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Photoelectron spectroscopic study of hydrogen peroxide
Volume
2.5; number
1
1 March 1974
CHEMICAL PHYSICS LE-I-IERS
_-
PHOTQELECTRONSPECTROSCOPICSTUDYOFHYDROGENPliROXIDE Kazuteru OSAFUNE
and Katsumi K.IMURA*
Physical Ciwnzisrp Laboratory, Institute of Applied h’lectricity, Hokkcido Uni~~ersit_v. Sapporo 060. Japan
Received 3 December 1973
The He I photoelectron spectrum of hydrogen peroside
is reported, showing a splitting of 1.0 eV between the first two bands due to the oxygen noxbonding orbit&. The present CNDO/I calculations on hydrogen peroxide indicate that the nonbonding orbital splitting as well as the orbital assignment depend largely upon the dihedral angle between the two haIves of the molecule. The photoelectron bands may be assigned to the 4b{n_(O! ),5a{n+(O)). 4a{u(O-0)). 3a(u+(O-H)) and 3b(o_(O-H)}, orbit& in this order. where the + and - combinations indicate symmetric and antisymmetric combinations with resnect to the CT asis. The above orbital assignments are supported by a consideration of a sum rule concerning vertical ionization energies.
1. Introduction
Hydrogen peroxide and hydrazine are typical molecuIes which have skew ground state conformations (C-J In our previous photoelectron study of hydrazine [I ] , it was indicated that the sphtting between the photoelectron bands due to the nitrogen nonbonding orbitals largely depends upon the dihedral angle in the skew conformation, and the splitting between the two nonbonding bands may be interpreted in terms of possible dihedral angles, through semi-empirical calcula- . tions. Recently, interactions between two equivalent lone pair orbitals in various organic compounds with hetero atoms have been studied by photoelectron spectroscopy by several authors [2-61. For hydrogen peroxide, an infrared study by Hunt et al. [7] has given a value of 11 lo 30’ for the dihedral angle..The electronic structure of hydrogen peroxide has received much attention by many theoretical chemists [S, Q] mainly in relation to the rotational barrier in the skew conf&mation. However, no photoelectron
studies of hydrogen peroxide have been published so far. Some experimental data on the first ionizatiori po-.tential of hydrogen p&oxide were obtained earlier ’ from electron impact studies by Robertson (12.1. f . 0.3 ev) [ 10 ] , by Lindeman and Guffy (1 I 26 + 0.05
-_
:
eV) [ 1 I], and by Foner and Hudson (10.92 + 0.05 eV) [ 12]_ each one in disagreement with one another. Under these circumstances we have considered it interesting
to obtain
information
on the skew
confor-
as well as on the valence orbital structure of hydrogen peroxide by means of photoelectron spectroscopy with the helium 584 & line, using CND0/‘2 calculations and a consideration of a sum rile on vertical ionization energies described in our previous papers [l, 13,141. mation
2. Experimekal Hydrogen peroxide was obtained by subsequent pu-
rification from a commercial 50% solution in three stages [ 151: (1) fractional distillation at about 60°C under reduced pressure; (2) separation of pure hydrogen peroxide from this concentrated sqlution by fractional crystallization; (3)‘further distillation in vacuum to rem&e more volatile im$u&ies. Gaseous hydrogen peroxide was intioduced t?~rough a vacuum glass-line : with a t&on needle valve. No metal tube w+s$hed to -’ ..-. avoid decomposition. I. Measutem&it$ of the He .I phdthelectron spe&ai&& ; carried.odt with-a Ja& PE h&&resolution photdkec- : ,” tron SpecGo&eter,used priT&ly. 11;. 131. @ib&ign.: .; : .:,-: ..L _ .,.. : 1’::;lj‘l:..: : _: ,-.. /..-: ._ .: ,’ :. I :’ -I ., : ,,.. : i -. __._: ..“.
CHEMICAL PHYSICS LETTERS
Volume 25. number 1 of the ionization known ionization
3.
1 hbrch 1974 CZW
ener,9 scale was carried out using energy values of Xe as a standard.
I
c,
CZH
r
1
Theoretical calculations Orbital
energies
of hydrogen
peroxide
were calcu-
lated by the CND0/2 method [16] at dihedral angles (4) from 0” (cis) to 180” (rra:rs) at intervals of IO”. Structure parameters used in the present calculations were taken from the literature [ 171; r(O-0) = 1.475 a; r(O-H) = 0.950 A and LOOH = 94” 48’. The calculations were carried out with a Facosn-230/60 computer at the Computing Center of Hokkaido University.
