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Molecular orbital study of interactions of single transition metal atoms with C2H2 and C2H4
CIIL!UICAL
PHYSICS LETTERS
MOLECULAR ORBITAL STUDY OF lNTERACTlONS SINGLE TRANSlTION 1IirqwI.i
ktreived
15 October
1979
OF
METAL ATOMS WITH C2H2 AND C2H4
ITOH .md A. Bmy KUNZ
22 June 1979: in tina farm 20 JuIy I979
Interactions of single transttion metal atoms of I-c. Co. Ni .md Cu u ith C2II2 and CzII4 were studied by an ab initio MO theor)-. The magnitudes of the HOMO IcwI shifts at-both Iigands increase with atomic number. The results were compared aith .xtiI.rbIe absorption experiments.
! _ Introduction
2. Method and model
The interaction of~etylene (C2Hz) and ethylene (C2HI) with transition metal surfaces has been estensively studied by me.ms of many experimental methods including photoeiectron spectroscopy [l-3] _ It is well known that one metal catalyst is effectike in some catalytic reaction but is lery poor in another reac-
Ab initio restricted Hartree-Fock MO calculatiqns were performed. Effective potentials replacing the Ar cores of the transition metal atoms were employed [9]Then, only the 3d, 4s and 4p valence orbitals for the metal atoms were taken into account. The 3d functions were taken from ref, [IO] and were incremented with one s function of exponent 020, one p function of exponent 025 and one d function of exponent 0.20. The gaussian basis set contracted to a minimal basis set was used for H and C atoms [ 1 l]_ The present basis sets gave good orbital energies and electron populations to the metal complexes reported before [6-S] _ The z-bonded mode!s for complexes were adoptedThe free moIecuiar geometries for C,H, (Dmh symmetry) and CzH4 (Dzh symmetry) in the complexes were assumed_ The distance between the metal atom (M) and the C atom was taken as 2.08 A for both C2H2 and C2Ha complexes_ The Z-antis was taken 3s the perpen-dicular direction to the C-C bond.
tion.
The difference
of adsorptive
and tzttalytic
proper-
ties of metals should be explained. The present authors [4.5] reported MO calculations on adsorption of hydrogen and CO on Ni 2nd Cu metal clusters which explained the difference of adsorptive properties of Ni and Cu in relation to the difference of their Sd-band positions and the simiktrity of their 4s4p bands. Moreover, the present authors [6-S] hake reported db initio MO calculations of the interactions of singe transition metal atoms of Fe, Co, Ni and Cu with PF,,CO, N, , NZH,, NaH4 and NH, ligands. As general trends. the &hest occupied molecular orbit& (HOMO’s) of these ligands shift toward lower energy_ The magnitudes of the shifts increase in the order of atomic number. The purpose of the present paper is to apply an ab initio MO theory to interactions of the single transition metal atoms of Fe, Co, Ni and Cu with C2H, and C2H1 ligands and to compare calculated results with available experimental results on adsorption_
3. Resuits and discussion Since the electron configurations of the transition metals with tz vaIence electrons [ 121 were assumed to be 3dn-14si, only the molecular states with highest spin multiplicities derived from the M 3d”-14s1 con531
_ _ f-11
St
___
0.733 6.539 9 $37
