Study of Fragmentation Patterns by Beam Modulation Mass Spectrometry

Abstract

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.

Reactions of borane (BH3). V. Mass spectrometric observation of the products of addition to diborane(L) and pentaborane(9)

“…Phase Spectra.-So that the identity of the products observed could be more firmly established the average molecular weights of the neutral progenitors of the m/e 38 ions produced in the reaction of BHS with B2H6 and of the m/e 71 ions produced in the reaction of BHS with B5H9 were measured by utilizing the fact that the phase shift between the reference signal and the ion signal is related to the average flight time in the molecular beam. 12 The results of these measurements are shown in Figures 3 and 4. For the reaction of BH3 with B2He the relative phase of the m/e 38 ion peak was measured with respect to m/e 38 from aliene (Figure 3) and m/e 58 from butane and m/e 27 from diborane (not shown).…”

High Temperature Chemistry: Stabilities and Structures of High Temperature Species

“…For example, ionization cross sections for molecular species are still mainly estimated from the Otvos-Stevenson rule, although a number of relative cross-section data are becoming available. The use of a velocity selector-mass spectrometer system (33) and the technique of partial and total vaporization isotherms (34,35) have allowed a significant advance in the knowledge of molecular ioniza tion cross sections. Considerable progress in obtaining ato mic cross-section data has also been made (36,37).…”