Photoionization ion cylotron resonance spectroscopy: a study of three C_3H_6O isomers

Abstract

Photoionization ion cyclotron resonance (pi-icr) spectroscopy is described in detail. The construction and use of rare gas resonance line lamps employing LiF windows is described, with principle emphasis on the argon resonance line lamp that produces photons of 11.62 and 11.83 eV. Calculations of the number density and single resonance signal intensity are made for primary, secondary, and tertiary ions, and the low pressure lineshape calculated for an unreactive primary ion. The ion chemistry of propanal, acetone, and propylene oxide (empirical formula C_3H_6O) is investigated using pi-icr with the argon resonance line lamp. The major reaction sequence in propanal and acetone is parent ion producing protonated parent ion, which condenses with the parent neutral to produce the proton bound dimer. This is also the reaction sequence in ethylene oxide. In propylene oxide, however, the parent ion relative abundance is esentially constant from 10^(-6) to 10^(-4) torr. The fragment ion of mass 43 is the predominant primary ion at the argon resonance lines, and reacts to form ions of mass 41, 57, and 59. Double resonance is used to determine the reaction sequence of the major ions. At 10^(-4) torr, there is less than 2% of the proton bound dimer in propylene oxide, while in acetone or propanal the proton bound dimer is the major product ion. Preliminary photolysis results on propylene oxide suggest a chain process is involved converting propylene oxide to propanal.