4. Results and discussion
The He I photoelectron spectrum of hydrogen peroxide in the range below 20 eV is shown in fig. 1, in which vertical lines indicate the location of the vertical ionization energies obtained here and summarised
in table 1. The orbital energies obtained from the calculations are plotted against (bin fig. 2. the resulting orbital types and symmetries being aIso indiCNDO/Z
cated.
The first two broad bands appear with maxima at 12.69 eV in fig. 1, with a splitting of i .O eV, ItIdy be assigned to the - and + combinations, respectively, of the oxygen nonbonding orbit&, n,(O). on the basis of the CNDO/2 calculations. It should be noted that the two highest orbital-energy curves in fig. 11.69‘and
x _ 2 P
cc 0
-
-m-
1
0
45
DIHEDRAL
t 90
135
ml
ANGLE (deg)
Fig. 2. Results of CNDO/2 calculations. (Each value was reduced by 4 eV.) 2 cross each other at about 90” and therefore the splitting of the two nonbonding bands is closely associated with the dihedral angIe. The third photoelectron band at 15.33 eV is cIearly separated as a single band, ascribed mainly to tfle O-O o orbital whose energy is almost independent of the dihedral angle, as can be seen from fig. 2. According to the CNDO/‘! calculations, the third orbital is approximately pure 0(0-O), while the n(0) orbitals mix to a considerable extent with the o(O-H) orbitais. This may be supported by the fact that the third band is relatively sharp. The fourth band appears with its maximum at 17.4 eV, with which the fifth band may be considered to overlap, since the area under the curve in the 16-20 eV region is approximately twice that of the third band. The 17.4 eV bands correspond to the + and - combinations of the O-H u orbitals. It should also be mentioned that the a,(O-1-1) bands are close to the methanol a(O-H) band appearing at 17.5 eV [141_ Slight peaks appearing at 12.6 and 18.2 eV in fig. 1 are due to traces of water and oxygen, respectively, produced by decomposition from hydrogen peroxide. The photoelectron spectra measured before and after process (3) in our sample purification were compared, and it was found that the impurity peaks in the latter case are much weaker in intensity than tflose in the
former case.
d
+
12
10 Fig.
48
1z lONlZAllON
I. Photoelectron
16 ENERGY (rV
18 )
specrrum of hydrogen peroxide.
20
As seen from fig. 2, the highest occupied orbital of hydrogen peroxide with symmetry C, belongs to species b in the 90- 180“ region, but species a in the O90” region. From the present CNDOM calculations the 1 .O eV splitting of the nonbonding orbitals was reproduced at d values of 50 and 1X0. The latter value (125’)
1 March 1974
CHEMICAL PHYSICS LETTERS
Volume 25. number 1
Table 1 Experimental
vertical ionization
energies and calculated
Experimental vertical
Calculated orbital enegy and character
ionization
by CND0/2
energy
by sum rule
(at (6 = 11 I” 30”)
11.69(1,)
-12.83
4b{n_(O))
b
-13.41
Sa{n+(O)}
a
IS.33 Us)
-14.81
4a{oo(O-O)]
3
(14)
-18.03
3a{o+(O-HI)
a
-1 R.97
3b {o-(0-H))
b
17.40 (15)
value (I 1 I” 30’) derived from infrared spectra [7] _Therefore, we may conclude that the orbital ordering of hydrogen peroxide is 3b, 3a, 4a, Sa and 4b. This result is different from that of hydrazine (3a, 3b, 4a, 4b, 5a), previously reported in ref. [ 1 ] _The differences in orbital symmetries between hydrogen peroxide and hydrazine arise from the difference in the relative orientation of the nonbonding orbitals with respect to the C, axis. The total orbital energy was also calculatedby the CNDO/2 method. However, it gave an energy minimum at $J= 180” in disagreement with the experimental skew conformation_ It has been found that such calculations made to obtain the position of the minimum of total orbital energy does not always give a correct dihedral angle. However, the argument about the splitting of the nonbonding orbitals mentioned above provides valuable information concerning the dihedral angle. A similar situation has also occurred in the case of hydrazine as previously pointed out [l] . The orbital energies calculated here with # = 11 la 30’ reported by Hunt et al. [7] are compared with experiment in table 1, together with the orbital types and symmetries.
bitals. The empirical values used in those works 113,
4.2. Sum rule
= 12.61 5lCO) fo(o_o,
= 16.10
Recent photoelectron studies of various alkyl compounds by Kimura et al. [ 13,141 have suggested that the sum rule holds for vertical ionization energies to a considerable extent. For each of the compounds, a total sum of experimental vertical ionization energies below about 18 eV is well reproduced by a summation of the empirical values over all the p-type Iocalized or-
fo(O_H)
= 16.60
is fairly close to the available experimental
....
