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Ab initio calculations on CICN and ONCI
Volume 40, htiber
CHEMCCALPHYSICS LETTERS
3
AB INITLO CALCULATIQNS
Department
of Chemistry.
-15 June 1976.
ON CICN AND ONQ
The University of Bergen. lK5014 Bergen, Norway
Received 23 December 197.5 Revised manuscript received 12 March 1976
Ab initio calculations are presented for the mo?eculesClCN and ONCI with optimization of all geometric parameters. Calculated equilibrium geometries for CICN are in good agreement with microwave data; however, the calculated N-Cl distance in ONCLis about 0.1 A shorter than obtained by electron diffraction. Orbittl energies are calculated by means of Koopmans’ theorem and also by ASCF calculations. The importance of relaxation energy is shown by comparing culated orbital energies with experimental data from photoelectron spectra of the valence levels.
1. Introduction A molecular
orbital interpretation
of X-ray emis-
sion spectra of ClCN and ONCl was previously done [l] . The calculated spectra from the ab initio wavefunctions were found to be in excellent agreement with experiments. This report includes the details of the ab initio calculations using fairly extended gaussian basis set on these two molecules_ A full geometry optimization is performed and compared with experimental data. Experimental photoionization energies are available for both CICN [2,3]
and for ONCl [4,5].
The compari-
son with the experiments is first performed with Koopmans’ theorem [6] results for the neutral molecules. In addition the importance of electronic reorganization is investigated. This is achieved by performing direct calculations on the valence ionized states. The ionization energy is then given by the difference in the total energy of the ion and the mofecule.
2. Calculations The calculations were performed with the program system MOLECULE [7] _The molecular orbitals were expanded in gaussian functions. 9s: and SpYtype func-
the cal-
tions were contracted to a 4s2p basis for carbon, nitrogen, and oxygen. The orbital exponents and contraction coefficients used were those given by Dunning [S] . A 12~9~ basis given by VeiLlard [!J] was con-
tracted to 6s4p for chlorine. In addition, a series of calculations was performed on the two molecules with one set of d-orbitals added to the chlorine basis set which used exponents 0.68 [lo]. A full geometry optimization was performed on both molecules in the ground state and with the two basis sets. The open shell calculations were performed with the SCF program UiBMOL [l I]. Convergence problems were solved by interpolating on the density matrix 1121 and with level shifts [ 131. The calculations were performed on the Univac 1110 computer at the University of Bergen.
3. Results and discussions
3.1. CKYi The cyanogen chloride molecule is linear and belongs to the symmetry group C,,. The total energies and the results of the geometrical optimization are shown in tabIe 1. With the basis sets used, the total energy is lowered t?y 0.03 au when a set of d-orbit& on chlorine is. added to the basis set. The C-N distance came out 429
Volume 40,.number 3
.-Table 1 .. Calculated total energies and optimd bond distances for ClCN compared to experimental values
no 3dCI with 3dC1 ref. [ISI exp, ref. [ 14 ]
15 junc 1976
CXEMICAL PHYSICS LETTERS
-E (au)
Cl-C(A)
C-NW
551.65623 551.68677 551.82472
1.684 1.657 1.629 1.630
1.150 1.151 1.163 1.163
almost the same for the two basis sets, while the Cl-C distance was decreased by about 0.03 A to 1.657 A when 3dCl was included. This Cl-C distance is in good agreement with the experimental microwave data where a Cl-C distance is reported to be 1.630 A [ 141. An extended doubie zeta Slater-type calculation is reported for ClCN by McLean and Yoshimine [15]. In their calcdation 3d and 4f functions on each atom were included in the basis set. Their results of geometry optimization are listed in table 1 iogether with the result of this work and experimental data. Population analysis was performed on CICN with tile two basis sets and in the minimum energy configuration. The gross atomic charge on the chlorine atom in ClCN is + 0.06 electrons while both nitrogen and carbon has a small negative gross atomic charge. The chlorine 3d population is very small. There is no great difference in the population analysis with and without d-orbitab on chlorine.
