Dissociation of Meta-stable Ions in Mass Spectrometers with Release of Internal Energy

Abstract

Certain of the "meta-stable peaks" in mass spectra are abnormally wide. This extra width is shown to be associated with release of kinetic energy during fragmentation. Methods are presented for measuring this energy release and values are given for various transitions in the spectra of aromatic nitro compounds.Meta-stable ions are often detected in the mass spectra of organic compounds 1* 2. These ions may be detected if they dissociate near the entrance slit of the magnetic analyser in sector magnetic field mass spectrometers. If ions of original mass ml dissociate to produce ions of mass m,, a peak appears in the mass spectrum at a position m ' where m*==m,2/ml. (1)These peaks are usually quite small and are mu& broader than peaks produced by normal stable ions. They often extend over a range of several mass numbers and usually have a shape resembling a GAussian distribution curve. Their maxima are usually sufficiently well defined to enable one to determine the values of mi and m e , from equation ( l ) , for the ions involved in the transition. Occasionally, however, some of these "meta-stable peaks" are observed to be much broader than usuaI and to have a relatively flat top. Theoretical ConsiderationsIn arriving at the approximate relationship of equation (1) , HIPPLE and his co-workers assumed that there was a negIigible release of kinetic energy during the dissociation. In such a case the kinetic energy acquired by an ion of mass ml during the acceleration process is shared on dissociation between the two resulting particles in proportion to their masses.Let us now consider an ion mi+ which is formed in the ionization &amber with zero kinetic energy and falls through a potential Yl before dissociating into an ion m2+ and a neutral fragment (ml -m,) , i.

Metastable ion fragmentation processes in n‐alkanes

“…It can be seen that the elimination of two hydrogens (probably in the energetically favoured form of molecular hydrogen) results in the now familiar broadened dish topped type of 'metastable peak', which indicates the release of a discrete amount of excess kinetic energy during the process. 15 The value of this excess kinetic energy release obtained by measurement of the width of the peak15.1G in Fig. 1 is 0.21 i 0.03 eV.…”

“…In the GEC/AEI MS-9 mass spectrometer with Nier geometry8 used in this study, the constant V/E is 15 and once established is maintained automatically for ion accelerating voltages from 1 to 8 kV. When an ion fragmentation m,+ -+ ni2+ + (m, -m,) occurs with no release of internal energy, the daughter ion m2+ has a fraction m2/rnl of the kinetic energy of the decomposing ion m,+.…”

Collisional activation spectra of organic ions

“…From the Massey "adiabatic criterion," (2KE/m)'/' = aAE/hZ2 (h is Planck's constaat), an interaction limit (adiabatic parameter, a) of 10 A predicts a most probable AE (for a broad range of values) of 0.6 eV for an ion of mass (m) 30 and 0.15 eV for one of mass 480 for an accelerating potential of 3.6 keV. In the CA spectra of the molecular ion of I-propanol (Table 11) the prod- F. W. McLAFFERTY ETAL.…”

Through a Glass Darkly: Glimpses into the Future of Mass Spectrometry

“…Unimolecular dissociation (QET, metastable ions) 20,30) Ion/molecule reactions 31) Dynamics and kinematics (energy partitioning) 32) Structural characterization of elusive chemical species 33) Ion structures and ion spectroscopy 34) Cluster ions 35) C-C and C-H bond activation 36) Ionic collisions and reactions with surfaces 23) 42) The various types of multiple-stage MS n experiments have been rationalized including multiple reaction monitoring MRM 43) and single reaction monitoring (SRM) experiments, lately so important in biological mass spectrometry. 44) We conclude this historical with a listing of 10 singular achievements in the history of mass spectrometry ( Table 4).…”