SRC Users' Meeting - Synchrotron Radiation Center - University of ...

THE P(1s) AND P(2p) XAFS SPECTRA OF ELEMENTAL
PHOSPHORUS, THEORY AND EXPERIMENT
Astrid Jürgensen
Canadian Synchrotron Radiation Facility, Synchrotron Radiation Center,
3731 Schneider Drive, Stoughton, WI, USA 53589-3097
X-ray absorption spectroscopy was used to study the local structure and chemical bonding of
elemental phosphorus. Three allotropes of this element exist in the solid state. Crystalline black-
P, a semiconducting material with an orthorhombic puckered layer structure, is the most stable
allotrope. White-P, the least stable allotrope, is composed of tetrahedral P 4 molecules. At room
temperature it is a plastic crystal. Its structure is similar to -Mn with the P 4 molecules in the
positions of the Mn atoms. The most common allotrope is the amorphous red-P. Like white-P it
is composed of P 4 molecules. In the gas phase tetrahedral P 4 molecules are stable up to ~ 800 ºC.
At higher temperatures they decompose into P 2 molecules that have a shorter P-P bond length
and, like N 2 , a formal triple bond.
Theoretical P(1s) and P(2p) XAFS spectra of gaseous and solid state phosphorus were
calculated by ab initio FEFF and GSCF3 methods. These were compared and the spectral
features were related to structural and electronic properties of the different allotropes of
elemental phosphorus. The calculation results were then used to explain the features observed in
the experimental P(1s) and P(2p) spectra of red-P, which were obtained at the DCM and
Grasshopper beamlines of CSRF, respectively. They were measured simultaneously by total
electron yield (TEY) and fluorescence yield (FY) with the incident photon beam at normal
incidence to the sample surface.
The results of this study were presented at the XAFS 12 conference, held in Malmö, Sweden in
June of 2003. A paper has been submitted to Physica Scripta to be published in the conference
proceedings. A temperature dependent P(1s) EXAFS study of red-P is in progress to determine
the Debye-Waller factor (the mean square deviation of the interatomic distance) of the first
coordination shell in red-P.
0.1
0.05
0
-0.05
-0.1
3 6 9 12 15
P4 molecule
theory
0 1 2 3 4 5 6
0.35
P4 molecule
0.28
theory
0.21
0.14
0.07
(k)
0.1
0.05
0
-0.05
-0.1
0.1
0.05
0
-0.05
-0.1
white-P
theory
black-P
theory
FT(k 3 (k)) (Å -4 )
0
0.28
0.21
0.14
0.07
0
0.28
0.21
0.14
0.07
white-P
theory
black-P
theory
0.1
0.05
0
-0.05
red-P
experiment
0
0.12
0.09
0.06
red-P
experiment
-0.1
0.03
3 6 9 12 15
k (Å -1 )
0
0 1 2 3 4 5 6
R (Å)
The experimental P(1s) (top) and P(2p)
(bottom) XANES spectra of red-P
The P(1s) EXAFS spectrum (left) and its Fourier Transform (right). The first
peak in the FT represents the first coordination shell with an interatomic
distance of 2.212 Å.