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observed peak heights for Mo 2F9 '. 'I'his, with the
observed precision of the analyses of the various
families of peaks, gives a satisfactory level of
confidence in the applicability of mass spectral
information to the molybdenum fluoride studies.
Sample 111, MoF,, yielded the spectrum shown
in Fig. 11.4 at 125OC. The presence of MO~F',~
is attributed to Mo,F, rather than to dimeric
MoFS, since Mo,F, is a reported compound which
could be expected to yield a parent ionic species
in the spectrometer. The Knudsen cell with the
sample in it was removed from the vacuum system,
exposed to air for 11 hr, remounted, evacu-
2
ated, and heated. No species was observed until
a temperature greater than 45OOC was reached.
A scan at 525OC was macle which yielded the spectrum
shown in Fig. 11.4. The sole parent species
yielding this spectrum appeared to be Mo0,F2.
Cracking patterns have been derived for the
various species primarily based on scans in which
the dominant or sole species was well character-.
izcd. Since MaF, has not yet been studied in our
equipmerit, we have assumed the applicability of
the reported data (see 'Table 11.2). Our derived
cracking patterns are shown in this table. The
compound designation for MoOF, is uncertain
(MoOF, is possible as far as we know). The cornpound
designated Mob', may be a mixture of MoF,
and perhaps 5 to 10% MoF .
The observation of Mo,#,' at temperatures of
325OC and of MoF, at temperatures up to 725'C
is rioieworthy. The compound Mo,P;, is reported to
decompose completely at 2OOcC, and MoF, is reportedly
not stable at the temperatures at which
we have observed it. One may, therefore, infer that
the free energies of fornation of these fluorides
per fluorine atom are so nearly equal that kinetic
factors are expected to dominate the descriptive
chemistry of these substances.
146
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MO~FS+
1 1 1 1
ORNL-DWG 67-1034ZR
ISOTOPIC PATEHN AT ~ZYC
I 1 /I
CaLCULAfED ISOTOPIC PATTFRN
FOR Mo2Fgf
3 5 3
amu
'0 375
Fig. 11.3. Comparison of Calculated and Observed
Isotopic Ataundunce for the Dimer Mo2F9.