~;~ttr.ttitms acre rr.ttcufrtzsd itt tftc presctrr sttttif. It! tabfe I. :hc 3d and 4s orbktt energies of the rr~nsition t!!etal atoms with 3~P-~lst cot!figttr;ltiot!s wfiich were cAxthred by Clettrenti ztnd Koetti ii31 ztre listed. It is sees! ths ;~kfxw& she 4s orbital et!egies It-e neariy indepet!denr of atomic number, tf!c 3d orbitat et!ergics
ctrttreza rqidly in the order of .ttomic nut!!bcr_ The 3d orbMs xc rerv locaked sot!spared with tlte 4s orbit&_ TI!e large dift~rencc between the single metsI atoms and the real tnetds is rh;tt the 4s orbit& are tire hi$!est energy fevefs in the si&e 3toi!!s, whife the 4s bat& oftnetrrls sprc.tJ ztbotre;tnd bdorv the 3d brmds. Next the nkttktted results wifl be represented. Since is! the compIexes of ti!c m&d atotns with tl!e closed she11mokctdes considered in this paper tI!e free ~!!oIe&e-like orbitais retain their ftce n!olecular chsracter. the notation for the free molecules is used to rrpresent ekctrcmic states of rhe complexes_ Whet! the metf atoms interact with these molecules, both the 3d orbitalisand the 3s orbit& of the metaf atoms interact con. sidembly with the Ei~artdorbit& independent of figand species as observed as the reduction of the n!etai 3d bands in the photoefecrron experimenrs on adsorption. The vaience mofecttkr orbitaf energies and efectron pop&&ions of M-C&ii2 complexes are shown in tibles 2 and 3.. From tztbie 9, it is seen tI!at the C,H7 Iike revels shift from their free C2H2 ones due toti!: bondins interaction of the C2H, orbit& with the
Table 2 Orbiti erter@s (in eV) of Sf-CzH2 Fe
CO
Ni
Ctt
-i3.00
-1327 --I4_15
-1317 -1451
-1959 -2190
-I9=II -22x)0
-14.35 -14.39
-14.41 -&I?
-3529
-3025
-13.50
-19-a -21-75 -2958
532
-1999 -22.23
-35-49
-3055
_ _ _I~
Ltrge bot!dtt!g ttr!d rtt!tibot!dit!g it!ter.tcttot!s between f\\o orbit& occur whet! energy difkrct!ce of them is ~t!.t11nt!d whett ovcri.q> of tl!e IWU orbirals is large_ Titer!. the I iru I&e kvei xihicl! is tile f fOM0 of C, I-f2 shifts towards Iowver energy white the orher let,& rimA A itctr1~ the sztrtir~crtergtes as thi: free C2 f 11? _ Tf!e preseer resuhs are consistent with the UPS q&iill~t!fS.
Table 2 shows ti!at tI!e originally dqencrsted 1nu Ievefs spltc into two levels due to the interaction rviti! tffe t!!ettll atoms. Tlieir seprtmtions .tre sniclll t-or tile Co at!d Xi compie~s. The energy shifts of the aver,gc of the spfitred IckeIs frrtm tf!e free C2H2 is, feteis are shown in t.tble 4. The experimental v.ducs are sko shown in tabIe 4. TI!e tnagnitude of the c&xtI.tted shift increases ix! tl!e order of atomic t!utnber because the met& atom 3d orbirrti energy decreases with the aton!ic number as seen from table f _ Tile calculated vrthtes for rhe Ki and Cu con!pIexes are in good agreement with the experiments. sttggestit!g that the geometry change of tile C,H, - _ tnofecule adsorbed on both Ni and Cu tnetals is sn!alL However, tl!e catcuhted vithte for the Fe complex is much Iess than tf!e esperit!tental v&e. As stated befow the magnitude of tf!e zr levei shift for tl!e &%C2H4 compkxes increases with ttte atomic number for both tf!e c&ttfation and experitnent. The Iaro,cdiscrepancy between the calcuIation and tt!e experiment for
Tke n!qnitudes (in eVf of the s-Ieve shifts it! U-C=& pk?.\es --!Lfetal
-19-88 -22.I4
__-
0.712 6.33 1 IO.855
tnetai atom 3d rtt~dIS orbirsls. It shouid be r!atcd tf!.tt
Table: 4
Free
I-
Fe CO
Ni cu
CZtlC-
E\p.
