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INNER SHELL RESONANCES IN
PHOTOABSORPTION SPECTRA OF GAS PHASE SILICON COMPOUND MOLECULES
S. Bodeur, I. Nenner
To cite this version:
S. Bodeur, I. Nenner. INNER SHELL RESONANCES IN PHOTOABSORPTION SPECTRA OF
GAS PHASE SILICON COMPOUND MOLECULES. Journal de Physique Colloques, 1986, 47 (C8),
pp.C8-79-C8-82. �10.1051/jphyscol:1986813�. �jpa-00226029�
JOURNAL D E P H Y S I Q U E
Colloque C 8 , s u p p l 6 m e n t au no 12, T o m e 47, d 6 c e m b r e 1986
INNER SHELL RESONANCES IN PHOTOABSORPTION SPECTRA OF GAS PHASE SILICON COMPOUND MOLECULES
S . BODEUR* and I . NENNER* *
* ~ a b o r a t o i r e d e Chimie-Physique, 1 1 , rue Pierre et Marie Curie, F-75231 Paris Cedex 0 5 , France
"CEA-IRDI/DESICP, Departement de Physico-Chimie, CEN-Saclay, F-91191 Gif-sur-Yvette Cedex, France
LURE, Laboratoire commun CNRS, CEA et MEN, Bstiment 209 D , Universitg de Paris-Sud, F-91405 Orsay Cedex, France
Nous avons mesurd les spectres de photoabsorption des moldcules Six4 (X = H, F, CH C1) dans la rggion du seuil Sils (1840-1900 eV). Des rgsonances intenses sont obser- 3 vdes dans les parties discrbtes et continues du spectre. L'interprdtation est faite sur la base des propri6tGs Qlectroniques et structurales des espsces "1 coeur dqui- valent" : les radicaux phosphoranyles PX4 et aussi en termes de rdsonances de forme.
Abstract :
Photoabsorption spectra of Six molecules (X = H, F, CH and C1) have been measured
4 3
near the Sils edge (1840-1900 eV energy range). Intense resonances are observed in the discrete and the continuum part of the spectra. They are interpreted using elec- tronic and structural properties of the core equivalent phosphoranyl radicals PX
and also in terms of shape resonances. 4
Introduction
Most resonances observed in inner shell photoabsorption spectra of an isolated mo- lecule originate from transitions of a core electron into an antibonding valence, Rydberg or continuum orbital. Their nature is expected to vary drastically when the absorbing atom is bonded to different ligands. In order to analyse these effects, we report the first photoabsorption measurements in the silane molecule, SiH near the silicon 1s edge. We analyse the specific molecular effects by comparison with 4 the isoelectronic argon atom. We compare the observed resonances with those found recently(]) in the Sils photoabsorption spectra of other Six molecules (X = CH3, F, Cl). Special emphasis is put on couplings between electronic and nuclear motion 4 i. e. the Jahn-Teller effect.
Experimental
Synchrotron radiation from the ACO storage ring at LURE, Orsay,is dispersed by a double crystal monochromator equipped with two InSb (111) cryssals (2d =
7.46 li). One obtains a photon beam with an intensity of the order of 10 ph/s in a 0.4 eV band-pass around 1850 eV. This monochromatic beam passes through a gas cell equipped with 1 ym polypropylene windows. The intensity of transmitted X-ray beam is ensured by a flow proportional counter. More details on the experimental set-up and data recording can be found in ref.2
.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986813
JOURNAL DE PHYSIQUE
Results and discussion
We present in fig.] the photoabsorption of SiH measured in the 1838-1870 eV energy range. We have indicated the Sils core ionization energy as measured by XPS (3) 4 which separates the discrete and continuum spectrum. We have interpreted the dis- crete spectrum by comparing it with the Argon atom, both around the Is edge (fig 2) and the 2p edge (fig 3). The important broadening of resonances in the Is compared to the 2p spectra (Ar and SiH4) originates Irom the core hole lifetime which is about ten times shorter 5 r 1s than for 2p. Tbe ?.ydberg series identiCiec? in t5e Is lectron study of SiH (11). One expects a broad Pranck-Condon (F.C.) envelope in contrast to a Rydberg state for which+the potential energy surface is bound in the 4 F.C. zone in close resemblance to SiH4 (core hole). However, the combination of the Si 1s short lifetime with the F.C. envelope is not sufficient to explain the extremely large broadening of the & (t2) resonance. We believe that another effect is present as discussed below.
The interpretation of the continuum ismore straightforward. Line 3 in Fig. 1 is pro- bably a doubly excited state in which a valence excitation is present in addition to
the core hole. The absence of any shape resonance is readily explained by the extreme- ly small perturbation caused by the hydrogen atoms on the silicon, in this respect, SiH& is very similar to both argon and the silicon atom cases.The same conclusions have been obtained by Pavlychev et a1 (14) when analyzing the Si 2p photoabsorption
spectrum of silane.