Orbital energies calculated in the minirnlun energy geometry. are shown in table 2 together with experimental ionization potentials- The two first-columns show the Koopmans“theorem result performed with the two basis sets. The third column is the difference between the neutral molecule and the ionized state calculated with 3dCI included in the basis set. The ordering of the orbitals was the same for the different calculations and the assignments are the same as indicated in the papers of photoelectron measurements. There are small differences in the Koopmans’ theorem results for the two basis sets, but no regular trends compared to the experimental results. The importance of the relaxation energy is nicely shown. All the ASCF results are in much better agreement with the experimental results than Koopmans’ ionization energies. Clark and Scanlan have studied the electronic reorganization which accompany both core and valence ionization on pyridine. They, too, found the Koopmans’theorem resuits were not basis set dependent, and they show the importance of the electronic reorganization 1161. 3.2. ONcl The nitrosyl chloride moIecule is planar and belongs to the C, symmetry group. To the best of the author’s knowledge, no ab initio calculations have been reported previously for the ONCl molecule. The results of the present ab initio geometrical optirnization are given iu table 3 together with experimental electron-diffraction data on this molecule 1171. The
Table 2 Orbits! energies and ionization potentiais (eW for CICN calculated in minimum energy configutation -_o Orbital
no 3dCl
with 3dCl
lo
20 30 4u 5a
2854.47 425.79 309.42 289.55 220.87
28X32 425.62 309.36 289.37 220.72
1X 60 70 8a 23 90 3n
220.76 35.47 32.79 19.99 16.37 16.02 13.11
220.6 1 35.46 32.72 20.46 16.39 15.94 12.58
ASCF
&P-
with 3dCl
ref. [Z]
ref_I3]
19.34 15.60
19.03 15.38 13.80 12.34
19.00 15.37 13.80 12.37
-13.57 _ 11.99
Table 3 Calculated total energies and optimaTbond distances for ONCl
compared to experimenial values
no 3dC1 with 3dC1 exp, ref. ] 171
15 June
CHEhilCAL PHYSKS LETTERS
Volume 40, number 3
-E(au)
O-N(A)
N-Cl(A)
LONCI
588.60635 588.62036
1.148 1.164 1.14
1.961 1.856 1.95
114” 114” 116’
total. energy is lowered by 0.014 au when 3d on chlorine is included in the basis set. The O-N distance optimized without 3dCL is found to be 1.148 A while it is increased to 1.I64 i(. when 3dC1 is included. The experimental value is 1 .I4 A indicating a better correlation when 3dC1 is excluded. The N-Cl distance is decreased by 0.105 8, when 3dCl is incliuded. This result is not in good agreement with available experimental data for this molecule. The N-Cl distance is found to be 1.95 (1) A compared to the calculated value 1.856 A. However, the calculations indicate that this bond is weak since the energy minimum is quite “flat”- The decrease in a distance by about 0.1 A when 3d polarization functions are added to one of the atoms in the bond is not unexpected. Rohmer and Roos’ calculations of three-membered ring compounds including sulphur show the same trend 1181. They found a decrease in the C-S bond length by
1976
0.1 A when d-orbitals on sulphur were included in the basis set. Though slightly different angles and distances have been obtained from more recent microwave spectra [19], the values are not too reliable, since ordy the two largest moments of inertia of the molecule could be obtained directly from the spectra, whereas the third must be calculated relatively inaccurately from the other two. Compared to other N--Cl bond distances in other compounds they appear to be shorter, e.g. the N-Cl bond in N02Cl is reported to be 1.840 A from microwave data [20] _ Taking an average value of other N-Cl bonds one gets the value of 1.75 A [20]. The result of the population analysis for ONCl shows that the chlorine atom has a slightly negative charge of -0.07 electrons. The oxygen atom has also a negative gross atomic charge while the nitrogen comes out with +0.18 electrons. The C13d occupation is very small and here as in the case of ClCN the difference in the population analysis with and without 3dCl is very small. The results of the calculated orbital energies for ONCl in its minimum energy configuration are listed in table 4, together with the experimental ionization potentials. The ordering of the orbitals was the same for the different calculations (semiempirical calculaabout
Table 4 Orbital energies and ionization potentials (eV) for ONCI calculated in minimum energy configuration --E
Orbital
no 3dCl
with 3dCl
la’ 2a’
2852.43 565.06_ 431.82 287.23 218.50 2 18.42 219.41 46.72 30.60 26.30 21.20 20.47 19.71 12.86 12.82 11.94
2852.84 564.23 431.05 286.66 218.94 218.85 218.84 45.81 3i.27 25.84 20.82 20.03 19.06 13.20 13.14 12:u?
