Colussi, A. J.

Fessenden, Richard W.

Morton, J. R.

Preston, K. F.

Caltech Authors - Main

ESR spectra of PF2 and SF3 radicals
A. J. Colussi, J. R. Morton, K. F. Preston, and Richard W. Fessenden 
 
Citation: The Journal of Chemical Physics 61, 1247 (1974); doi: 10.1063/1.1682004 
View online: http://dx.doi.org/10.1063/1.1682004 
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/61/3?ver=pdfcov 
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NOTES 
ESR spectra of PF2 and SF3 radicals *t 
A. J. COlussi+, J. R. Morton, and K. F. Preston 
Division of Chemistry. National Research Council of Canada. Ottawa. Canada 
Richard W. Fessenden 
Radiation Research Laboratories and Center for Special Studies. Mellon Institute of Science. 
Carnegie-Mel/on University. Pittsburgh. Pennsylvania 15213 
Several years ago two of the present authors reported 
almost simultaneously the detection and identification of 
the radical PF 2 by ESR spectroscopy. Fessenden and 
Schuler1 detected the radical during irradiation at -135 
DC of nominally pure SF 6 with 2.8 MeV electrons, and 
found its spectrum to be considerably enhanced by the 
addition of small quantities of PFs. Wan, Morton, and 
Bernstein,2 on the other hand, detected the radical in y-
irradiated ND4PF 6' The parameters describing this 
latter spectrum were g=2.0108±0.0002, ap=36.0 
± 0.5 G, and aF = 60.5 ± 0.5 G. In 1970, Wei, Current, 
and Gendells also claimed to have observed the ESR 
spectrum of PF 2 formed by the thermal decomposition 
and photolysis of P2F 4 and PF 2H. In spite of discrepan-
cies in the g values, there was no suggestion that the 
earlier work1,2 was suspect until Nelson, Jackel,and 
Gordy4 obtained an isotropic spectrum of PF 2 by y ir-
radiation of PF 3 trapped in a xenon matrix. Their pa-
rameters were quite different from those of preceding 
workers, g = 2. 0020, a p = 84. 6 G, and aF = 32. 5 G. 
In order to resolve the issue we have sought new and 
unequivocal methods of preparing the radical PF2: (a) 
The irradiation of 5 mole% PF s in a C2F 6 matrix with 2.8 
MeV electrons5,6 and (b) The UV photolysis of PF2Cl in 
the liquid phase. 7 Both of these methods were success-
ful, and yielded ESR spectra of PF2 whose parameters 
(Table I) were consistent with those of Nelson, Jackel, 
and Gordy. Unfortunately our1,2 previous identifications 
of the radical appear to have been incorrect. It would 
appear that Wei, Current, and Gendell3 had also detected 
PF2, although it was probably incompletely frozen into 
the matrix. Specifically, we feel that their "perpendicu-
lar" features might well be due to freely rotating radi-
cals, suggesting the following isotropic parameters for 
PF 2 in an argon matrix, g = 1. 9922, ap = 83.0 G, and aF 
=33.5 G. 
Wan, Morton, and Bernstein's radical is almost cer-
tainly P02F 2' It has already been shown8 that NH4PF 6 is 
susceptible to hydrolysis, and doubtless some conver-
TABLE 1. ESR parameters of PF2 in (a) C2FS 
matrix at -140°C and (b) in PF2Cl dissolved in 
Freon 13 at -100°C. 
(a) 
1. 9994 ± O. 0003 
81.3±0.2 G 
33.1±0.2 G 
(b) 
1. 9997 ± 0.0001 
82. O± 0.1 G 
32.4±0.lG 
sion to ND4P02F2 occurred during the deuteration pro-
cedure. Furthermore, Begum, Subramanian, and 
Symons9 have reported parameters for P02F 2 (g = 2. 0100, 
ap = 43.8 G, and aF = 52. 5 G) which are similar to those 
of the radical detected2 in irradiated ND4PF 6' 
The radical labelled PF2 by Fessenden and Schuler
1 
must also be reidentified. Since its spectrum can 
be observed when purelO SF 6 is irradiated, it must arise 
from a sulfur-centered radical, now believed to be SFs. 
The spectrum of SF s is considerably enhanced by cer-
tain additives, notably PFs. For example, the inten-
sity of the published spectrum1 (1% PF s in SF 6) is ap-
proximately ten times stronger (relative to thatll of SF 5) 
than that observed in irradiated pure SF6• The PFs 