o-7
19
o-9 I.4 I.8
[lf
15 I21 I-9 iI1
can-
Volume
CHEWC-XL
66. numbr‘r j
the Fe-C,li, system seems to suggest th3t the geomctr!’ change of the C,i I1 molecule adsorbed on Fe metA is large. T.rbIe 3 shows that there exists 2 slight electron tmnsfer from the metal atom to the C,H2 lig~nd and the amount of the tmnsferred eitctrons decreases with the .ttomic number_ This result suggests that the metal 3d electrons of higher energy are more ntobik th&n those of lower energy. However. experiments on the work function change in CzHz adsorption h.tve shown th.rt the molecularly adsorbed C2H2 decreases the work function of Fe [3], Ni [ I] and Cu [2] met.ds, althoug!l the work function increase W.ISalso reported for the C2Hz adsorption on Fe surface f2] _Usuai:y t!te \vork function dccre.tse upon adsorption is interpreted tirdt an .tdsorbate has positive ch.trge_ The present result of the negativeiy charged C7H2 in the complexes confikts with the usual interpretation. The caIcuLtted results for the &I--C,H, complexes .trc shown in tables 5 Jnd 6. It is clear that the trend of these results is similar to that of the M-&HI _ The magnitude of the n-level (1 Bt,) shift in the hl-CzH3 is listed in table 7. AltbougI~ the calculated values are Luger than the e~peritnental values, the caIcuIation reproduces the csperimental trend. The very large ~Aue of 2.7 eV for the Cu comples arises from the fact that since the I BIu(rr) level energy of CJ Ha is much higher than the Cu 3d level energy as seenfrom the table I_ this level couples strongly with the 3d,a in .I bonding manner. The Cu 3d_a like Ievel couples strongly with the C2H4 IB,, Ieve in an sntibonding mmner. This effect appears also in the Ni-C,H, complexes to a less degree. Since the electron popuhttion results given in table 6 are simdsr to those of M-CZHZ given in table 3, similar discussions hold for M-C2H1. Table 5 Orbital energies (in eV) of JI-C2H4 Orbital ~-_____ ‘4,
IBt, 3Ag= 1Bzu 3B3u 2-A,
Tree -11
Fe
86
-14.70 -16.81 -18.51 -33 __ 71 _ -29.13
-12.70
-14.53 -16.68 -1856 -22-27 -29-40
co
-12.95
-14.89 -17.03 -18.88 -22.56 -29-80
Ni
-13.38 -15.06 -17.26 -19.07 -22.70 -30.03
CU
15 October 1979
PIIYSICS LIZ-l-l-ERS Table 6 Electron popuhtons of hI-CzH4 -- -- --_--.. ____. H C 11
I‘xc _
I-e __ -_. -
0.793 6.414 -
-._--
co
..--
0.797 6.505 8 802
0.806 6.520 7.734
-
Xi
CU
0.792 6.495 9.842
0.789 6.488 10 869
Table 7 The magntudes
(1x1eV) of the s;-ievd shifts in M-C~lI~
com-
pItA. ~______--_----
Metal
__-___.-
Te co &XI CU
CaIc____ ----0.8 l-1 1.5 2.7
E\P. 0.6 [I] 0.9 [31 1.0 [II
The calculated binding energies are unstable, that is, -0.3 eV to --_I 6 eV for the CZH2 complexes and -0.5 eV to - 1 .S eV for the C2H4 ones because the present calculation does not take into account electron correlation effects and no optimization of moIecuIar geometry is done [14-161.
4. Conclusion The present calculations expltin qualitatively the ir-level shift of C, Hz and C, H, in the UPS experiments of adsorption except Fe-C;H2 system. The n-level shift and the electron transfer from the metal atom to the ligand are related to the metal 3d level position_ if an rUPS experiment of adsorption on Co metal is done, it will be shown that the present picture is correct. Since the electron population results do not agree with the usual interpretation of the work function change in the adsorption experiment, more work is indicated on this problem.
-14 59
-15.20 -17.44 -19.16 -22.81_ -30.14
Acknowledgement This work ~3s done with support from the National Science Foundation Grant DMR-7723999.
