Multiphoton ionization mass spectroscopy of acetaldehyde

Abstract

Details of the positive ion fragmentation patterns of acetaldehyde produced by collisionless multiphoton ionization are presented. Fragments are generated in the ion collection region of a quadrupole mass spectrometer and analyzed with unit mass resolution. Daughter ions are found corresponding to the absorption of up to five photons. All fragment ions show the same excitation spectrum, which closely resembles that obtained with total ion collection in both the mass spectrometer and a conventional parallel plate ionization cell. Individual fragment ion production depends strongly on laser power, going approximately as Ip, where p=1.17±0.07 for CH3CHO+, up to p=3.54±0.09 for CH+3. Total ion production varies as p=2.19±0.08. Considerable deviation from a simple power law dependence can be found for some fragments, however. A rate equation approach is used to explain the experimental results.