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The interaction of the N2O molecule with metal atoms: especially beryllium
ELSEVIER
Journal of Molecular Structure (Theochem) 312 (1994) 127-129
THEO CHEM
The interaction of the N 20 molecule with metal atoms: especially beryllium M. Blazej, N.H. March* Theoretical Chemistry Department, University of Oxford, 5 South Parks Road, Oxford OX] 3UB, UK
(Received 13 December 1993; accepted 24 December 1993)
Abstract Quantum chemical modelling of the N 2 0 molecule interacting with a beryllium atom in a linear configuration is presented. The interaction via both oxygen and nitrogen is considered, the latter being predicted as the lower energy configuration. A cluster of seven beryllium atoms was also considered, with the same conclusion. The equilibrium bond lengths were determined using the CNDOj2 semiempirical method and performing the geometry optimization. Finally, the N 2 0 molecule interacting with (a) one lithium atom and (b) one nickel atom again shows that bonding occurs via the nitrogen atoms.
1. Introduction
The present study is concerned with the interaction of the N 2 0 molecule with metal atoms, especially with beryllium. Some motivation for this work was provided by the current interest in surface science in N 2 0 chemisorbed on transition metal surfaces [1]. However, all the results presented here were obtained by quantum-chemical modelling of the N 20 molecule interacting with a small number of metal atoms. In the body of the paper, results are presented for beryllium only. However, in the Appendix, further results are given for lithium and for one transition element (nickel). 2. The N 2 0 molecule interacting with a single beryllium atom in linear geometry
In this section we consider the linear molecule * Corresponding author.
N 2 0 interacting with a single beryllium atom in purely linear geometrical configurations. We needed to determine whether it is more energetically favourable for the interaction to take place with the oxygen atom or with a nitrogen atom adjacent to the beryllium atom. Therefore we performed CNDOj2 calculations [2] and determined equilibrium bond lengths for the two possible linear geometries. The bond lengths are recorded in Table 1. Of course, CNDO is suitably parametrized, and we estimate that bond lengths can be determined within an error of about 10%. We conclude that it is more energetically favourable for a nitrogen atom to bond to the beryllium atom, the other orientation (O-Be) being a few electron-volts higher in energy (see also the results for lithium and for nickel in the Appendix). Although we feel confident in the prediction from CNDO that the metal atom interacts via the nitrogen atom in the linear geometry, it seemed of interest in view of surface science studies to mimic a
0166-1280/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0166-1280(94)03712-T
M. Blaze}. N.H. Marchlf. Mol. Struct. (Theochem) 312 (1994) 127-129
128
Table I Optimized bond lengths (A) for the linear N 2 0 molecule interacting with one beryllium atom (linear geometry)
N-N N-O Be-N2 O
N 2 0 bonded via N
N 2 0 bonded via
1.17
1.15
1.20
1.22
° N-N N-O Be-N 2O
1.77
1.73
cluster of atoms in the hexagonal close-packed beryllium. We thus made a calculation of the N 20 molecule interacting with a cluster of seven beryllium atoms (see below). 3. The N2 0 molecule interacting with a small cluster of beryllium atoms In this section we consider a small flat cluster of seven beryllium atoms arranged in a hexagonal close-packed structure (Fig. I). The N 20 molecule
•
•
•
•
Table 2 Optimized bond lengths (A) for the linear N 2 0 molecule interacting with a small beryllium cluster (seven atoms)
•
N 2 0 bonded via N
N 2 0 bonded via 0
1.16
1.16
1.21 2.04
1.22 2.48
was considered to be linear, perpendicular to the plane defined by the beryllium cluster, and to coincide with the C6v symmetry axis. Again, we wanted to determine whether it is more energetically favourable for the N 2 0 molecule to interact with the cluster via the oxygen atom or via a nitrogen atom. Hence we performed CNDOj2 calculations and determined the equilibrium bond lengths for these two geometries. The results are summarized in Table 2. It can be seen from the results that only the equilibrium distance of the beryllium cluster from the N 2 0 molecule was increased in comparison with the case of interaction with a single beryllium atom. Thus, the main conclusion still stands: it is more energetically favourable for the N 20 molecule to interact via the nitrogen end rather than via the oxygen atom, for which the energy is a few tenths of an electron-volt higher. The energy preference for interaction via the nitrogen end of the N 20 molecule was also confirmed for (a) a single lithium atom and (b) a single nickel atom (see Appendix).
