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The geometry of a Hitachi RMU-7M double-focusing mass spectrometer was reversed by interchanging the positions of ion source and electron multiplier. The high resolution comparable to the “normal”instrument having Nier-Johnson type geometry can beobtained by using the modified instrument. This result makes it possible to measure metastable ion(MI)and collisional activation(CA)spectra and high resolution mass spectra on the same instrument by simple modification of the commercial instrument. The CA and MI spectra of the isomeric C8H8O+ ions generated from valerophenone and acetophenone were measured and discussed from a point of view of the ion structures.

Collisional activation spectra have identified (i) as Stable ion structures. Evidence is presented for a variety of pathway for their formation, including anchimeric assistance and hydrogen migration in less stable isomers. The fragmentation behavior of a number of [CnH2n+1O]+ isomers of n = 2 to 5 shows that extensive rearrangements are common, but that some reactions appear to be useful for ion structure elucidation. One reaction identified is unusual in that it represents the decomposition of an even-electron ion to yied an odd-electron ion product in significant abundance.

We have recently described1,2 a self-training interpretive and retrieval system (STIRS) for computer interpretation of mass spectra which utilizes directly data of all available reference spectra, and does not require prior spectra/structure correlations of these data either 'by human or computer effort. The computer selects different classes of data known to have high structural significance, such as characteristic ions, series of ions, and masses of neutrals lost, from the unknown mass spectrum, and matches these against the corresponding data of all the reference spectra. The reference compounds of closest match in each data class are examined for common structural features; criteria have been determined so that such features can 'be identified with approximately 95% relia'bility. Each reference compound has been coded in Wiswesser Line Notation (WLN) to make possible computer recognition of structural features. Further details of the initial system are available.1,2