Metastable transitions

Mass spectrometry has generally been employed in this series of compounds mainly for routine structure determination. The fragmentation pathways of some derivatives of 43 have been studied using accurate mass and metastable-transition measurements <1997JHC435>. 

Evers, E.A.I.M. Noest, A.J. Akkerman, O.S. Deconvolution of Composite Metastable Peaks a New Method for the Determination of Metastable Transitions Occurring in the First Field Free Region. Org. Mass Spectrom. 1977, 72, 419-420. 

Role of Electronic Structure in the Susceptibility of Metastable Transition-Metal Oxide Structures to Transformation... 

A technique specific to reflectron time-of-flight mass spectrometers where product ions of metastable transitions or collision-induced dissociations generated in the drift tube prior to entering the reflectron are m/z separated to yield product ion spectra... 

Figure 16.28—Metastable peaks. The figure shows the three masses involved in a metastable transition. The relationship between these three masses is given in the above text.

Figure 16.29—Metastable peaks observed in the mass spectrum of theobromine. The molecular ion (180 Da) loses the CONH radial (43 Da) giving rise to an ion at 137 Da. This fragmentation is accompanied by a metastable peak at 104.3 Da. The fragment at 137 Da further decomposes by loss of CO (28 Da) to yield a second metastable transition observed at a mass of 86.7 (Reproduced by permission of Kratos.)...

The electron impact-induced decomposition pathways of several structurally related /u.-methylene complexes of cobalt, rhodium, manganese, and iron have been elucidated by high resolution measurements, analysis of metastable transition (DADI linked scan), and 2H labeling (46). Terminal carbonyl ligands are generally lost prior to further fragmentation of the three-membered frameworks. Subsequent rearrangement reactions of the... 

This paper consists of three parts. The first part describes the high pressure synthesis of bimetallic compounds of NbN and MN where M is a Group 13 metal such as Al, Ga, or In. The second part discusses crystal structure investigations of a series of alkaline earth and transition metal nitrides, carried out to understand the bonding surrounding the transition metals. The third part describes the preparation of new metastable transition metal nitride and their solid solutions by rf-sputter deposition. 

Winters and Kiser have reported appearance potentials and cracking patterns for Ni(CO)4 (243), Fe(CO)5 (243), and the Group VI hexacar-bonyls (244). These carbonyls fragment by a series of consecutive uni-molecular reactions with loss of neutral CO groups. Support for this scheme came from an investigation of the metastable transitions in the spectrum of Fe(CO)5 (242), which were observed for the following processes ... 

The metastable transitions suggest that the fragmentation pattern of the tetramethyl derivatives follows Scheme 1, where HEMe2+ and H2EMe+ are very minor fragments in the spectra. 

Interestingly enough, both the Sn and Pb derivatives reveal very strong bare metal ion peaks. Other less important metastable transitions have also been well characterized in... 

The presence of longer alkyl chains or aromatic rings as substituents may provide the opportunity for rearrangements to take place. They are dominant at low energy and generally appear as metastable transitions in standard or MIKE spectra. 

Ion Processing. As mentioned, MS/MS began with the study of metastable ions (5j. Metastable transitions are observed from ions which undergo a dissociation while in transit through the instrument. The transition is a chemical reaction characteristic of the nature of the ion. In MS/MS, the instrument is modified so that the reactions occur more frequently and the masses of the reacting ion and the product ion can be established. 

---