.: ‘.
Orbital symmetry
12.69 (1-i.) 17.40
-:
orbital energies (in eW for hydrogen peroside
‘. 1
.,..
,..I
-._._., :
:..
_‘J’.. -.,_
_I.,
__. -..
.-
:. .~
I41 are based on the vertical ionization energies of simpIe related compounds. For hydrogen peroxide, we take five p-type localized orbitals into account, which are two n(O), ~(0-0) and two o(O-H) orbitals, and employ the empirical ionization ener,v values shown in table 2, where the value for
n(0) is taken from the first vertical of water [ 1S] and that for o(O-H) ue of the second and third vertical of water [!8j . The empirical value
ionization energy from the mean valionization energies for 0(0-o) was
estimated so as to reproduce the experimental total sum (II + I7 + I3 + I4 + I, = 74.5 eV). As seen in table
2, good agriement is obtained between the experimental and calculated partial sums in the b species, suggesting that the highest orbital belongs to the b species, not the a, supporting the CNDO/?; results described previously. Table 2 Ionization energy values estimated for the localized orbit& and the comparison of the partial sums of the experimental and calculated ionization energiesfor hydrogen peroxide (in ev)
species b specks
a
expti.
( calcd.
II
+I4
=
29.09
In +foco_Hj
= 29.21
1, t I, + (15) = 45.47 In +Im(o_o)
+ZO(O_Hj
= 45.31
Volume 25. number 1
CHEMICAL PHYSICS LETTERS
References
1 March 1974
[ 101 A.J.B. Robertson, Trans. Faraday Sot. 48 (1952) 228.
[ I1 ] L.P. Lindeman and J.C. Guffy, 3. Chem. Phys. 29 (1958) [ 11 K. Osafune, S. Katsumata and K. Kimura, Chem. Phys. Lrtters 19 (1973) 369. [ZI E. Heilbronner and K.A. Mustkat, J. Am. Chem. SOC. 92 (1970) 3818; P. Gleiter, E. Heilbronner and V. Hornung, Helv. Chim. Acta 55 (1972) 255. I31 D.A. Sweigart and D.W. Turner, J. Am. Chem. Sot. 94 (1972) 5599. 141 T. Kobayashi and S. Nagakura. Bull. Chem. Sot. Japan 46 (1973)
1558.
[Sl P. Rademacher, Angew. Chem. Intern. Ed. 12 (1973) 408. (6f S.F. Nelsen and J.M. Buschek, J. Am, Chem. Sot. 95 (1973) 2011; S.F. NeJsen. J.hI. Buschek and P.J. Hintz, J. Am. Chem. sot. 95 (1973) 2012. 171 R-H. Hunt, R-A. Lcacock, C.W. Peters and K.T. Hecht, J. Chem. Phys. 42 (1965) 1931. [8] A. Veillard, Theoret. Chim. Acta 18 0970) 21, and mferences therein.
191H. Yamabe, H. Kato and T. Yonezawa, Bull. Chem. Sot. Japan 44(1971) 22.
247. [ 121 S.N- Foster and R-L. Hudson, J. Chem. Phys. 36 (1962) 2676. I131 K. Kimura. S. J&tsumata. Y. Achiba. H. hJatsnmoto and S. Nagakura, Bull. Chem. Sot. Japan 46 (1973) 373: S. ffitsumata and K. Kimura, Bull. Chem. Sot. Japan 46 (1973) 1342; T. Yamazaki. S. Katsumata and K. Kiura, J. Electron Spectra- 1 (1973). to be published. S. Katsumata. ‘f. Jwai and K. Kimura. Buil. Chem. Sot. Japan 46 (1973) 3391. 0. Msassand W.H. Hatcher, J. Am. Chem. Sot. 42 (1920) 2548. MS. Gordon and J-A. Pople. J. Chem. Phys. 49 (1968) 4643. [ 171 R.L Redington, W.B. Olson and P.C. Cross, J. Chem. Phys. 36 (1962) 1311. [181 D-W. ‘limer,C. Baker, A.D. Baker and CR. Brundle, hfolecular photoelectron
1969).
