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The Ionezation Potentials of BF3, BC13 and BBr3
THE 1ONIZATION Department
POTENTIALS
OF BPS, BC+
Ft.J. BOYD * and D. C. FBOST of Chemistr,, University of B. C., Vancouver 8, B.C., Received
1 March
AND BBr3 Canada
1968
The ionization potentials of BF3. BC13 and BBr3 have been found by photoelectron spectrometry, compared with those cakulated using an s and p electron semi-empirical SCF treatment.
We wish to present new values for the ionization potentials (IP’s) of BF3, BCl3 and BBr3 obtained by the photoelectron kinetic energy analysis
(PEKE)
technique
[l]
calculations include s and p orbitals orIy in the basis set and therefore may not be as satisfactory for BC13, BBr3 and BI3 as for BF3, depending on the extent to which d orbitals are invoLved in the first three. The PEEE first IP’s are in serious disagreement with the electron impact values (except for Law and Margrave’s IP for BCl3), however the PEKE values are strongly preferred. ELectron impact IP’s have been found to be in error before [6]. Assuming the e’ and e” orbitals to remain doubly degenerate, and the inner shell IF’s to lie above 20 eV, then six IP’s might be expected from our experiments (see Walsh [7f). The spectra give the expected number for BC13, but onLy five each for the other two. This may be due to instrumental inadequacy as far as resoLution is concerned (we are normally able to distinguish between states separated by 0.1 eV, however for these molecules there are indications of vibrational structure on many of the electronic bands and this may cause iI? masking).
and by calculations
using an all-valence-electron semi-empirical SCF treatment. Electron impact studies [2,3] on these molecules have yielded the first IP only, moreover where data from two laboratories can be compared (in the case of BC13) the agreement is poor. Armstrong and Perkins [4] have studied the ground state properties of the boron trihalides by the Pariser-Parr-Pople SCF method. They considered B electrons only, and they compared their calculated IP’s with the electron impact results mentioned above. The method of Sichel and Whitehead [ 51, which includes all valence electrons and predicts both z and 0 IP’s, has now been applied to these molecules, and the results are given in tables 1 and 2 with the symmetry designation of the MO’s and their classification symmetric or antisymmetric to the molecular plane (u or v). It should be mentioned that the
First
Ip’s
Table 1 of the boron trihalides
Electron impact BF3
15.5 (2)
BC13
10.9 (3).
BBr3
9.7 (3)
BI3
9.1 (3)
* Present address: Chemistry Department, University, Montreal, Canada. April
1968
PEKE (vertical IP)
12.0 (2)
and
(in eV) Theoretical
A and P [S]
15.95
160,
11.97
12.2. ir
12.68. 0
10.72
11.2, ii
11.47, o-
10.2, 7T
11.03, ff
McGill
649
7?
This work 16.05, 0
R. J. BOYD
650 Table 2 Tp’s of the boron trihalides (in eV)
PEKE (vert.) 15.95
BC13 BBr BF3 Calc. Calc. PEKE PEKE 8 ! ** this work (vert.) this work (vert.) thisazork 16_05,e’,o
16.65 16.69&o
11.97
12.68,e’.o
12.43 13.35&o
10.72
11.47,e’XJ
enco;lragement, and their colleagues for stimulating discussions. The permission of Drs. J. M. Sichel and M. A. Whitehead to use their method is gratefully acknowledged.
References
11.26 12.04&J
17.21 16.74.e”,n 12.77 13.50.e”,n 11.77 12.25.e”,lr 17_PS,e’.Q 14.50 14.74,$,~
and D. C. FROST
13.14 13.46,aG.n
19.0
17.90&.n
15.75 14.37,e’,U
20.0
18.6l,a;.a
17.79 17.02.ai.U 14.13 16.39,a;,U
13.67,e’ PO
As appears to.be usual in calculations of this kind, inner IP’s often do not correlate too well with.experiment, however the most loosely bound MO in each case is found to be e’, slightly u bonding between the halogen atoms, and not B as proposed by Armstrong and Perkins [4]. This work was supported by the National Research Council of Canada. The authors wish to thank Professor C. A. McDowell for advice and
111 For a description
of the instrument and method see D. C. Frost, C.A. McDowell and D.A. Vroom, Proc. Roy. Sot. A296 (1967) 566. J. Chem. Phys. 25 121 R. W. Law and J. L. Margrave. (1956) 1086. J. J. Kaufman and C. F. Pachucki, Journ. 131 U’.S.Koski. Am. Chem. Sot. 81 (1959) 1326. and P. G. Perkins, J. Chem.Soc. [41 D. R. Armstrong Al218 (1967). private communiI51 J. M. Sichel and M. A. Whitehead, cation. Their method (to be published) uses electron repulsion integrals calculated by the Ohno formula, atomic parameters derived from atomic spectra (JMS and MAW, Theoret. Chim. Acta 7 (1967) 32, and empirical binding parameters from bond energies of binary halides. 161 See: for instance, D. C. Frost, D. Mak and C. A. MC Dowell, Can. J. Chem. 40 (1962) 1064. (1953) 2301. 171 A. D. Walsh, J. Chem.Soc.