3a’ 4a’ Sa’ 1a” 6a’ 7a’ 8a’ 9a’ 10a’ lla’ 2a” 12a’ 3a” 13a’
A SCF
Exp.
with 3dC1
ref. (41
ref. [5]
19.17 18.18
18.8 17.0 15.9 11.4 11.4 11.4
18.97 17.13 16.15 11.5 11.5 11.5
11.22 11.47 11.44 IL.32
431
_volilm;4b,-n~miJer~
:
gave moth&
:tions
-. order&
CHEMICAL PHYSICS’LE’ITERS
:
of’&e
levels
[l J .,There,
[7] ’ [S] [9]
is
appreciabkdiffererke for the two basis sets when KOO~IT&S’theorerii is used. Also in_ this case,‘ the ASCF-results are in much better agreement with the exiejinental ionjzation potentials.than the Koapmans’ fheorem results, indicating the importance of the re--
fl] A. St&&d, Cbem. Phys. Letters 36 (1975) 357. f2] R-F. 3_ake and I-I. Thompson, Proc. Roy. Sot. A 317
.
(1976) 187. E. IIeabronner,
V. Hornun~ and K-A. Muszkat, HeIv. Chim. Acta 54 (1970) 347. f4] II. Bergmann, S. EEbeI and R. Demuth, in preparation.
[S] DC. Frost, S-T. Lee, CA_ McDowell and N.P.C. J. Electron Spectry. Physica 1 f1933)
7 (197.5) 331.
f6] T. Fioopmans,
104.
.-
:
_-_
. .’
._
_. I
_’ .:
of Stockholm
[14] A.G. Smith, I-I. Ring, W.V. Smith and W. Cordy, Phys. Rev. 74 (1948) 1113. fl!!] A.D. McLean and M. Yoshimine, IBhI J. Res. Develop. Suppl. (1967). [16] D.T. Clark and 1-W. ScanIan, J. Chem. Sot. Faraday Trans. 70 (1974) 1222. [17] J.A.A. Ketefaar and K.J. Palmer, J. Am. Chem. Sot. 59 (1937) 2629. [ 181 M.M. Rohmer and B. Roos, 3. Am. Chem. Sot. 97 (1975) 2025. [ 191 J.D. Rogers and D. Williams,1. Chem. Phys. 34 (1961) 2195. 2201 L-E. Sutton, ed., Tables of interatomic distances, Suppl. (Chem. Soc., London, 1965). 1956-1959
References
&
Univetsiv
[ 121 J, AlmlBf,private communication.’ [ 13) K. Faegri Jr., private communication.
luxation energy.
Westwood,
J. AlmlSf, USlP report 72-09,
(1972): T&I. Dunning, 3. C&m. Physi53 (1970) 2823. A. Veillard, Theoret. Chim. Acta 12 (1968) 405. [IO] B. Roos and P. Siegbahn, Theoret. Chim. Acta 17 (1970) 199. [I1 1 K Faegri Jr. and R. Marine, Mol. Phys., to be published.