spectroscopy
(\ViIey, New York,
2.5; number
1
1 March 1974
CHEMICAL PHYSICS LE-I-IERS
_-
PHOTQELECTRONSPECTROSCOPICSTUDYOFHYDROGENPliROXIDE Kazuteru OSAFUNE
and Katsumi K.IMURA*
Physical Ciwnzisrp Laboratory, Institute of Applied h’lectricity, Hokkcido Uni~~ersit_v. Sapporo 060. Japan
Received 3 December 1973
The He I photoelectron spectrum of hydrogen peroside
is reported, showing a splitting of 1.0 eV between the first two bands due to the oxygen noxbonding orbit&. The present CNDO/I calculations on hydrogen peroxide indicate that the nonbonding orbital splitting as well as the orbital assignment depend largely upon the dihedral angle between the two haIves of the molecule. The photoelectron bands may be assigned to the 4b{n_(O! ),5a{n+(O)). 4a{u(O-0)). 3a(u+(O-H)) and 3b(o_(O-H)}, orbit& in this order. where the + and - combinations indicate symmetric and antisymmetric combinations with resnect to the CT asis. The above orbital assignments are supported by a consideration of a sum rule concerning vertical ionization energies.
1. Introduction
Hydrogen peroxide and hydrazine are typical molecuIes which have skew ground state conformations (C-J In our previous photoelectron study of hydrazine [I ] , it was indicated that the sphtting between the photoelectron bands due to the nitrogen nonbonding orbitals largely depends upon the dihedral angle in the skew conformation, and the splitting between the two nonbonding bands may be interpreted in terms of possible dihedral angles, through semi-empirical calcula- . tions. Recently, interactions between two equivalent lone pair orbitals in various organic compounds with hetero atoms have been studied by photoelectron spectroscopy by several authors [2-61. For hydrogen peroxide, an infrared study by Hunt et al. [7] has given a value of 11 lo 30’ for the dihedral angle..The electronic structure of hydrogen peroxide has received much attention by many theoretical chemists [S, Q] mainly in relation to the rotational barrier in the skew conf&mation. However, no photoelectron
studies of hydrogen peroxide have been published so far. Some experimental data on the first ionizatiori po-.tential of hydrogen p&oxide were obtained earlier ’ from electron impact studies by Robertson (12.1. f . 0.3 ev) [ 10 ] , by Lindeman and Guffy (1 I 26 + 0.05
-_
:
eV) [ 1 I], and by Foner and Hudson (10.92 + 0.05 eV) [ 12]_ each one in disagreement with one another. Under these circumstances we have considered it interesting
to obtain
information
on the skew
confor-
as well as on the valence orbital structure of hydrogen peroxide by means of photoelectron spectroscopy with the helium 584 & line, using CND0/‘2 calculations and a consideration of a sum rile on vertical ionization energies described in our previous papers [l, 13,141. mation
2. Experimekal Hydrogen peroxide was obtained by subsequent pu-
rification from a commercial 50% solution in three stages [ 151: (1) fractional distillation at about 60°C under reduced pressure; (2) separation of pure hydrogen peroxide from this concentrated sqlution by fractional crystallization; (3)‘further distillation in vacuum to rem&e more volatile im$u&ies. Gaseous hydrogen peroxide was intioduced t?~rough a vacuum glass-line : with a t&on needle valve. No metal tube w+s$hed to -’ ..-. avoid decomposition. I. Measutem&it$ of the He .I phdthelectron spe&ai&& ; carried.odt with-a Ja& PE h&&resolution photdkec- : ,” tron SpecGo&eter,used priT&ly. 11;. 131. @ib&ign.: .; : .:,-: ..L _ .,.. : 1’::;lj‘l:..: : _: ,-.. /..-: ._ .: ,’ :. I :’ -I ., : ,,.. : i -. __._: ..“.
CHEMICAL PHYSICS LETTERS
Volume 25. number 1 of the ionization known ionization
3.
1 hbrch 1974 CZW
ener,9 scale was carried out using energy values of Xe as a standard.
I
c,
CZH
r
1
Theoretical calculations Orbital
energies
of hydrogen
peroxide
were calcu-
lated by the CND0/2 method [16] at dihedral angles (4) from 0” (cis) to 180” (rra:rs) at intervals of IO”. Structure parameters used in the present calculations were taken from the literature [ 171; r(O-0) = 1.475 a; r(O-H) = 0.950 A and LOOH = 94” 48’. The calculations were carried out with a Facosn-230/60 computer at the Computing Center of Hokkaido University.
