### Abstract

We report a combined experimental and theoretical study of the intermolecular vibrations and van der Waals isomerism of the 2,3-dimethylnaphthalene-He van der Waals complex. Two-color resonant two-photon ionization spectra of the S_{0}→S_{1} electronic transition of 2,3-dimethylnaphthalene-He exhibit five bands within 30 cm ^{-1} of the electronic origin. The intermolecular potential energy surface was modeled as a sum of atom-atom Lennard-Jones pair potentials; it exhibits two equivalent global minima on each side of the naphthalene moiety, and a single shallower local minimum adjacent to the two methyl groups. Based on this surface, accurate three-dimensional quantum calculations of the van der Waals vibrational levels using the discrete variable representation method were performed. Careful optimization of the potential parameters lead to a quantitative reproduction of four observed bands as intermolecular vibrational excitations, a vibrationally averaged He atom distance from the aromatic plane 〈z_{0}〉 = 3.22 Å, and a dissociation energy D_{0}(S_{1})= -60.3 cm ^{-1}, compatible with experiments. The fifth band is assigned as a van der Waals isomer, corresponding to the local minimum. The quantum calculations were extended up to the dissociation limit, yielding ≈ 173 van der Waals vibrational states. Above 70% of D_{0}, many vibrational states are completely delocalized over the potential surface, with root-mean-square vibrational amplitudes up to 6 A parallel to and up to 1.5 A perpendicular to the molecular surface. Calculated tunnelling splittings range from < 10 ^{-4} cm ^{-1} for localized states, to >3 cm ^{-1} for highly delocalized ones.

Original language | English (US) |
---|---|

Pages (from-to) | 8781-8793 |

Number of pages | 13 |

Journal | Journal of Chemical Physics |

Volume | 107 |

Issue number | 21 |

State | Published - Dec 1 1997 |

### Fingerprint

### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

*Journal of Chemical Physics*,

*107*(21), 8781-8793.

**Very large amplitude intermolecular vibrations and wave function delocalization in 2,3-dimethylnaphthalene · He van der Waals complex.** / Bach, Andreas; Leutwyler, Samuel; Sabo, Dubravko; Bacic, Zlatko.

Research output: Contribution to journal › Article

*Journal of Chemical Physics*, vol. 107, no. 21, pp. 8781-8793.

}

TY - JOUR

T1 - Very large amplitude intermolecular vibrations and wave function delocalization in 2,3-dimethylnaphthalene · He van der Waals complex

AU - Bach, Andreas

AU - Leutwyler, Samuel

AU - Sabo, Dubravko

AU - Bacic, Zlatko

PY - 1997/12/1

Y1 - 1997/12/1

N2 - We report a combined experimental and theoretical study of the intermolecular vibrations and van der Waals isomerism of the 2,3-dimethylnaphthalene-He van der Waals complex. Two-color resonant two-photon ionization spectra of the S0→S1 electronic transition of 2,3-dimethylnaphthalene-He exhibit five bands within 30 cm -1 of the electronic origin. The intermolecular potential energy surface was modeled as a sum of atom-atom Lennard-Jones pair potentials; it exhibits two equivalent global minima on each side of the naphthalene moiety, and a single shallower local minimum adjacent to the two methyl groups. Based on this surface, accurate three-dimensional quantum calculations of the van der Waals vibrational levels using the discrete variable representation method were performed. Careful optimization of the potential parameters lead to a quantitative reproduction of four observed bands as intermolecular vibrational excitations, a vibrationally averaged He atom distance from the aromatic plane 〈z0〉 = 3.22 Å, and a dissociation energy D0(S1)= -60.3 cm -1, compatible with experiments. The fifth band is assigned as a van der Waals isomer, corresponding to the local minimum. The quantum calculations were extended up to the dissociation limit, yielding ≈ 173 van der Waals vibrational states. Above 70% of D0, many vibrational states are completely delocalized over the potential surface, with root-mean-square vibrational amplitudes up to 6 A parallel to and up to 1.5 A perpendicular to the molecular surface. Calculated tunnelling splittings range from < 10 -4 cm -1 for localized states, to >3 cm -1 for highly delocalized ones.

AB - We report a combined experimental and theoretical study of the intermolecular vibrations and van der Waals isomerism of the 2,3-dimethylnaphthalene-He van der Waals complex. Two-color resonant two-photon ionization spectra of the S0→S1 electronic transition of 2,3-dimethylnaphthalene-He exhibit five bands within 30 cm -1 of the electronic origin. The intermolecular potential energy surface was modeled as a sum of atom-atom Lennard-Jones pair potentials; it exhibits two equivalent global minima on each side of the naphthalene moiety, and a single shallower local minimum adjacent to the two methyl groups. Based on this surface, accurate three-dimensional quantum calculations of the van der Waals vibrational levels using the discrete variable representation method were performed. Careful optimization of the potential parameters lead to a quantitative reproduction of four observed bands as intermolecular vibrational excitations, a vibrationally averaged He atom distance from the aromatic plane 〈z0〉 = 3.22 Å, and a dissociation energy D0(S1)= -60.3 cm -1, compatible with experiments. The fifth band is assigned as a van der Waals isomer, corresponding to the local minimum. The quantum calculations were extended up to the dissociation limit, yielding ≈ 173 van der Waals vibrational states. Above 70% of D0, many vibrational states are completely delocalized over the potential surface, with root-mean-square vibrational amplitudes up to 6 A parallel to and up to 1.5 A perpendicular to the molecular surface. Calculated tunnelling splittings range from < 10 -4 cm -1 for localized states, to >3 cm -1 for highly delocalized ones.

UR - http://www.scopus.com/inward/record.url?scp=0001344437&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0001344437&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0001344437

VL - 107

SP - 8781

EP - 8793

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 21

ER -