The structure and dipole moment of the argon·fluorobenzene dimer

The millimeter-wave rotational spectrum of fluorobenzene

“…The parent and eight isotopically substituted isotopomers have been investigated [5][6][7], resulting in the determination of the r s [6], and of the r 0 geometry [8]. The dipole moment of fluorobenzene, l = 1.555(3) D has also been measured during a study of the fluorobenzene-Ar dimer [9], and normal coordinate analysis of the vibrational spectrum has been carried out [10]. It is of interest that the current knowledge of the rotational spectrum in the lowest excited vibrational states comes from pulsed-jet Fourier transform microwave (FTMW) spectroscopy [11], which is not normally considered to be a useful tool for such studies.…”

Two-dimensional laser induced fluorescence spectroscopy of van der Waals complexes: Fluorobenzene-Arn (n = 1,2)

“…In the absence of data from isotopically substituted species, experiment is unable to differentiate between the Ar being displaced from the FB CoM towards or away from the C-F bond. Isotopic substitution experiments 8 and ab initio calculations 2,3 have established that the Ar is displaced from the FB CoM towards the centre of the ring in S 0 . Ab initio calculations show that the displacement is also in this direction in S 1 .…”

“…For each electronic state the calculations provide a number of predictions, including the van der Waals vibrational states in the lower region of the vibrational manifold, the molecular geometry and the binding energy. Currently, experimental data are available concerning the S 0 and S 1 binding energies, 5,6 the S 0 rotational constants, 7,8 and hence S 0 geometry, and a number of the S 1 van der Waals vibrational levels. 5,6,[9][10][11] However, the S 1 rotational constants, and hence the S 1 geometry for the complex, have yet to be satisfactorily determined 4 and, with the exception of the two bend fundamentals, 12 the S 0 van der Waals vibrational level structure remains unobserved.…”

“…The ground state geometry of the complex has been inferred from the known FB geometry and the FB-Ar rotational constants determined using microwave studies. 7,8 Two structures satisfy the rotational constants. These differ in the direction of displacement of the Ar atom from the FB centre of mass (CoM), with Ar being either towards the C-F bond or towards the centre of the ring.…”

“…A study using isotopically substituted samples has shown that the correct structure has the Ar displaced towards the centre of the ring and away from the C-F bond. 8 Vibrational frequencies of the two van der Waals bending vibrations in S 0 have been determined using stimulated Raman spectroscopy. 12 Regarding the S 1 state of the FB-Ar complex, as is usual with aromatic-rare gas complexes the dispersion interaction is stronger in the excited electronic state, resulting in the S 1 -S 0 origin transition being red shifted by 24 cm −1 compared with the monomer.…”