Schematic diagram of the experimental setup. The prepared sample is placed in front of our TOF-MS and is irradiated by the pump laser that strikes the surface via openings in the extractor front and the repeller lenses. Neutral fragments ejected from the surface travel a distance of 29.4 mm into the ionization region of the mass spectrometer where they are ionized by the probe laser after a fixed time delay. The ionized parent (and fragment) ions are focused onto specific locations on the detector based upon their initial trajectory. Images of the phosphor are recorded by the PImMS camera that records both mass spectrometric data and images simultaneously.
Three-dimensional rendering of our imaging TOF-MS showing the imaging lenses as well as part of the flight tube. The TOF-MS has been sliced in the horizontal plane to better illustrate the geometry of the instrument.
Time-of-flight mass spectra taken for both (a) slow and (b) fast channels. Below each mass spectrum is the data in its 3D form where the horizontal axis represents time and the vertical axis represents the detector plane with units of pixels. The 3D images have been rotated slightly about the time axis to better illustrate the ion clouds. Thus, the vertical axes do not correspond to single detector axis (i.e., x or y) but rather some arbitrary combination of the two.
Horizontal cross sections taken for images of masses 29–27 (left to right) at (a) 59 μs laser delay and (b) 24.6 μs laser delay. For data taken at the longer delay, the degree of fragmentation for ethyl radical is quite severe and there is signal which falls outside of the limits imposed by our detector function. Fragmentation does not appear to be as severe for data taken at the shorter delay, although there is a clear broadening of the distribution for masses 28 and 27.
Angular distributions of ethyl radical desorption for the (a) slow and (b) fast channels along with cosn(θ) fits to the data. For the slow channel n = 39.5 and for the fast channel n = 39.0. The angular distribution of ethyl radicals is essentially the same for both kinetic energies studied in this work.
Article metrics loading...
Full text loading...