4. Discussion and summary
•
•
<
> o
2.286 A Fig. I. A beryllium cluster consisting of seven atoms, modelling the surface of a hexagonal close-packed crystal structure.
As already noted, quantum-chemical modelling was carried out using the parametrized CNDO method. We have little doubt that N 20 interacts with beryllium atoms via the nitrogen end of N 20, and not via the oxygen atom. This conclusion is supported by the linear geometric configurations N-N-O-Be and O-N-N-Be, the latter being lower in energy by a few tenths of an electron-volt. The bond lengths in both configurations were determined. When the N 20 molecule interacts with a cluster of seven beryllium atoms, the same conclusion obtains. We also made similar calculations for lithium and for nickel. With one
M. Blazej, N.H. MarchlJ. Mol. Struct. (Theochem) 312 (1994) 127-129 Table 3 Optimized bond lengths (A) for the free linear N 2 0 molecule N-N N-O
1.16 1.21
atom of either, in linear geometry, the energetically favourable interaction is again via nitrogen. These results further increase the confidence in our conclusion. As the CNDO semiempirical method is quite approximate, we also optimized the geometry of the free N 2 0 molecule. The results are presented in Table 3. Our CNDO results are in good agreement with both experimental values of the equilibrium bond lengths [3] and values obtained from ab initio calculations [4]. Furthermore the electronic structure and the position of the oneelectron levels for the N 2 0 molecule in free space are in very good agreement with those presented previously [4]. This supports our belief that the CNDO calculations performed in the present study reflect the nature of the bonding and the quantum-chemical principles involved quite well. In particular, we are confident that the predicted equilibrium bond lengths are correct, and thus these should be of experimental interest too. Although less reliable than the bond lengths, the total energies calculated in the present study reveal differences of a few tenths of an electron-volt between the two geometries considered. This leads us to conclude that the favourable configuration for the N 2 0 molecule interacting with metals is via the nitrogen end. The results presented in the Appendix indicate that this is a general result, holding also for lithium and for nickel.
nitrogen rather than oxygen, and we are both most grateful to him for his continuing interest. M.B. would like to thank Professor L. Skala from Charles University, Prague, for kindly providing the CNDO computer program and for useful comments. Appendix: the N 2 0 molecule interacting with single lithium and nickel atoms The CNDO optimized bond lengths are summarized in Tables Al and A2 for a linear N 20 molecule interacting with a single lithium atom and a single nickel atom, respectively, in completely linear geometry. Note that, while the N-O bond lengths are very close to those given in Table 1, the N-N distances are somewhat larger than the value given in Table 1 for beryllium. Table Al Optimized bond lengths (A) for the linear N 2 0 molecule interacting with one lithium atom N 2 0 bonded via N
N 2 0 bonded via
1.22 1.21 1.94
1.15 1.22 2.43
°
Table A2 Optimized bond lengths (A) for the linear N 20 molecule interacting with one nickel atom
Acknowledgements N.H.M. wishes to thank Professor Z. Gortel for drawing his attention, during a visit to the Physics Department, University of Alberta, Edmonton, in the Autumn of 1992, to the current interest in the N 2 0 molecule interacting with metal atoms. Professor D. Menzel, in stimulating correspondence, first drew our attention to the likelihood that the bonding with transition metal atoms would be via
129
N 2 0 bonded via N
N 20 bonded via
1.29 1.20 1.59
1.15 1.23 1.73
°
References [I] E. Umbach and D. Menzel, Chern. Phys. Lett., 84 (1981) 491. [2] l.A. Pople and G.A. Segal, l. Chern. Phys., 43 (Suppl) (1965) 136; 44 (1966) 3289. [3] L.E. Sutton, Interatomic Distances, The Chemical Society, London, 1958; Supplement, 1965. [4] S.D. Peyerimhoff and R.l. Buenker, l. Chern. Phys., 49 (1968) 2473.