seems either to partiCipate in reactions involving SFs 
or to modify the matrix to make stabilization of SF 3 more 
likely. 
The radical SF s is the prototype of certain sulfanyl 
radicals which have recently been studied. 12 These 
radicals, of the general type (RP)sS, where Rf=CFs or 
SF 5, possess two equivalent ligands whose (19F ) hyper-
fine interactions exceed those of the unique ligand. In 
other words these derivatives of SFs do not possess a 
threefold axiS, but a plane of symmetry. Consequently 
one would also expect SF 3 to exhibit a spectrum showing 
hyperfine interactions with two equivalent 19F nuclei, 
and a somewhat smaller interaction with a unique 19F 
nucleus. The parameters in Table II a, which were ob-
tained from the aforementioned spectrum, accord very 
well with these deductions. 
We have also succeeded in observing the spectrum of 
SFs in the liquid phase, by photolyzing a solution1S of 
H2S or D2S and CF sOF in Freon 13 at -110 DC. The 
spectrum of SF s, whose parameters appear in Table II b, 
persisted for only a few minutes. It is curious to note 
that the hyperfine interaction of the two equivalent 19F 
nuclei is slightly less in solution than in an SF 6 matrix, 
presumably the result of a slight change in the radical 
geometry. 
TABLE II. ESR parameters of SFa in (a) SF6 matrix at -135°C 
and (b) Freon 13 at -110°C. 
g 
aF(one nucleus) 
aF(two nuclei) 
(a) 
2. 0054± O. 0001 
40.4± 0.1 G 
54.3±0.1 G 
(b) 
2.0050 ± O. 0001 
41. O± 0 •. 1 G 
48.7 ±0.1 G 
The Journal of Chemical Physics, Vol. 61, No.3, 1 August 1974 Copyright © 1974 American Institute of Physics 1247 
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1248 Letters to the Editor 
*NRCC No. 14127. 
tWork supported, in part, by the U. S. Atomic Energy Com-
mission. 
tNRCC Postdoctoral Fellow 1974. 
!R. W. Fessenden and R. H. Schuler, J. Chern. Phys. 45, 
1845 (1966). 
2J. K. S. Wan, J. R. Morton, and H. J. Bernstein, Can. J. 
Chern. 44, 1957 (1966). 
3M. S. Wei, J. H. Current, and J. Gendell, J. Chern. Phys. 
52, 1592 (1970). . 
4W. Nelson, G. Jackel, and W. Gordy, J. Chern. Phys. 52, 
4572 (1970). 
5The experimental technique was similar to that described in 
Ref. 1. Solid C2F 6 (m. p. - 94°C) allows free rotation of small 
radicals down to about -165°C as shown by the isotropic 
spectra observed for CF3 and C2F5 in this matrix (R. W. 
Fessenden and R. H. Schuler, J. Chern. Phys. 43, 2704 
(1965) and in Advances in Radiation Chemistry, edited by M. 
Burton and J. L. Magee (Wiley-Interscience, New York, 
1970), Vol. 2, p. 90. 
6In addition to the ESR lines of PF2 there were lines of PF4 (the 
same spectrum as in SF6!) and weak lines of C2F5. 
7J. G. Morse, K. Cohn, R. W. Rudolph, and R. W. Parry, 
Inorganic Syntheses, edited by E. L. Muetterties (McGraw-
Hill, New York, 1967), Vol. 10, p. 153. 
SR. W. Fessenden, J. Mag. Res. 1, 277 (1969). 
9A• Begum, S. Subramanian, and M. C. R. Symons, J. Chern. 
Soc. A 1970, 1323. 
!OMass spectroscopic analysis of the SFs used in that work 
shows CF4 to be the only Significant impurity (~1%) and that 
PF3 cannot be present to over about 0.01 mole%. 
I1This spectrum was originally aSSigned by Fessenden and 
Schuler! to SF/. See J. R. Morton and K. F. Preston, Chern. 
Phys. Lett. 18, 98 (1973) for the present assignment. 
!2J. R. Morton and K. F. Preston, J. Phys. Chern. 77, 2645 
(1973). 
!310~1 each of liquid H2S and CF30F, separated by 100~1 of 
Freon 13, were allowed to warm up to - 96°C. If the sample 
did not explode, the spectrum of SF3 could be detected upon 
photolysis at -110°C. 
J. Chern. Phys., Vol. 61, No.3, 1 August 1974 
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ESR spectra of PF_2 and SF_3 radicals

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ESR spectra of PF_2 and SF_3 radicals

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