:‘no
j3]
I.5 June 1976.
:
: .
CHEMCCALPHYSICS LETTERS
3
AB INITLO CALCULATIQNS
Department
of Chemistry.
-15 June 1976.
ON CICN AND ONQ
The University of Bergen. lK5014 Bergen, Norway
Received 23 December 197.5 Revised manuscript received 12 March 1976
Ab initio calculations are presented for the mo?eculesClCN and ONCI with optimization of all geometric parameters. Calculated equilibrium geometries for CICN are in good agreement with microwave data; however, the calculated N-Cl distance in ONCLis about 0.1 A shorter than obtained by electron diffraction. Orbittl energies are calculated by means of Koopmans’ theorem and also by ASCF calculations. The importance of relaxation energy is shown by comparing culated orbital energies with experimental data from photoelectron spectra of the valence levels.
1. Introduction A molecular
orbital interpretation
of X-ray emis-
sion spectra of ClCN and ONCl was previously done [l] . The calculated spectra from the ab initio wavefunctions were found to be in excellent agreement with experiments. This report includes the details of the ab initio calculations using fairly extended gaussian basis set on these two molecules_ A full geometry optimization is performed and compared with experimental data. Experimental photoionization energies are available for both CICN [2,3]
and for ONCl [4,5].
The compari-
son with the experiments is first performed with Koopmans’ theorem [6] results for the neutral molecules. In addition the importance of electronic reorganization is investigated. This is achieved by performing direct calculations on the valence ionized states. The ionization energy is then given by the difference in the total energy of the ion and the mofecule.
2. Calculations The calculations were performed with the program system MOLECULE [7] _The molecular orbitals were expanded in gaussian functions. 9s: and SpYtype func-
the cal-
tions were contracted to a 4s2p basis for carbon, nitrogen, and oxygen. The orbital exponents and contraction coefficients used were those given by Dunning [S] . A 12~9~ basis given by VeiLlard [!J] was con-
tracted to 6s4p for chlorine. In addition, a series of calculations was performed on the two molecules with one set of d-orbitals added to the chlorine basis set which used exponents 0.68 [lo]. A full geometry optimization was performed on both molecules in the ground state and with the two basis sets. The open shell calculations were performed with the SCF program UiBMOL [l I]. Convergence problems were solved by interpolating on the density matrix 1121 and with level shifts [ 131. The calculations were performed on the Univac 1110 computer at the University of Bergen.
3. Results and discussions
3.1. CKYi The cyanogen chloride molecule is linear and belongs to the symmetry group C,,. The total energies and the results of the geometrical optimization are shown in tabIe 1. With the basis sets used, the total energy is lowered t?y 0.03 au when a set of d-orbit& on chlorine is. added to the basis set. The C-N distance came out 429
Volume 40,.number 3
.-Table 1 .. Calculated total energies and optimd bond distances for ClCN compared to experimental values
no 3dCI with 3dC1 ref. [ISI exp, ref. [ 14 ]
15 junc 1976
CXEMICAL PHYSICS LETTERS
-E (au)
Cl-C(A)
C-NW
551.65623 551.68677 551.82472
1.684 1.657 1.629 1.630
1.150 1.151 1.163 1.163
almost the same for the two basis sets, while the Cl-C distance was decreased by about 0.03 A to 1.657 A when 3dCl was included. This Cl-C distance is in good agreement with the experimental microwave data where a Cl-C distance is reported to be 1.630 A [ 141. An extended doubie zeta Slater-type calculation is reported for ClCN by McLean and Yoshimine [15]. In their calcdation 3d and 4f functions on each atom were included in the basis set. Their results of geometry optimization are listed in table 1 iogether with the result of this work and experimental data. Population analysis was performed on CICN with tile two basis sets and in the minimum energy configuration. The gross atomic charge on the chlorine atom in ClCN is + 0.06 electrons while both nitrogen and carbon has a small negative gross atomic charge. The chlorine 3d population is very small. There is no great difference in the population analysis with and without d-orbitab on chlorine.