Journal of Molecular Structure (Theochem) 312 (1994) 127-129
THEO CHEM
The interaction of the N 20 molecule with metal atoms: especially beryllium M. Blazej, N.H. March* Theoretical Chemistry Department, University of Oxford, 5 South Parks Road, Oxford OX] 3UB, UK
(Received 13 December 1993; accepted 24 December 1993)
Abstract Quantum chemical modelling of the N 2 0 molecule interacting with a beryllium atom in a linear configuration is presented. The interaction via both oxygen and nitrogen is considered, the latter being predicted as the lower energy configuration. A cluster of seven beryllium atoms was also considered, with the same conclusion. The equilibrium bond lengths were determined using the CNDOj2 semiempirical method and performing the geometry optimization. Finally, the N 2 0 molecule interacting with (a) one lithium atom and (b) one nickel atom again shows that bonding occurs via the nitrogen atoms.
1. Introduction
The present study is concerned with the interaction of the N 2 0 molecule with metal atoms, especially with beryllium. Some motivation for this work was provided by the current interest in surface science in N 2 0 chemisorbed on transition metal surfaces [1]. However, all the results presented here were obtained by quantum-chemical modelling of the N 20 molecule interacting with a small number of metal atoms. In the body of the paper, results are presented for beryllium only. However, in the Appendix, further results are given for lithium and for one transition element (nickel). 2. The N 2 0 molecule interacting with a single beryllium atom in linear geometry
In this section we consider the linear molecule * Corresponding author.
N 2 0 interacting with a single beryllium atom in purely linear geometrical configurations. We needed to determine whether it is more energetically favourable for the interaction to take place with the oxygen atom or with a nitrogen atom adjacent to the beryllium atom. Therefore we performed CNDOj2 calculations [2] and determined equilibrium bond lengths for the two possible linear geometries. The bond lengths are recorded in Table 1. Of course, CNDO is suitably parametrized, and we estimate that bond lengths can be determined within an error of about 10%. We conclude that it is more energetically favourable for a nitrogen atom to bond to the beryllium atom, the other orientation (O-Be) being a few electron-volts higher in energy (see also the results for lithium and for nickel in the Appendix). Although we feel confident in the prediction from CNDO that the metal atom interacts via the nitrogen atom in the linear geometry, it seemed of interest in view of surface science studies to mimic a
0166-1280/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0166-1280(94)03712-T
M. Blaze}. N.H. Marchlf. Mol. Struct. (Theochem) 312 (1994) 127-129
128
Table I Optimized bond lengths (A) for the linear N 2 0 molecule interacting with one beryllium atom (linear geometry)
N-N N-O Be-N2 O
N 2 0 bonded via N
N 2 0 bonded via
1.17
1.15
1.20
1.22
° N-N N-O Be-N 2O
1.77
1.73
cluster of atoms in the hexagonal close-packed beryllium. We thus made a calculation of the N 20 molecule interacting with a cluster of seven beryllium atoms (see below). 3. The N2 0 molecule interacting with a small cluster of beryllium atoms In this section we consider a small flat cluster of seven beryllium atoms arranged in a hexagonal close-packed structure (Fig. I). The N 20 molecule
•
•
•
•
Table 2 Optimized bond lengths (A) for the linear N 2 0 molecule interacting with a small beryllium cluster (seven atoms)
•
N 2 0 bonded via N
N 2 0 bonded via 0
1.16
1.16
1.21 2.04
1.22 2.48
was considered to be linear, perpendicular to the plane defined by the beryllium cluster, and to coincide with the C6v symmetry axis. Again, we wanted to determine whether it is more energetically favourable for the N 2 0 molecule to interact with the cluster via the oxygen atom or via a nitrogen atom. Hence we performed CNDOj2 calculations and determined the equilibrium bond lengths for these two geometries. The results are summarized in Table 2. It can be seen from the results that only the equilibrium distance of the beryllium cluster from the N 2 0 molecule was increased in comparison with the case of interaction with a single beryllium atom. Thus, the main conclusion still stands: it is more energetically favourable for the N 20 molecule to interact via the nitrogen end rather than via the oxygen atom, for which the energy is a few tenths of an electron-volt higher. The energy preference for interaction via the nitrogen end of the N 20 molecule was also confirmed for (a) a single lithium atom and (b) a single nickel atom (see Appendix).
