A mass spectrometer was used to observe directly the contents of a flow reactor in which diborane at low pressure was being pyrolyzed. Temperature, flow time, surfaces, and gas pressures were varied. Borane, BH3, was clearly identified and its mass spectrum measured. A novel method, involving the difference in reactivities of monomer and dimer, was used to distinguish between BHX+ ions due to neutral borane and to fragmentation of diborane.(10) E.

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The intermediates produced in the pyrolysis of "B4Hi0 were studied with an "integral furnace" mass spectrometer with reactor temperatures between 10 and 285°. The reactor pressure of B4H10 was ca. 10~5•2 atm. B4H8 was identified as an intermediate produced in the pyrolysis. Diborane as well as a combination of pentaboranes (B5H8 and B5Hn), hexaborane, a combination of heptaboranes, octaborane, decaborane, and possibly nonaborane also were observed. Monoborane and triborane were not observed, but quantities small compared to B4H8 could not be excluded.

The mass spectra of "B4H10, "B4Dl0, specifically labeled *Bl0B3Hlo, and p-loB4H9D have been obtained under zero ion source contact conditions using a specially designed mass spectrometer and compared with spectra obtained previously on conventional spectrometers. In the latter case there are significant contributions to the spectra from neutral species formed by pyrolysis of tetraborane in the ion source, which acts as a flow reactor. A parent peak and several new metastable transitions have been observed in the zero source contact spectra. Analysis of an IlBlabeled tetraborane, *Bl0B3Hlo, has shown that the BlH,+, B*H,+, and B3H,+ fragment ions are formed in part by nonrandom dissociation processes of the B4Hz+ framework. A reinvestigation of the process by which hydrogen atoms are lost leading to the formation of B4H,+ ions does not appear to support the earlier proposed specific fragmentation scheme. The reaction of nB,De with nB,Hlo at 45' has been reinvestigated using nmr and gas volumetric techniques. No evidence for specific deuterium labeling is found. Pentaborane was formed.he mass spectrum of tetraborane-I0 has been re-

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