POTENTIALS
OF BPS, BC+
Ft.J. BOYD * and D. C. FBOST of Chemistr,, University of B. C., Vancouver 8, B.C., Received
1 March
AND BBr3 Canada
1968
The ionization potentials of BF3. BC13 and BBr3 have been found by photoelectron spectrometry, compared with those cakulated using an s and p electron semi-empirical SCF treatment.
We wish to present new values for the ionization potentials (IP’s) of BF3, BCl3 and BBr3 obtained by the photoelectron kinetic energy analysis
(PEKE)
technique
[l]
calculations include s and p orbitals orIy in the basis set and therefore may not be as satisfactory for BC13, BBr3 and BI3 as for BF3, depending on the extent to which d orbitals are invoLved in the first three. The PEEE first IP’s are in serious disagreement with the electron impact values (except for Law and Margrave’s IP for BCl3), however the PEKE values are strongly preferred. ELectron impact IP’s have been found to be in error before [6]. Assuming the e’ and e” orbitals to remain doubly degenerate, and the inner shell IF’s to lie above 20 eV, then six IP’s might be expected from our experiments (see Walsh [7f). The spectra give the expected number for BC13, but onLy five each for the other two. This may be due to instrumental inadequacy as far as resoLution is concerned (we are normally able to distinguish between states separated by 0.1 eV, however for these molecules there are indications of vibrational structure on many of the electronic bands and this may cause iI? masking).
and by calculations
using an all-valence-electron semi-empirical SCF treatment. Electron impact studies [2,3] on these molecules have yielded the first IP only, moreover where data from two laboratories can be compared (in the case of BC13) the agreement is poor. Armstrong and Perkins [4] have studied the ground state properties of the boron trihalides by the Pariser-Parr-Pople SCF method. They considered B electrons only, and they compared their calculated IP’s with the electron impact results mentioned above. The method of Sichel and Whitehead [ 51, which includes all valence electrons and predicts both z and 0 IP’s, has now been applied to these molecules, and the results are given in tables 1 and 2 with the symmetry designation of the MO’s and their classification symmetric or antisymmetric to the molecular plane (u or v). It should be mentioned that the
First
Ip’s
Table 1 of the boron trihalides
Electron impact BF3
15.5 (2)
BC13
10.9 (3).
BBr3
9.7 (3)
BI3
9.1 (3)
* Present address: Chemistry Department, University, Montreal, Canada. April
1968
PEKE (vertical IP)
12.0 (2)
and
(in eV) Theoretical
A and P [S]
15.95
160,
11.97
12.2. ir
12.68. 0
10.72
11.2, ii
11.47, o-
10.2, 7T
11.03, ff
McGill
649
7?
This work 16.05, 0
R. J. BOYD
650 Table 2 Tp’s of the boron trihalides (in eV)
PEKE (vert.) 15.95
BC13 BBr BF3 Calc. Calc. PEKE PEKE 8 ! ** this work (vert.) this work (vert.) thisazork 16_05,e’,o
16.65 16.69&o
11.97
12.68,e’.o
12.43 13.35&o
10.72
11.47,e’XJ
enco;lragement, and their colleagues for stimulating discussions. The permission of Drs. J. M. Sichel and M. A. Whitehead to use their method is gratefully acknowledged.
References
11.26 12.04&J
17.21 16.74.e”,n 12.77 13.50.e”,n 11.77 12.25.e”,lr 17_PS,e’.Q 14.50 14.74,$,~
and D. C. FROST
13.14 13.46,aG.n
19.0
17.90&.n
15.75 14.37,e’,U
20.0
18.6l,a;.a
17.79 17.02.ai.U 14.13 16.39,a;,U
13.67,e’ PO
As appears to.be usual in calculations of this kind, inner IP’s often do not correlate too well with.experiment, however the most loosely bound MO in each case is found to be e’, slightly u bonding between the halogen atoms, and not B as proposed by Armstrong and Perkins [4]. This work was supported by the National Research Council of Canada. The authors wish to thank Professor C. A. McDowell for advice and
111 For a description
of the instrument and method see D. C. Frost, C.A. McDowell and D.A. Vroom, Proc. Roy. Sot. A296 (1967) 566. J. Chem. Phys. 25 121 R. W. Law and J. L. Margrave. (1956) 1086. J. J. Kaufman and C. F. Pachucki, Journ. 131 U’.S.Koski. Am. Chem. Sot. 81 (1959) 1326. and P. G. Perkins, J. Chem.Soc. [41 D. R. Armstrong Al218 (1967). private communiI51 J. M. Sichel and M. A. Whitehead, cation. Their method (to be published) uses electron repulsion integrals calculated by the Ohno formula, atomic parameters derived from atomic spectra (JMS and MAW, Theoret. Chim. Acta 7 (1967) 32, and empirical binding parameters from bond energies of binary halides. 161 See: for instance, D. C. Frost, D. Mak and C. A. MC Dowell, Can. J. Chem. 40 (1962) 1064. (1953) 2301. 171 A. D. Walsh, J. Chem.Soc.