Appearance Of Fragment Ions Research Articles

Trapping of positive ions in the electron beam of an ion cyclotron resonance spectrometer

Trapping of positive ions in the space charge of an electron beam is observed in the drift mode of an ion cyclotron resonance spectrometer at emission currents above 1 μA. This phenomenon is evident in two observations not normally seen in the ICR drift mode: (1) the appearance of product ions from ion-molecule reactions at pressure below 5 × 10 −7 torr using moderate drift potentials; and (2) the appearance of fragment ions occurring below thermodynamic threshold arising from electron impact dissociation of precursor parent ions. Trapping efficiency is found to increase with increasing emission current, decreasing electron energy, and decreasing source and trapping plate potentials. The implication of these results are discussed.

Electronic states of the radical cations of the 1,3-dipoles: HCNO, CH 2N 2, and N 3H, studied by photoelectron spectroscopy

The electronic states of the radical cations of HCNO, CH 2N 2, CO 2N 2, N 3H and N 3D, produced by photoionisation with HeIα(584 A) and HeIIα(304 A) radiation, were studied by photoelectron spectroscopy. The bands in the spectra observed, up to 25 eV ionisation energy, were assigned to the doublet electronic states of the cations by comparison with the data of the isoelectronic 1,3 dipole N 2O, ab initio calculations, band profiles and vibrational fine structure discernible. THe frequencies of the vibrational modes excited in the ground and two, or more excited states of the cations are presented. The inferred valence electronic configurations are · 6σ 2 7σ 2 1π 42π 4 for HCNO, · 6a 1 21b 2 21b 1 27a 1 22b 2 22b 1 2 for CH 2N 2 and ·6a′ 21a″ 2 7a′ 2 8a′ 2 9a′ 2 2a″ 2 for N 3H. The fragment ion appearance potential data on CH 2N 2 and N 3H are considered in view of the present energy data of the electronic states of their cations.

Application of Molecular Orbital Calculation to Fragment Ionization Processes in Ethanol and Ethylamine

Applicability of the MO interpretation for the phenomena of fragment ionization processes in ethanol and ethylamine has been studied. The double maxima of the C2H4OH+ ion and of the CH2OH+ ion, which are not easily accounted for by the quasi-equilibrium theory, were well explained by our molecular orbital calculation. It was also found that appearance of fragment ions and that of the band in photoelectron spectra in these substances are correlated to each other. From these results it was confirmed that bond scission occurs at the bond at which the electron is ejected.

Total and Dissociative Charge Transfer of Positive Ions with Perfluoroalkanes Studied by Mass Spectrometry

Total and dissociative charge-transfer cross sections of rare gas and molecular positive ions with CF4, C2F6, C3F8, n-C4F10, and cyclo-C4F8 are reported. The positive ions had an average energy of 50 eV so an electron jump mechanism occurs. When the total cross sections are plotted against the projectile ion recombination energy pseudoresonance effects are seen. It is suggested that the total cross section depends on the Franck—Condon factors for the transition of the neutral target molecule to a vibrationally excited ion. Thus higher vibrational states are less probable since they are generally associated with lower Franck—Condon factors. The highest cross sections occur with N2+. For a given projectile ion the total cross sections increase with the molecular weight of the fluorocarbons. The dissociative cross-section data indicates fragment ion appearance potentials in remarkably good agreement with recent photoionization measurements except for CF3+ from CF4.