419s
JOYCE
J. KAITFMAN, M v . S. KOSKI,I,. J. K u r r ~ sA N D R.117. LAW
1-01. 54
[CONTRIBUTION FROM RIAS,7212 B ELLONA XVE.,BALTIMORE, MARYLAND, THE DEPARTMEKT OF CHEMISTRY, THEJOHNS HOPKINS USIVERSITY,BALTIMORE 18, MD., AND THE CALLERY CHEMICAL COMPANY, CALLERY,PENNSYLVANIA 1
Appearance and Ionization Potentials of Selected Fragments from Decaborane,
B 11ioHi41 BY JOYCE J. KAUFMAN, W. S. KOSKI,L. J. KUHNSAND R. 'IV. LAW RECEIVED APRIL19, 1962 The appearance potentials of selected ions from decaborane B1110H14 (99.68% B") were measured by mass spectroscopy. X set of apparently self-consistent ionization potentials for decaborane and various BIoH, fragtnents were calculated from
these appearance potentials, using what little therniochemical bond energy data are available, combined with the authors' interpretation of the processes taking place on ionization and fragmentation. An IBM 7090 computer program t o calculate monoisotopic fragmentation patterns from mass spectral raw data was written. From the mass spectrum of B111aH14 at 70 ev. the monoisotopic fragmentation pattern of decaborane was calculated. For comparison, from mass spectral raw data a t 70 ev. of decaborane containing normal isotopic abundances of BI0 and B", several different monoisotopic fragmentation patterns of decaborane were calculated which varied depending upon the method of choice of the original % B1o in the molecule.
The progress on the electron impact induced Experimental dissociations and ionizations of boron compounds is The instrument used to measure the appearance potena t about the same stage now as the work on electron tials of the decaborane and its fragments was a Consolidated impact studies of the hydrocarbons was twenty 21-103B mass spectrograph modified for appearance poteritiaI work by use of a 150,000 ohm Helipot and a 200 ohm years ago, with two great added disadvantages. resistor inserted into the ionizing voltage circuit so that the First, naturally occurring boron contains ~ 2 0 7 ionizing ~ voltage could be varied from about 6 to 100 v. BIO and wS0GjO B1l. This means that the boron and measured accurately with the Leeds and Northrup 7885 potentiometer. Scanning was done over a small Model skeletons of every natural boron compound conrange of ion accelerating voltage with the magnet current tain all possible combinations of BIDand Bll atoms adjusted t o bring the ion of interest on the collector a t as governed by binomial distribution probabilities. 500 f 10 v. The voltage on the metastable suppressor For certain simple compounds such as the boron slit was zero. A sample of the gas t o be studied was adtrihalides, this boron distribution presents no mitted to the expansion bulb and then an internal standard (argon) was admitted until the signal from the calibrating problem. However, for all hydrogen-containing gas was equal to that for the ion of interest. The data were boron compounds, it is virtually impossible to treated in two ways: by means of a semilog plot of ion realize any meaningful results from appearance current versus apparent ionizing voltage2 and by using the as equal t o the voltage when the ion potential data unless one makes the completely appearance potential current was 1% of the current a t 70 ev.3 Using known BIO or B1l labeled compound starting from the BF3 spectroscopic values for the internal standard, a correction compound, which is the only usable source of was determined and applied t o the unknown, giving its appearance potential. The accuracy of the first method was labeled boron. verified hp measuring the appearance potential of CzH6+ Second, there are almost no available independ- from CzHBwhich checked to within 0.4 ev. higher than the ent thermochemical data from which to calculate spectroscopic value (the appearance potentials of ions are the energies of the possible states of combination in usually 0.2-0.3 ev. higher than spectroscopic ionization potentials). which the boron and other atoms may exist. The B1110H14was prepared by pyrolysis of diborane at The appearance potentials of selected ions from 12c50as previously described.4a decaborane, B111aH14(99.68% B 11), were measured Calculations and Results mass spectroscopically. A set of apparently selfA. Ionization Potentials.-The appearance poconsistent ionization potentials for decaborane and various BlaHnfragments were calculated from these tentials of decaborane and its fragment ions were appearance potentials using what few thermo- carried out on the B1'loH14 compound (containing chemical bond energy data are available, combined 99.68% Bll). The yo BIO in the molecule was with the authors' interpretation of the processes calculated from the ratio of m/e 10 to m/e 11, which leads to an upper limit for yo B'O. The use taking place on ionization and fragmentation. of the completely B" labeled compound was a -In I B M $090 computer program to calculate because i t would have been impossible monoisotopic fragmentation patterns from mass necessity untangle the appearance potentials due to ions spectral raw data was written. From the mass to of the same mass (containing either one less hydrospectrum of B1110H14 a t 70 ev. the monoisotopic frag- gen atom or else one BIO atom instead of one B*' mentation pattern of decaborane was calculated. atom in the boron skeleton of decaborane). Even For comparison, from mass spectral raw data a t for appearance potentials of ions from diborane 70 ev. of decaborane containing normal isotopic normal isotopic abundance of BIO abundances of B1° and B", several different rnono- containing and B11#4b it was not possible to determine to which isotopic fragmentation patterns of decaborane were an observed appearance potential corresponded calculated which varied depending upon the method ion a t any m/e value lower than the one corresponding of choice of the original Yo BIO in the molecule. (1) This research was supported i n part by the Directorate of Chemical Sciences, Air Force Office of Scientific Research, and in part b y the Office of Naval Research. Reproduction in whole or in part is permitted for any purpose of the United States Government. Presented in part before t h e Division of Inorganic Chemistry, 138th S a tional Meeting, -4merican Chemical Society, September, 1400.
(2) V. 11. Dibeler, R . M.Reese and F. L. Mohler, J . Res. N u l l . Biw. Slandaids, 57, 113 (1956). (3) J. B. Farmer, F. P. L o s i n g , D. G. H. Marsden and C. A. RlcDowell, J . Chem. Phys., 24, 52 (1956). (1) (a) Joyce J. Kaufman a n d W. S. Koski, J . A m . Chem. SOL.,7 8 , ,5774 (19.56). (b) W. S. Koski, Joyce J. Kanfnian, C. F. Pachii