Orbital energies calculated in the minirnlun energy geometry. are shown in table 2 together with experimental ionization potentials- The two first-columns show the Koopmans“theorem result performed with the two basis sets. The third column is the difference between the neutral molecule and the ionized state calculated with 3dCI included in the basis set. The ordering of the orbitals was the same for the different calculations and the assignments are the same as indicated in the papers of photoelectron measurements. There are small differences in the Koopmans’ theorem results for the two basis sets, but no regular trends compared to the experimental results. The importance of the relaxation energy is nicely shown. All the ASCF results are in much better agreement with the experimental results than Koopmans’ ionization energies. Clark and Scanlan have studied the electronic reorganization which accompany both core and valence ionization on pyridine. They, too, found the Koopmans’theorem resuits were not basis set dependent, and they show the importance of the electronic reorganization 1161. 3.2. ONcl The nitrosyl chloride moIecule is planar and belongs to the C, symmetry group. To the best of the author’s knowledge, no ab initio calculations have been reported previously for the ONCl molecule. The results of the present ab initio geometrical optirnization are given iu table 3 together with experimental electron-diffraction data on this molecule 1171. The
Table 2 Orbits! energies and ionization potentiais (eW for CICN calculated in minimum energy configutation -_o Orbital
no 3dCl
with 3dCl
lo
20 30 4u 5a
2854.47 425.79 309.42 289.55 220.87
28X32 425.62 309.36 289.37 220.72
1X 60 70 8a 23 90 3n
220.76 35.47 32.79 19.99 16.37 16.02 13.11
220.6 1 35.46 32.72 20.46 16.39 15.94 12.58
ASCF
&P-
with 3dCl
ref. [Z]
ref_I3]
19.34 15.60
19.03 15.38 13.80 12.34
19.00 15.37 13.80 12.37
-13.57 _ 11.99
Table 3 Calculated total energies and optimaTbond distances for ONCl
compared to experimenial values
no 3dC1 with 3dC1 exp, ref. ] 171
15 June
CHEhilCAL PHYSKS LETTERS
Volume 40, number 3
-E(au)
O-N(A)
N-Cl(A)
LONCI
588.60635 588.62036
1.148 1.164 1.14
1.961 1.856 1.95
114” 114” 116’
total. energy is lowered by 0.014 au when 3d on chlorine is included in the basis set. The O-N distance optimized without 3dCL is found to be 1.148 A while it is increased to 1.I64 i(. when 3dC1 is included. The experimental value is 1 .I4 A indicating a better correlation when 3dC1 is excluded. The N-Cl distance is decreased by 0.105 8, when 3dCl is incliuded. This result is not in good agreement with available experimental data for this molecule. The N-Cl distance is found to be 1.95 (1) A compared to the calculated value 1.856 A. However, the calculations indicate that this bond is weak since the energy minimum is quite “flat”- The decrease in a distance by about 0.1 A when 3d polarization functions are added to one of the atoms in the bond is not unexpected. Rohmer and Roos’ calculations of three-membered ring compounds including sulphur show the same trend 1181. They found a decrease in the C-S bond length by
1976
0.1 A when d-orbitals on sulphur were included in the basis set. Though slightly different angles and distances have been obtained from more recent microwave spectra [19], the values are not too reliable, since ordy the two largest moments of inertia of the molecule could be obtained directly from the spectra, whereas the third must be calculated relatively inaccurately from the other two. Compared to other N--Cl bond distances in other compounds they appear to be shorter, e.g. the N-Cl bond in N02Cl is reported to be 1.840 A from microwave data [20] _ Taking an average value of other N-Cl bonds one gets the value of 1.75 A [20]. The result of the population analysis for ONCl shows that the chlorine atom has a slightly negative charge of -0.07 electrons. The oxygen atom has also a negative gross atomic charge while the nitrogen comes out with +0.18 electrons. The C13d occupation is very small and here as in the case of ClCN the difference in the population analysis with and without 3dCl is very small. The results of the calculated orbital energies for ONCl in its minimum energy configuration are listed in table 4, together with the experimental ionization potentials. The ordering of the orbitals was the same for the different calculations (semiempirical calculaabout
Table 4 Orbital energies and ionization potentials (eV) for ONCI calculated in minimum energy configuration --E
Orbital
no 3dCl
with 3dCl
la’ 2a’
2852.43 565.06_ 431.82 287.23 218.50 2 18.42 219.41 46.72 30.60 26.30 21.20 20.47 19.71 12.86 12.82 11.94
2852.84 564.23 431.05 286.66 218.94 218.85 218.84 45.81 3i.27 25.84 20.82 20.03 19.06 13.20 13.14 12:u?
