Mass Spectra at Low Ionizing Voltage and Bond Dissociation Energies of Molecular Ions from Hydrocarbons

Abstract

Relative yields of parent and principal fragment ions from four paraffins and olefins by electron impact are measured for the first time. The characteristic features of the ion yields can be classified into four types related with the ionizing voltages. The decomposition processes for some fragment ions can be explained under some assumptions, and those for forbidden ions C2H5+ from isobutane and cis-2-butene under the assumption of hydrogen rerrangement.

Ab Initio Computation of Energy Deposition During Electron Ionization of Molecules

“…In addition to quantitative predictions for specific molecules, the BEB-derived energy deposition function can explain the widely known, if poorly documented, observation that EI mass spectra of organic compounds are sensitive to the electron energy below ∼20 eV but show relatively little change as the electron energy increases beyond 25 or 30 eV. ,− The rate of change of the EDF, eq , with respect to the incident electron energy ( T ), can be assigned a numerical value by using a metric such as D or L to measure changes. If X is the metric used to measure the distance between two normalized EDFs, then the rate of change of the EDF can be denoted d X /d T and defined by eq .…”

Experimental ion mobility measurements in pure iC4H10 and Ar-iC4H10 mixtures

“…In table 2, the possible reactions resulting from electron impact in iC 4 H 10 for electron energies of 25 eV, together with the appearance energies and their product distribution of the different ions are summarized. The probabilities indicated for the product distribution were estimated from data in [25].…”

“…The primary ions originated in the mixture are expected to be the same as in pure iC 4 H 10 since the ionization potential of Ar (15.82 eV [22]) is much higher than that of iC 4 H 10 (10.74 eV [25]). From the total electron impact ionization cross-sections for Ar and iC 4 H 10 and energies up to 25 eV, only for high Ar concentrations (above 82%) is the formation of Ar primary ions favoured.…”

“…Ionization products, appearance energies (A. E.) for ions formed in C 4 H 10 and the expected product distribution in iC 4 H 10 for electron impact ionization at 25 eV[25].…”

Mass Spectrometry

“…Fritz et al (196) investigate the mass spectra of silicon methylene compounds. Omura (379) gives the mass spectra at low ionizing voltage and the bond dissociation energies of the parent and principal fragment ions of ethane, propane, n-butane, isobutane, ethylene, propylene, 1-butene, and ds-2-butene. Ryhage and Stenhagen (480-432) re- port on the mass spectra and interpretations of processes forming the most intense ions in 69 methyl esters of organic acids.…”