533
Volume 66. number 3
CIE!WC.4L
PIIYSICS
References [I]
D-E- Eastman znd J E_ Demath. Japan. J. AppL Phys. Suppl. 2 (1971) 827. !3] K-Y_ Yu.W.E. Spicer. I. Lindau. P_ Phnetta and SF. Lm. Surfzce SCL 510976) I57_ [3j C. Brucket andT. Rhodin. J. Cad.47 (1977) 114. 141 If. Itoh. Japan. J. Appl. Phys’?i. IS (1976) 2311: 16 (1977)
2125_ [5j LE.Itoh. J. Phys- (Paris) SuppL c?, (1977) 23. 161 H. Itoh and A-B. Kunz, Z. Saturforsch_ 34, (1979)
1 II. Ph\s_ Letters 64 (1979)
[71 IL Itoh and A-6. Kum.Chem_ 5i6[S] Ii. itoh aa3 X-B- Eunz. to be submitted for pubIiczition_
15 October
LEl-IERS
1979
[9 j S- Topiol. J-W_ Moskowitz, CX. Melius. M.V. NW ton and J. I-affrr. ERDA Research and Drrelopmcnt Report (1976). [IO 1 B_ Roes. A. Vedlxd nnd G. Vmot, Theorer. Chim. .i\cta 20 (1971) 1. [I 11 B. Row snd P. Siwabahn. Theoret. Chim. L\cta I7 (1970) 209. [I21 L-F- Mattheiss,Ph~s. Rev_ I3-?A (1964) 191[ 13 f E_ Clementi and C. Roetti, At_ Dat.t NucL Data Tables 14 (1974) 177_ [ 14 1 W-C. Scope and 11 I-_ Schaeffer. Mol. Phyb. 34 (1977) 1037_ [ 151 T-H. Upton and WA_ Goddard III. J_ Am_ Chem. Sot. IO0 (1978) 3’1_ [ 16 1 H_ Bausch.M.D. Xerr ton and J_W_ Moskon itz. J. Chem. Ph) s. 69 (1978)
584.
PHYSICS LETTERS
MOLECULAR ORBITAL STUDY OF lNTERACTlONS SINGLE TRANSlTION 1IirqwI.i
ktreived
15 October
1979
OF
METAL ATOMS WITH C2H2 AND C2H4
ITOH .md A. Bmy KUNZ
22 June 1979: in tina farm 20 JuIy I979
Interactions of single transttion metal atoms of I-c. Co. Ni .md Cu u ith C2II2 and CzII4 were studied by an ab initio MO theor)-. The magnitudes of the HOMO IcwI shifts at-both Iigands increase with atomic number. The results were compared aith .xtiI.rbIe absorption experiments.
! _ Introduction
2. Method and model
The interaction of~etylene (C2Hz) and ethylene (C2HI) with transition metal surfaces has been estensively studied by me.ms of many experimental methods including photoeiectron spectroscopy [l-3] _ It is well known that one metal catalyst is effectike in some catalytic reaction but is lery poor in another reac-
Ab initio restricted Hartree-Fock MO calculatiqns were performed. Effective potentials replacing the Ar cores of the transition metal atoms were employed [9]Then, only the 3d, 4s and 4p valence orbitals for the metal atoms were taken into account. The 3d functions were taken from ref, [IO] and were incremented with one s function of exponent 020, one p function of exponent 025 and one d function of exponent 0.20. The gaussian basis set contracted to a minimal basis set was used for H and C atoms [ 1 l]_ The present basis sets gave good orbital energies and electron populations to the metal complexes reported before [6-S] _ The z-bonded mode!s for complexes were adoptedThe free moIecuiar geometries for C,H, (Dmh symmetry) and CzH4 (Dzh symmetry) in the complexes were assumed_ The distance between the metal atom (M) and the C atom was taken as 2.08 A for both C2H2 and C2Ha complexes_ The Z-antis was taken 3s the perpen-dicular direction to the C-C bond.
tion.
