energy content the collisional energy necessary to obtain 50% fragmentation rate is also changed. Knowing this change, the collisional to internal energy transfer can accurately be determined. In the case of Leucine-Enkephaline using Ar collision gas it was shown that 4.4% of the laboratory frame collision energy is converted into internal energy in the resonant excitation collision cascade. In individual collisions 9.6% of the centre of mass collision energy is converted into internal energy. Note, that this value is accurately determined as an average for collisions in the 4-6 eV centre of mass collision energy range, but is approximately the same in the 0-4 eV range as well.

Jan 1st 1998

bio-imaging-ms