3a’ 4a’ Sa’ 1a” 6a’ 7a’ 8a’ 9a’ 10a’ lla’ 2a” 12a’ 3a” 13a’
A SCF
Exp.
with 3dC1
ref. (41
ref. [5]
19.17 18.18
18.8 17.0 15.9 11.4 11.4 11.4
18.97 17.13 16.15 11.5 11.5 11.5
11.22 11.47 11.44 IL.32
431
_volilm;4b,-n~miJer~
:
gave moth&
:tions
-. order&
CHEMICAL PHYSICS’LE’ITERS
:
of’&e
levels
[l J .,There,
[7] ’ [S] [9]
is
appreciabkdiffererke for the two basis sets when KOO~IT&S’theorerii is used. Also in_ this case,‘ the ASCF-results are in much better agreement with the exiejinental ionjzation potentials.than the Koapmans’ fheorem results, indicating the importance of the re--
fl] A. St&&d, Cbem. Phys. Letters 36 (1975) 357. f2] R-F. 3_ake and I-I. Thompson, Proc. Roy. Sot. A 317
.
(1976) 187. E. IIeabronner,
V. Hornun~ and K-A. Muszkat, HeIv. Chim. Acta 54 (1970) 347. f4] II. Bergmann, S. EEbeI and R. Demuth, in preparation.
[S] DC. Frost, S-T. Lee, CA_ McDowell and N.P.C. J. Electron Spectry. Physica 1 f1933)
7 (197.5) 331.
f6] T. Fioopmans,
104.
.-
:
_-_
. .’
._
_. I
_’ .:
of Stockholm
[14] A.G. Smith, I-I. Ring, W.V. Smith and W. Cordy, Phys. Rev. 74 (1948) 1113. fl!!] A.D. McLean and M. Yoshimine, IBhI J. Res. Develop. Suppl. (1967). [16] D.T. Clark and 1-W. ScanIan, J. Chem. Sot. Faraday Trans. 70 (1974) 1222. [17] J.A.A. Ketefaar and K.J. Palmer, J. Am. Chem. Sot. 59 (1937) 2629. [ 181 M.M. Rohmer and B. Roos, 3. Am. Chem. Sot. 97 (1975) 2025. [ 191 J.D. Rogers and D. Williams,1. Chem. Phys. 34 (1961) 2195. 2201 L-E. Sutton, ed., Tables of interatomic distances, Suppl. (Chem. Soc., London, 1965). 1956-1959
References
&
Univetsiv
[ 121 J, AlmlBf,private communication.’ [ 13) K. Faegri Jr., private communication.
luxation energy.
Westwood,
J. AlmlSf, USlP report 72-09,
(1972): T&I. Dunning, 3. C&m. Physi53 (1970) 2823. A. Veillard, Theoret. Chim. Acta 12 (1968) 405. [IO] B. Roos and P. Siegbahn, Theoret. Chim. Acta 17 (1970) 199. [I1 1 K Faegri Jr. and R. Marine, Mol. Phys., to be published.
:‘no
j3]
I.5 June 1976.
:
: .