The difference
of adsorptive
and tzttalytic
proper-
ties of metals should be explained. The present authors [4.5] reported MO calculations on adsorption of hydrogen and CO on Ni 2nd Cu metal clusters which explained the difference of adsorptive properties of Ni and Cu in relation to the difference of their Sd-band positions and the simiktrity of their 4s4p bands. Moreover, the present authors [6-S] hake reported db initio MO calculations of the interactions of singe transition metal atoms of Fe, Co, Ni and Cu with PF,,CO, N, , NZH,, NaH4 and NH, ligands. As general trends. the &hest occupied molecular orbit& (HOMO’s) of these ligands shift toward lower energy_ The magnitudes of the shifts increase in the order of atomic number. The purpose of the present paper is to apply an ab initio MO theory to interactions of the single transition metal atoms of Fe, Co, Ni and Cu with C2H, and C2H1 ligands and to compare calculated results with available experimental results on adsorption_
3. Resuits and discussion Since the electron configurations of the transition metals with tz vaIence electrons [ 121 were assumed to be 3dn-14si, only the molecular states with highest spin multiplicities derived from the M 3d”-14s1 con531
_ _ f-11
St
___
0.733 6.539 9 $37
~;~ttr.ttitms acre rr.ttcufrtzsd itt tftc presctrr sttttif. It! tabfe I. :hc 3d and 4s orbktt energies of the rr~nsition t!!etal atoms with 3~P-~lst cot!figttr;ltiot!s wfiich were cAxthred by Clettrenti ztnd Koetti ii31 ztre listed. It is sees! ths ;~kfxw& she 4s orbital et!egies It-e neariy indepet!denr of atomic number, tf!c 3d orbitat et!ergics
ctrttreza rqidly in the order of .ttomic nut!!bcr_ The 3d orbMs xc rerv locaked sot!spared with tlte 4s orbit&_ TI!e large dift~rencc between the single metsI atoms and the real tnetds is rh;tt the 4s orbit& are tire hi$!est energy fevefs in the si&e 3toi!!s, whife the 4s bat& oftnetrrls sprc.tJ ztbotre;tnd bdorv the 3d brmds. Next the nkttktted results wifl be represented. Since is! the compIexes of ti!c m&d atotns with tl!e closed she11mokctdes considered in this paper tI!e free ~!!oIe&e-like orbitais retain their ftce n!olecular chsracter. the notation for the free molecules is used to rrpresent ekctrcmic states of rhe complexes_ Whet! the metf atoms interact with these molecules, both the 3d orbitalisand the 3s orbit& of the metaf atoms interact con. sidembly with the Ei~artdorbit& independent of figand species as observed as the reduction of the n!etai 3d bands in the photoefecrron experimenrs on adsorption. The vaience mofecttkr orbitaf energies and efectron pop&&ions of M-C&ii2 complexes are shown in tibles 2 and 3.. From tztbie 9, it is seen tI!at the C,H7 Iike revels shift from their free C2H2 ones due toti!: bondins interaction of the C2H, orbit& with the
Table 2 Orbiti erter@s (in eV) of Sf-CzH2 Fe
CO
Ni
Ctt
-i3.00
-1327 --I4_15
-1317 -1451
-1959 -2190
-I9=II -22x)0
-14.35 -14.39
-14.41 -&I?
-3529
-3025
-13.50
-19-a -21-75 -2958
532
-1999 -22.23
-35-49
-3055
_ _ _I~
Ltrge bot!dtt!g ttr!d rtt!tibot!dit!g it!ter.tcttot!s between f\\o orbit& occur whet! energy difkrct!ce of them is ~t!.t11nt!d whett ovcri.q> of tl!e IWU orbirals is large_ Titer!. the I iru I&e kvei xihicl! is tile f fOM0 of C, I-f2 shifts towards Iowver energy white the orher let,& rimA A itctr1~ the sztrtir~crtergtes as thi: free C2 f 11? _ Tf!e preseer resuhs are consistent with the UPS q&iill~t!fS.
