Structural Characterization of Aromatic−Aromatic Complexes by Rotational Coherence Spectroscopy (original) (raw)
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Chemical Physics Letters, 1992
Rotational coherence spectroscopy has been used to measure rotational constants of the perprotonated and perdeuterated isotopomers of perylene-Ar, two isomers of perylene-(Ar) 2, perylene-Ne, and perylene-(Ne) 2. A structural analysis of the various species has been performed based on these results. A comparison of the geometries so obtained with those proposed by others based on potential energy calculations and vibronic frequency shifts confirms the validity of the latter approach for perylene-(rare gas), species.
Investigation of molecular van der Waals complexes with perylene and tetracene in the molecular beam
The Journal of Physical Chemistry, 1990
Molecular van der Waals (vdW) complexes A-M, of A = perylene (Per) and tetramne (Tet) and M = benzene (B), cyclohexane, and CCll were studied by using the technique of two-color resonant ionization (2CRI) spectroscopy. The investigations included large complexes up to n = 7. The red spectral shifts of the origins of the complexes relative to the bare parent molecules and spectral features of conformational vdW isomers were determined. It was found that the origin of the Tet-B, complex is blue-shifted with respect to Tet-B,. This unusual behavior is tentatively explained by assuming a specific interaction of the two benzene molecules adsorbed on one side of the tetracene molecular plane in a T-shape geometry. The red spectral shifts of Per.B, and Tet.B, complexes exhibit a saturation for n = 5-7 at ca. 700 cm-l which corresponds to ca. 50% of the solvent red spectral shift observed in benzene solutions. In analogy to atomic complexation, it is therefore suggested that a "first solvent shell" consists of 5-7 benzene molecules for vdW complexes of perylene and tetracene.
Physical Chemistry Chemical Physics, 2013
The rotational spectra for the normal isotopic species and for six 13 C singly substituted isotopologues (in natural abundance) of the fluorobenzeneÁ Á Áacetylene (C 6 H 5 FÁ Á ÁHCCH) weakly bound dimer have been measured in the 6.5-18.5 GHz region using chirped-pulse Fourier-transform microwave spectroscopy. The HCCH molecule interacts with the fluorobenzene via a CHÁ Á Áp contact and is determined to lie almost over the center of, and approximately perpendicular to, the aromatic ring, with an HÁ Á Áp distance (perpendicular distance from the H atom to the ring plane) of around 2.492(47) Å; a slight tilt of HCCH towards the para carbon atom of the fluorobenzene is evident. Binding energies of this complex and related benzene and fluorobenzene dimers obtained from the pseudodiatomic approximation are compared and indicate that fluorobenzeneÁ Á Áacetylene lies among the more weakly bound of the complexes exhibiting some type of CHÁ Á Áp interaction.
Rotationally resolved electronic spectroscopy of the rotamers of 1,3-dimethoxybenzene
Physical Chemistry Chemical Physics, 2017
Conformational assignments in molecular beam experiments are often based on relative energies, although there are many other relevant parameters, such as conformer-dependent oscillator strengths, Franck-Condon factors, quantum yields and vibronic couplings. In the present contribution, we investigate the conformational landscape of 1,3-dimethoxybenzene using a combination of rotationally resolved electronic spectroscopy and high level ab initio calculations. The electronic origin of one of the three possible planar rotamers (rotamer (0,180) with both substituents pointing at each other) has not been found. Based on the calculated potential energy surface of 1,3-dimethoxybenzene in the electronic ground and lowest excited state, we show that this can be explained by a distorted non-planar geometry of rotamer (0,180) in the S 1 state.
High-resolution infrared spectroscopy of naphthalene and acenaphthene dimers
Molecular Physics, 2020
Non-covalent interactions are rapidly gaining interest as they are often crucial in determining the properties of materials, and key to supramolecular chemistry and to biochemistry. Non-covalent Polycyclic Aromatic Hydrocarbon (PAH) complexes are in particular relevant to astrochemistry and combustion chemistry where they are involved in the initial steps of condensation and soot formation, respectively. Here, we investigated non-covalent π-π stacking and CH-π interactions in naphthalene and acenaphthene clusters using high-resolution IR-UV spectroscopy in combination with quantum chemical calculations. We identified spectral shifts that occur upon complexation and thereby evaluated predicted potential energy surfaces. Although theory predicts a blueshift, a redshift is observed for the aliphatic CH-π interactions in the experimental spectrum of acenaphthene upon dimerization, indicating that CH-π interaction indeed affects the aliphatic bonds, while a blueshift is predicted, consequently theory deserves attention here. The results provide strong indications for a prevalent parallel naphthalene dimer, showing that π-π stacking interactions become significant for bicyclic and larger PAHs.