Study of Fragmentation Patterns by Beam Modulation Mass Spectrometry

A new mass spectrometric technique is described by which information can be obtained on the specific progenitor or progenitors of a mass peak. The method comprises modulating the neutral beam at an appropriate frequency and observing the ion signal with a phase‐sensitive detector. Measurement of signal intensity at different phase angles with respect to a point of origin provides a curve from which can be extracted information on the relative contribution of different species in the neutral beam to the ion signal. A theoretical analysis of the method is described, and theoretically calculated intensity vs phase angle curves are presented for some systems of interest. Curves for AlF are compared with experimental data and very good agreement demonstrated. Preliminary data on the pressure ratios of monomer, dimer, and trimer in LiF vapor are discussed.