Table 2 shows ti!at tI!e originally dqencrsted 1nu Ievefs spltc into two levels due to the interaction rviti! tffe t!!ettll atoms. Tlieir seprtmtions .tre sniclll t-or tile Co at!d Xi compie~s. The energy shifts of the aver,gc of the spfitred IckeIs frrtm tf!e free C2H2 is, feteis are shown in t.tble 4. The experimental v.ducs are sko shown in tabIe 4. TI!e tnagnitude of the c&xtI.tted shift increases ix! tl!e order of atomic t!utnber because the met& atom 3d orbirrti energy decreases with the aton!ic number as seen from table f _ Tile calculated vrthtes for rhe Ki and Cu con!pIexes are in good agreement with the experiments. sttggestit!g that the geometry change of tile C,H, - _ tnofecule adsorbed on both Ni and Cu tnetals is sn!alL However, tl!e catcuhted vithte for the Fe complex is much Iess than tf!e esperit!tental v&e. As stated befow the magnitude of tf!e zr levei shift for tl!e &%C2H4 compkxes increases with ttte atomic number for both tf!e c&ttfation and experitnent. The Iaro,cdiscrepancy between the calcuIation and tt!e experiment for
Tke n!qnitudes (in eVf of the s-Ieve shifts it! U-C=& pk?.\es --!Lfetal
-19-88 -22.I4
__-
0.712 6.33 1 IO.855
tnetai atom 3d rtt~dIS orbirsls. It shouid be r!atcd tf!.tt
Table: 4
Free
I-
Fe CO
Ni cu
CZtlC-
E\p.
o-7
19
o-9 I.4 I.8
[lf
15 I21 I-9 iI1
can-
Volume
CHEWC-XL
66. numbr‘r j
the Fe-C,li, system seems to suggest th3t the geomctr!’ change of the C,i I1 molecule adsorbed on Fe metA is large. T.rbIe 3 shows that there exists 2 slight electron tmnsfer from the metal atom to the C,H2 lig~nd and the amount of the tmnsferred eitctrons decreases with the .ttomic number_ This result suggests that the metal 3d electrons of higher energy are more ntobik th&n those of lower energy. However. experiments on the work function change in CzHz adsorption h.tve shown th.rt the molecularly adsorbed C2H2 decreases the work function of Fe [3], Ni [ I] and Cu [2] met.ds, althoug!l the work function increase W.ISalso reported for the C2Hz adsorption on Fe surface f2] _Usuai:y t!te \vork function dccre.tse upon adsorption is interpreted tirdt an .tdsorbate has positive ch.trge_ The present result of the negativeiy charged C7H2 in the complexes confikts with the usual interpretation. The caIcuLtted results for the &I--C,H, complexes .trc shown in tables 5 Jnd 6. It is clear that the trend of these results is similar to that of the M-&HI _ The magnitude of the n-level (1 Bt,) shift in the hl-CzH3 is listed in table 7. AltbougI~ the calculated values are Luger than the e~peritnental values, the caIcuIation reproduces the csperimental trend. The very large ~Aue of 2.7 eV for the Cu comples arises from the fact that since the I BIu(rr) level energy of CJ Ha is much higher than the Cu 3d level energy as seenfrom the table I_ this level couples strongly with the 3d,a in .I bonding manner. The Cu 3d_a like Ievel couples strongly with the C2H4 IB,, Ieve in an sntibonding mmner. This effect appears also in the Ni-C,H, complexes to a less degree. Since the electron popuhttion results given in table 6 are simdsr to those of M-CZHZ given in table 3, similar discussions hold for M-C2H1. Table 5 Orbital energies (in eV) of JI-C2H4 Orbital ~-_____ ‘4,
