| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
Nature |
|---|---|---|---|
| Cs CORINA | -233.282,026 | -233.130,937 | global minimum |
| Cs | -233.280,442 | -233.129,881 | saddle point |
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| http://www.ijms.org | Int. J. Mol. Sci.2004, 5, 110-118 |
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Ab initio study of alkyl-oxonium cations
CnH2n+1OH2+,
n=1,2,3,4
GEOMETRY OPTIMIZATIONS |
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COMPUTATIONAL STRATEGY |
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Concerning the MethylOxonium Cation, a symmetric Cs geometry seems a rather obvious choice. We nevertheless optimized with and without a Cs symmetry constraint, as expected the geometry and energy are the same. The vibronic energy is the sum of the electronic energy and the vibrational Zero-Point-Energy (ZPE), computed within the framework of the adiabatic approximation and the harmonic approximation. The fact that the ZPE is very slightly lower in magnitude in the Cs geometry is just an artefact.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
|---|---|---|
| C1 CORINA | -115,693.616 | -115.627,745 |
| Cs CORINA | -115,693.616 | -115.627,746 |
Concerning the EthylOxonium Cation, we started from the structure proposed by CORINA which appears as a reasoable guess. The ZPE is 0.094,880 Hartree.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
|---|---|---|
| C1 CORINA | -154.889,501 | -154,794,621 |
Concerning the 1-PropylOxonium Cation, we started from the structure proposed by CORINA without symmetry constraint. The ZPE is 0,124.270 Hartree. The initial and final geometries seem quite reasonable, and no other geometries were investigated.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
|---|---|---|
| C1 CORINA | -194.074,869 | -194.049,401 |
Concerning the 2-PropylOxonium Cation, we started from the structure proposed by CORINA which is asymmetric. We tried yet another geometry where hydrogen atoms nearby the oxygen atoms are located respectively on each side of a symmetry plane. This Cs structure features a lower energy. It appears that CORINA failed to guess the optimized geometry in this case.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
|---|---|---|
| C1 CORINA | -194,085.307 | -193.962,213 |
| Cs | -194,085.994 | -193,962.813 |
1-ButylOxonium Cation:
We kept the structure proposed by
CORINA.
It seems difficult to envision any other reasonable candidate geometry.
Trying to impose an overall Cs symmetry would require two pair of hydrogen atoms to
face one another.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
|---|---|---|
| C1 CORINA | -233.259,678 | -233.106,238 |
2-ButylOxonium Cation: We considered two types of geometries : the first one is being proposed by CORINA, while the second one is obtained from the former geometry by a 120° rotation of the oxonium group. The overall molecule does not posses a sigma plane. In the vicinity of the oxonium group however, it looks almost as if there were a Cs symmetry, therefore we took the liberty to label it as "nearly Cs" to distinguish it from the first geometry proposed by CORINA. This latter geometry features a lower energy. Consideration of the ZPE brings further advantage to the "nearly Cs" geometry. It appears that CORINA again failed to guess the optimized geometry.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
Nature |
|---|---|---|---|
| C1 CORINA | -233,271.199 | -233,118.970 | local minimum |
| nearly Cs | -233,271.777 | -233,119.432 | global minimum |
IsoButylOxonium Cation : We considered four types of geometry. The first one is an asymmetric geometry proposed by CORINA Since this molecule, at a very first glance, could feature a symmetry plane, we explored also three other more symmetric geometries. The geometry proposed by CORINA however prevailed as the best geometry for a global minimum.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
Nature |
|---|---|---|---|
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C1 CORINA |
-233.263,333 | -233.110,484 | global minimum |
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Cs type A |
-233.255,232 | -233.102,368 | saddle point |
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Cs type B |
-233.262,854 | -233.110,094 | local minimum |
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Cs type C |
-233.260,681 | -233.108,464 | saddle point |
TertButylOxonium Cation : CORINA suggested a very reasonable Cs symmetric structure. We also explored another Cs symmetric structure which turned to be, as expected, a saddle point.
| Symmetry | Electronic Energy (Hartree) |
Vibronic Energy (Hartree) |
Nature |
|---|---|---|---|
| Cs CORINA | -233.282,026 | -233.130,937 | global minimum |
| Cs | -233.280,442 | -233.129,881 | saddle point |
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