The substitution of the H atoms by other ligands (F, CH3, C1) greatly perturbs the spectra (I) as illustrated in Fig. 4 for SiF4. In the dlscrete spectrum a weak transi- tion into the electric dipole forbidden a l is seen. More importantly, a strong doublet dominates the spectrum whereas Rydberg lines are absent. Because a unique
8
(t2) is expected (15) as for SiH4, we have offered (1) an interpretation based on the core equivalent species PF4. The PF ground state is known (10) to be stable in distorted geometries (Fig. 5) in one of the trigonal bipyramidal (TBP) arrangements C 4 or C One expects a very large potential energy barrier between potential energies at te2~;- 2v hedral and TBP geometries. The existence of this barrier combined with the degenerate character of o* (t ) states have led us to analyse the spectrum in terms of a Jahn- Teller effect (16~~17). This results from a vibronic coupling which departs from the Born-Oppenheimer approximation. It involves the active Jahn-Teller modes vJT. In the strong coupling case, a large broadening and even a splitting AE of the line maobserved. This splitting AE is related to the potential barrier B by AB = 2v JT
Se
for which D = B/vJT. It is likely that barriers of a few eV are necessary to explain TABLE 1
-
Experimental and theoretical term values (eV) of Rydberg and/or valencetransition in core photoabsorption spectra of argon and silane.
Rydberg valence cr
*
4 s a
*
1 t; 4 P
5~
5 s
3d 3d (el 3d(t2) Core ionization limit (ev)
1s or 2p (312,112)
Argon core excitation -
Ar 1s Ar 2p theory r e f 3 r e f 5 r e f 8 4.4 4.4 3.99
- -
- -
2.7 2.73 2.60
1.25
-
- -
-
1.75 1.513202.9 248.7 250.8 ref 12 ref 5
SiH core excitation 4
Si Is Si 2p theory this work ref 7 ref 7 ref 8
- -
4.4 (4.04 4.2 3.4'0.5 3.4 2.85
1.720.5 2.14 2.5
-
2.2 1.63- {
1.91.6 'la99 1847.0 107.2 108.44
107.8
ref 3 ref 13 ref 7
Si F4 ie P.
TB P.
A This work
.
.z . . Slllcon K x*
0 z : :
. '..<
; v- .
c 3,
I I I c 2v
1844 1848 1852
PHOTON ENERGY ( e ~ )
Fig.4
-
S< 1s photoabsorption spectra o f F i 9 . 5-
Equato~iaZ fCZGJ and &a2S i p 4 from ref 2 . (C3J trigonaZ bipgrmzd a f t e r ref 10.
a 1.4 eV splitting of the t2 line seen in the Si Is SiF spectrum and the extra broa- 4 dening of the t2 line in the Si 1s SiH4 spectra. In contrast to SiH
,
there is no transferability of term values from one edge to another. Similar effects are found (1) in Si(CH3)4 but not for SiC14 for which the interpretation is still unclear at present.In the continuum, strong resonances are observed above the Si Is edge for the three molecules (1) as seen in Fig. 4. They are likely shape resonances originating from the large anisotropy of the molecular field.
We are thanking W.E. Schwarz for a critical reading of the manuscript. We are grate- ful to E. Lizon & Lugrin for his technical assistance and the LURE staff for general facilities.
REFERENCES
1
-
S. BODEUR, I. NENNER and P. MILLIE, Phys. Rev. A (in press) 2-
S. BODEUR and J.M. ESTEVA, Chem. Phys.100,
415 (1985)3
-
R.G. CAVELL and R.N.S. SODHI, J. Elect. Spect. Rel. Phenom.2, 145 (1979) 4-
L.G. PARRATT, Rev. Mod. Phys.2,
616 (1959)5
-
G.C. KING, M. TRONC, F.H. READ and R.C. BRADFORD, J. Phys. B Atom. Molec. Phys.10, 2479 (1977)
-
6
-
W. HAYES, F.C. BROWN and A.B. KUNZ, Phys. Rev. Lett.27,
774 (1971)7
-
H. FRIEDRICH, B. SONNTAG, P. RABE, W. BUTSCHER and W.H.E. SCHWARZ, Chem. Phys.Lett.
66,
360 (1979)8
-
W.H.E. SCHWARZ, Chem. Phys.9,
157 (1975),11,
217 (1975)9
-
F. KELLER and H. LEFEBVRE-BRION, Z. fiir Physik D Atoms. Molec.Clusters (in press) 10-
R.A.J. JANSSEN, G.J. VISSER and H.M. BUCK, J. Am. Chem. Soc.106,
3429 (1984)and ref therein
1 1
-
G.G.B. de SOUZA, P. MORIN andI.
NENNER, Phys. Rev. A (in press) 12-
J.A. BURDEN and A.F. BURR, Rev. Mod. Phys.2,
125 (1967) 13-
W.B. PERRY and W.L. JOLLY, Chem. Phys. Rev.11,
611 (1972)14
-
A.A. PAVLYCHEV, A.S. VINOCRADOV, T.M. ZIIKINA, D.E. ONOPKO and R. STSP~GAN, Opt. Spectrosc (USSR)5,
109 (1980)C8-82 JOURNAL DE PHYSIQUE
15
-
H. FRIEDRICH, B. PITTEL, P. RABE, W.H.E. SCHWARZ and B. SONNTAG, J. Phys. B Atom. Molec. Phys.13,
25 (1980)16
-
P. HABITZ and W.H.E. SCHWAEtZ, Theoret. Chin. Acta (Berlin)8,
267 (1973) 17-
C. COSSART-MAGOS, Proceedings of the XIXth Jerusalem Symposium in Quantum Chem.and Biochem. "Tunneling", 5-8 Mars 1986 (to be published in Reidel Pub. Co, Dordrecht, Holland;)
C. COSSART-MAGOS, D. COSSART and S. LEACH, Chem. Phys.