IBt, 3Ag= 1Bzu 3B3u 2-A,
Tree -11
Fe
86
-14.70 -16.81 -18.51 -33 __ 71 _ -29.13
-12.70
-14.53 -16.68 -1856 -22-27 -29-40
co
-12.95
-14.89 -17.03 -18.88 -22.56 -29-80
Ni
-13.38 -15.06 -17.26 -19.07 -22.70 -30.03
CU
15 October 1979
PIIYSICS LIZ-l-l-ERS Table 6 Electron popuhtons of hI-CzH4 -- -- --_--.. ____. H C 11
I‘xc _
I-e __ -_. -
0.793 6.414 -
-._--
co
..--
0.797 6.505 8 802
0.806 6.520 7.734
-
Xi
CU
0.792 6.495 9.842
0.789 6.488 10 869
Table 7 The magntudes
(1x1eV) of the s;-ievd shifts in M-C~lI~
com-
pItA. ~______--_----
Metal
__-___.-
Te co &XI CU
CaIc____ ----0.8 l-1 1.5 2.7
E\P. 0.6 [I] 0.9 [31 1.0 [II
The calculated binding energies are unstable, that is, -0.3 eV to --_I 6 eV for the CZH2 complexes and -0.5 eV to - 1 .S eV for the C2H4 ones because the present calculation does not take into account electron correlation effects and no optimization of moIecuIar geometry is done [14-161.
4. Conclusion The present calculations expltin qualitatively the ir-level shift of C, Hz and C, H, in the UPS experiments of adsorption except Fe-C;H2 system. The n-level shift and the electron transfer from the metal atom to the ligand are related to the metal 3d level position_ if an rUPS experiment of adsorption on Co metal is done, it will be shown that the present picture is correct. Since the electron population results do not agree with the usual interpretation of the work function change in the adsorption experiment, more work is indicated on this problem.
-14 59
-15.20 -17.44 -19.16 -22.81_ -30.14
Acknowledgement This work ~3s done with support from the National Science Foundation Grant DMR-7723999.
533
Volume 66. number 3
CIE!WC.4L
PIIYSICS
References [I]
D-E- Eastman znd J E_ Demath. Japan. J. AppL Phys. Suppl. 2 (1971) 827. !3] K-Y_ Yu.W.E. Spicer. I. Lindau. P_ Phnetta and SF. Lm. Surfzce SCL 510976) I57_ [3j C. Brucket andT. Rhodin. J. Cad.47 (1977) 114. 141 If. Itoh. Japan. J. Appl. Phys’?i. IS (1976) 2311: 16 (1977)
2125_ [5j LE.Itoh. J. Phys- (Paris) SuppL c?, (1977) 23. 161 H. Itoh and A-B. Kunz, Z. Saturforsch_ 34, (1979)
1 II. Ph\s_ Letters 64 (1979)
[71 IL Itoh and A-6. Kum.Chem_ 5i6[S] Ii. itoh aa3 X-B- Eunz. to be submitted for pubIiczition_
15 October
LEl-IERS
1979
[9 j S- Topiol. J-W_ Moskowitz, CX. Melius. M.V. NW ton and J. I-affrr. ERDA Research and Drrelopmcnt Report (1976). [IO 1 B_ Roes. A. Vedlxd nnd G. Vmot, Theorer. Chim. .i\cta 20 (1971) 1. [I 11 B. Row snd P. Siwabahn. Theoret. Chim. L\cta I7 (1970) 209. [I21 L-F- Mattheiss,Ph~s. Rev_ I3-?A (1964) 191[ 13 f E_ Clementi and C. Roetti, At_ Dat.t NucL Data Tables 14 (1974) 177_ [ 14 1 W-C. Scope and 11 I-_ Schaeffer. Mol. Phyb. 34 (1977) 1037_ [ 151 T-H. Upton and WA_ Goddard III. J_ Am_ Chem. Sot. IO0 (1978) 3’1_ [ 16 1 H_ Bausch.M.D. Xerr ton and J_W_ Moskon itz. J. Chem. Ph) s. 69 (1978)
584.