Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states
The potential energy surfaces of the van der Waals complexes benzene–Ar and p-difluorobenzene–Ar have been investigated at the second-order Møller–Plesset (MP2) level of theory with the aug-cc-pVDZ basis set. Calculations were performed with unconstrained geometry optimization for all stationary poi...
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| Format: | Journal Article |
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American Institute of Physics
2004
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| Online Access: | http://hdl.handle.net/20.500.11937/26042 |
| _version_ | 1848751873453981696 |
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| author | Moulds, R. Buntine, Mark Lawrance, W. |
| author_facet | Moulds, R. Buntine, Mark Lawrance, W. |
| author_sort | Moulds, R. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | The potential energy surfaces of the van der Waals complexes benzene–Ar and p-difluorobenzene–Ar have been investigated at the second-order Møller–Plesset (MP2) level of theory with the aug-cc-pVDZ basis set. Calculations were performed with unconstrained geometry optimization for all stationary points. This study has been performed to elucidate the nature of a conflict between experimental results from dispersed fluorescence and velocity map imaging (VMI). The inconsistency is that spectra for levels of p-difluorobenzene–Ar and –Kr below the dissociation thresholds determined by VMI show bands where free p-difluorobenzene emits, suggesting that dissociation is occurring. We proposed that the bands observed in the dispersed fluorescence spectra are due to emission from states in which the rare gas atom orbits the aromatic chromophore; these states are populated by intramolecular vibrational redistribution from the initially excited level [S. M. Bellm, R. J. Moulds, and W. D. Lawrance, J. Chem. Phys. 115, 10709 (2001)]. To test this proposition, stationary points have been located on both the benzene–Ar and p-difluorobenzene–Ar potential energy surfaces (PESs) to determine the barriers to this orbiting motion. Comparison with previous single point CCSD(T) calculations of the benzene–Ar PES has been used to determine the amount by which the barriers are overestimated at the MP2 level.As there is little difference in the comparable regions of the benzene–Ar and p-difluorobenzene–Ar PESs, the overestimation is expected to be similar for p-difluorobenzene–Ar. Allowing for this overestimation gives the barrier to movement of the Ar atom around the pDFB ring via the valley between the H atoms as ⩽204 cm−1 in S0 (including zero point energy). From the estimated change upon electronic excitation, the corresponding barrier in S1 is estimated to be ⩽225 cm−1. This barrier is less than the 240 cm−1 energy of30 2, the vibrational level for which the anomalous “free p-difluorobenzene” bands were observed in dispersed fluorescence from p-difluorobenzene–Ar, supporting our hypothesis for the origin of these bands. |
| first_indexed | 2025-11-14T07:59:39Z |
| format | Journal Article |
| id | curtin-20.500.11937-26042 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T07:59:39Z |
| publishDate | 2004 |
| publisher | American Institute of Physics |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-260422018-03-29T09:08:13Z Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states Moulds, R. Buntine, Mark Lawrance, W. Fluorescence Der-Waals complexes Fluorobenzene Spectrum Dissociation-energy Ionization Dynamics Dipole-moment Argon Vanderwaals complex The potential energy surfaces of the van der Waals complexes benzene–Ar and p-difluorobenzene–Ar have been investigated at the second-order Møller–Plesset (MP2) level of theory with the aug-cc-pVDZ basis set. Calculations were performed with unconstrained geometry optimization for all stationary points. This study has been performed to elucidate the nature of a conflict between experimental results from dispersed fluorescence and velocity map imaging (VMI). The inconsistency is that spectra for levels of p-difluorobenzene–Ar and –Kr below the dissociation thresholds determined by VMI show bands where free p-difluorobenzene emits, suggesting that dissociation is occurring. We proposed that the bands observed in the dispersed fluorescence spectra are due to emission from states in which the rare gas atom orbits the aromatic chromophore; these states are populated by intramolecular vibrational redistribution from the initially excited level [S. M. Bellm, R. J. Moulds, and W. D. Lawrance, J. Chem. Phys. 115, 10709 (2001)]. To test this proposition, stationary points have been located on both the benzene–Ar and p-difluorobenzene–Ar potential energy surfaces (PESs) to determine the barriers to this orbiting motion. Comparison with previous single point CCSD(T) calculations of the benzene–Ar PES has been used to determine the amount by which the barriers are overestimated at the MP2 level.As there is little difference in the comparable regions of the benzene–Ar and p-difluorobenzene–Ar PESs, the overestimation is expected to be similar for p-difluorobenzene–Ar. Allowing for this overestimation gives the barrier to movement of the Ar atom around the pDFB ring via the valley between the H atoms as ⩽204 cm−1 in S0 (including zero point energy). From the estimated change upon electronic excitation, the corresponding barrier in S1 is estimated to be ⩽225 cm−1. This barrier is less than the 240 cm−1 energy of30 2, the vibrational level for which the anomalous “free p-difluorobenzene” bands were observed in dispersed fluorescence from p-difluorobenzene–Ar, supporting our hypothesis for the origin of these bands. 2004 Journal Article http://hdl.handle.net/20.500.11937/26042 10.1063/1.1772355 American Institute of Physics restricted |
| spellingShingle | Fluorescence Der-Waals complexes Fluorobenzene Spectrum Dissociation-energy Ionization Dynamics Dipole-moment Argon Vanderwaals complex Moulds, R. Buntine, Mark Lawrance, W. Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title | Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title_full | Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title_fullStr | Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title_full_unstemmed | Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title_short | Ab initio calculations of stationary points on the benzene-Ar and p-difluorobenzene-Ar potential energy surfaces: barriers to bound orbiting states |
| title_sort | ab initio calculations of stationary points on the benzene-ar and p-difluorobenzene-ar potential energy surfaces: barriers to bound orbiting states |
| topic | Fluorescence Der-Waals complexes Fluorobenzene Spectrum Dissociation-energy Ionization Dynamics Dipole-moment Argon Vanderwaals complex |
| url | http://hdl.handle.net/20.500.11937/26042 |