4. Results and discussion
The He I photoelectron spectrum of hydrogen peroxide in the range below 20 eV is shown in fig. 1, in which vertical lines indicate the location of the vertical ionization energies obtained here and summarised
in table 1. The orbital energies obtained from the calculations are plotted against (bin fig. 2. the resulting orbital types and symmetries being aIso indiCNDO/Z
cated.
The first two broad bands appear with maxima at 12.69 eV in fig. 1, with a splitting of i .O eV, ItIdy be assigned to the - and + combinations, respectively, of the oxygen nonbonding orbit&, n,(O). on the basis of the CNDO/2 calculations. It should be noted that the two highest orbital-energy curves in fig. 11.69‘and
x _ 2 P
cc 0
-
-m-
1
0
45
DIHEDRAL
t 90
135
ml
ANGLE (deg)
Fig. 2. Results of CNDO/2 calculations. (Each value was reduced by 4 eV.) 2 cross each other at about 90” and therefore the splitting of the two nonbonding bands is closely associated with the dihedral angIe. The third photoelectron band at 15.33 eV is cIearly separated as a single band, ascribed mainly to tfle O-O o orbital whose energy is almost independent of the dihedral angle, as can be seen from fig. 2. According to the CNDO/‘! calculations, the third orbital is approximately pure 0(0-O), while the n(0) orbitals mix to a considerable extent with the o(O-H) orbitais. This may be supported by the fact that the third band is relatively sharp. The fourth band appears with its maximum at 17.4 eV, with which the fifth band may be considered to overlap, since the area under the curve in the 16-20 eV region is approximately twice that of the third band. The 17.4 eV bands correspond to the + and - combinations of the O-H u orbitals. It should also be mentioned that the a,(O-1-1) bands are close to the methanol a(O-H) band appearing at 17.5 eV [141_ Slight peaks appearing at 12.6 and 18.2 eV in fig. 1 are due to traces of water and oxygen, respectively, produced by decomposition from hydrogen peroxide. The photoelectron spectra measured before and after process (3) in our sample purification were compared, and it was found that the impurity peaks in the latter case are much weaker in intensity than tflose in the
former case.
d
+
12
10 Fig.
48
1z lONlZAllON
I. Photoelectron
16 ENERGY (rV
18 )
specrrum of hydrogen peroxide.
20
As seen from fig. 2, the highest occupied orbital of hydrogen peroxide with symmetry C, belongs to species b in the 90- 180“ region, but species a in the O90” region. From the present CNDOM calculations the 1 .O eV splitting of the nonbonding orbitals was reproduced at d values of 50 and 1X0. The latter value (125’)
1 March 1974
CHEMICAL PHYSICS LETTERS
Volume 25. number 1
Table 1 Experimental
vertical ionization
energies and calculated
Experimental vertical
Calculated orbital enegy and character
ionization
by CND0/2
energy
by sum rule
(at (6 = 11 I” 30”)
11.69(1,)
-12.83
4b{n_(O))
b
-13.41
Sa{n+(O)}
a
IS.33 Us)
-14.81
4a{oo(O-O)]
3
(14)
-18.03
3a{o+(O-HI)
a
-1 R.97
3b {o-(0-H))
b
17.40 (15)
value (I 1 I” 30’) derived from infrared spectra [7] _Therefore, we may conclude that the orbital ordering of hydrogen peroxide is 3b, 3a, 4a, Sa and 4b. This result is different from that of hydrazine (3a, 3b, 4a, 4b, 5a), previously reported in ref. [ 1 ] _The differences in orbital symmetries between hydrogen peroxide and hydrazine arise from the difference in the relative orientation of the nonbonding orbitals with respect to the C, axis. The total orbital energy was also calculatedby the CNDO/2 method. However, it gave an energy minimum at $J= 180” in disagreement with the experimental skew conformation_ It has been found that such calculations made to obtain the position of the minimum of total orbital energy does not always give a correct dihedral angle. However, the argument about the splitting of the nonbonding orbitals mentioned above provides valuable information concerning the dihedral angle. A similar situation has also occurred in the case of hydrazine as previously pointed out [l] . The orbital energies calculated here with # = 11 la 30’ reported by Hunt et al. [7] are compared with experiment in table 1, together with the orbital types and symmetries.
bitals. The empirical values used in those works 113,
4.2. Sum rule
= 12.61 5lCO) fo(o_o,
= 16.10
Recent photoelectron studies of various alkyl compounds by Kimura et al. [ 13,141 have suggested that the sum rule holds for vertical ionization energies to a considerable extent. For each of the compounds, a total sum of experimental vertical ionization energies below about 18 eV is well reproduced by a summation of the empirical values over all the p-type Iocalized or-
fo(O_H)
= 16.60
is fairly close to the available experimental
....