4. Discussion and summary
•
•
<
> o
2.286 A Fig. I. A beryllium cluster consisting of seven atoms, modelling the surface of a hexagonal close-packed crystal structure.
As already noted, quantum-chemical modelling was carried out using the parametrized CNDO method. We have little doubt that N 20 interacts with beryllium atoms via the nitrogen end of N 20, and not via the oxygen atom. This conclusion is supported by the linear geometric configurations N-N-O-Be and O-N-N-Be, the latter being lower in energy by a few tenths of an electron-volt. The bond lengths in both configurations were determined. When the N 20 molecule interacts with a cluster of seven beryllium atoms, the same conclusion obtains. We also made similar calculations for lithium and for nickel. With one
M. Blazej, N.H. MarchlJ. Mol. Struct. (Theochem) 312 (1994) 127-129 Table 3 Optimized bond lengths (A) for the free linear N 2 0 molecule N-N N-O
1.16 1.21
atom of either, in linear geometry, the energetically favourable interaction is again via nitrogen. These results further increase the confidence in our conclusion. As the CNDO semiempirical method is quite approximate, we also optimized the geometry of the free N 2 0 molecule. The results are presented in Table 3. Our CNDO results are in good agreement with both experimental values of the equilibrium bond lengths [3] and values obtained from ab initio calculations [4]. Furthermore the electronic structure and the position of the oneelectron levels for the N 2 0 molecule in free space are in very good agreement with those presented previously [4]. This supports our belief that the CNDO calculations performed in the present study reflect the nature of the bonding and the quantum-chemical principles involved quite well. In particular, we are confident that the predicted equilibrium bond lengths are correct, and thus these should be of experimental interest too. Although less reliable than the bond lengths, the total energies calculated in the present study reveal differences of a few tenths of an electron-volt between the two geometries considered. This leads us to conclude that the favourable configuration for the N 2 0 molecule interacting with metals is via the nitrogen end. The results presented in the Appendix indicate that this is a general result, holding also for lithium and for nickel.
nitrogen rather than oxygen, and we are both most grateful to him for his continuing interest. M.B. would like to thank Professor L. Skala from Charles University, Prague, for kindly providing the CNDO computer program and for useful comments. Appendix: the N 2 0 molecule interacting with single lithium and nickel atoms The CNDO optimized bond lengths are summarized in Tables Al and A2 for a linear N 20 molecule interacting with a single lithium atom and a single nickel atom, respectively, in completely linear geometry. Note that, while the N-O bond lengths are very close to those given in Table 1, the N-N distances are somewhat larger than the value given in Table 1 for beryllium. Table Al Optimized bond lengths (A) for the linear N 2 0 molecule interacting with one lithium atom N 2 0 bonded via N
N 2 0 bonded via
1.22 1.21 1.94
1.15 1.22 2.43
°
Table A2 Optimized bond lengths (A) for the linear N 20 molecule interacting with one nickel atom
Acknowledgements N.H.M. wishes to thank Professor Z. Gortel for drawing his attention, during a visit to the Physics Department, University of Alberta, Edmonton, in the Autumn of 1992, to the current interest in the N 2 0 molecule interacting with metal atoms. Professor D. Menzel, in stimulating correspondence, first drew our attention to the likelihood that the bonding with transition metal atoms would be via
129
N 2 0 bonded via N
N 20 bonded via
1.29 1.20 1.59
1.15 1.23 1.73
°
References [I] E. Umbach and D. Menzel, Chern. Phys. Lett., 84 (1981) 491. [2] l.A. Pople and G.A. Segal, l. Chern. Phys., 43 (Suppl) (1965) 136; 44 (1966) 3289. [3] L.E. Sutton, Interatomic Distances, The Chemical Society, London, 1958; Supplement, 1965. [4] S.D. Peyerimhoff and R.l. Buenker, l. Chern. Phys., 49 (1968) 2473.