.: ‘.
Orbital symmetry
12.69 (1-i.) 17.40
-:
orbital energies (in eW for hydrogen peroside
‘. 1
.,..
,..I
-._._., :
:..
_‘J’.. -.,_
_I.,
__. -..
.-
:. .~
I41 are based on the vertical ionization energies of simpIe related compounds. For hydrogen peroxide, we take five p-type localized orbitals into account, which are two n(O), ~(0-0) and two o(O-H) orbitals, and employ the empirical ionization ener,v values shown in table 2, where the value for
n(0) is taken from the first vertical of water [ 1S] and that for o(O-H) ue of the second and third vertical of water [!8j . The empirical value
ionization energy from the mean valionization energies for 0(0-o) was
estimated so as to reproduce the experimental total sum (II + I7 + I3 + I4 + I, = 74.5 eV). As seen in table
2, good agriement is obtained between the experimental and calculated partial sums in the b species, suggesting that the highest orbital belongs to the b species, not the a, supporting the CNDO/?; results described previously. Table 2 Ionization energy values estimated for the localized orbit& and the comparison of the partial sums of the experimental and calculated ionization energiesfor hydrogen peroxide (in ev)
species b specks
a
expti.
( calcd.
II
+I4
=
29.09
In +foco_Hj
= 29.21
1, t I, + (15) = 45.47 In +Im(o_o)
+ZO(O_Hj
= 45.31
Volume 25. number 1
CHEMICAL PHYSICS LETTERS
References
1 March 1974
[ 101 A.J.B. Robertson, Trans. Faraday Sot. 48 (1952) 228.
[ I1 ] L.P. Lindeman and J.C. Guffy, 3. Chem. Phys. 29 (1958) [ 11 K. Osafune, S. Katsumata and K. Kimura, Chem. Phys. Lrtters 19 (1973) 369. [ZI E. Heilbronner and K.A. Mustkat, J. Am. Chem. SOC. 92 (1970) 3818; P. Gleiter, E. Heilbronner and V. Hornung, Helv. Chim. Acta 55 (1972) 255. I31 D.A. Sweigart and D.W. Turner, J. Am. Chem. Sot. 94 (1972) 5599. 141 T. Kobayashi and S. Nagakura. Bull. Chem. Sot. Japan 46 (1973)
1558.
[Sl P. Rademacher, Angew. Chem. Intern. Ed. 12 (1973) 408. (6f S.F. Nelsen and J.M. Buschek, J. Am, Chem. Sot. 95 (1973) 2011; S.F. NeJsen. J.hI. Buschek and P.J. Hintz, J. Am. Chem. sot. 95 (1973) 2012. 171 R-H. Hunt, R-A. Lcacock, C.W. Peters and K.T. Hecht, J. Chem. Phys. 42 (1965) 1931. [8] A. Veillard, Theoret. Chim. Acta 18 0970) 21, and mferences therein.
191H. Yamabe, H. Kato and T. Yonezawa, Bull. Chem. Sot. Japan 44(1971) 22.
247. [ 121 S.N- Foster and R-L. Hudson, J. Chem. Phys. 36 (1962) 2676. I131 K. Kimura. S. J&tsumata. Y. Achiba. H. hJatsnmoto and S. Nagakura, Bull. Chem. Sot. Japan 46 (1973) 373: S. ffitsumata and K. Kimura, Bull. Chem. Sot. Japan 46 (1973) 1342; T. Yamazaki. S. Katsumata and K. Kiura, J. Electron Spectra- 1 (1973). to be published. S. Katsumata. ‘f. Jwai and K. Kimura. Buil. Chem. Sot. Japan 46 (1973) 3391. 0. Msassand W.H. Hatcher, J. Am. Chem. Sot. 42 (1920) 2548. MS. Gordon and J-A. Pople. J. Chem. Phys. 49 (1968) 4643. [ 171 R.L Redington, W.B. Olson and P.C. Cross, J. Chem. Phys. 36 (1962) 1311. [181 D-W. ‘limer,C. Baker, A.D. Baker and CR. Brundle, hfolecular photoelectron
1969).
spectroscopy
(\ViIey, New York,