Vibrational energy relaxation of benzene dimer and trimer in the CH stretching region studied by picosecond time-resolved IR-UV pump-probe spectroscopy

A structural study on the excimer state of an isolated benzene dimer using infrared spectroscopy in the skeletal vibration region

IR spectroscopy on an isolated benzene excimer reveals that both the electronic and vibrational excitations are in resonance.

Low-energy structures of benzene clusters with a novel accurate potential surface

The benzene-benzene (Bz-Bz) interaction is present in several chemical systems and it is known to be crucial in understanding the specificity of important biological phenomena. In this work, we propose a novel Bz-Bz analytical potential energy surface which is fine-tuned on accurate ab initio calculations in order to improve its reliability. Once the Bz-Bz interaction is modeled, an analytical function for the energy of the Bzn clusters may be obtained by summing up over all pair potentials. We apply an evolutionary algorithm (EA) to discover the lowest-energy structures of Bzn clusters (for n=2-25), and the results are compared with previous global optimization studies where different potential functions were employed. Besides the global minimum, the EA also gives the structures of other low-lying isomers ranked by the corresponding energy. Additional ab initio calculations are carried out for the low-lying isomers of Bz3 and Bz4 clusters, and the global minimum is confirmed as the most stable structure for both sizes. Finally, a detailed analysis of the low-energy isomers of the n = 13 and 19 magic-number clusters is performed. The two lowest-energy Bz13 isomers show S6 and C3 symmetry, respectively, which is compatible with the experimental results available in the literature. The Bz19 structures reported here are all non-symmetric, showing two central Bz molecules surrounded by 12 nearest-neighbor monomers in the case of the five lowest-energy structures.

Theoretical study of nascent solvation in Ni+ (benzene)m, m = 3 and 4, clusters

The ligand versus solvent behavior of Ni(+)(C6H6)3,4 complexes was studied using density functional theory all-electron calculations. Dispersion corrections were included with the BPW91-D2 method using the 6-311++G(2d,2p) basis set. The ground state (GS) for Ni(+)(C6H6)3 has three benzene rings 3d-π bonded to the metal. A two-layer isomer with two moieties coordinated η(3)-η(2) with Ni(+), and the other one adsorbed by van der Waals interactions to the Ni(+)(C6H6)2 subcluster, i.e., a 2 + 1 structure, is within about 8.4 kJ/mol of the GS. Structures with 3 + 1 and 2 + 2 ligand coordination were found for Ni(+)(C6H6)4. The binding energies (D0) of 28.9 and 26.0 kJ/mol for the external moieties of Ni(+)(C6H6)3,4 are much smaller than that for Ni(+)(C6H6)2, 193.0 kJ/mol, obtained also with BPW91-D2. This last D0 overestimates somehow the experimental value, of 146.7 ± 11.6 kJ/mol, for Ni(+)(C6H6)2. The abrupt fall for D0(Ni(+)(C6H6)3,4) shows that such molecules are bound externally as solvent species. These results agree with the D0(Ni(+)(C6H6)3) < 37.1 kJ/mol limit found experimentally for this kind of two-layer clusters. The ionization energies also decrease for m = 2, 3, and 4 (580.8, 573.1, and 558.6 kJ/mol). For Ni(+)(C6H6)3,4, each solvent moiety bridges the benzenes of Ni(+)(C6H6)2; their position and that of one internal ring mimics the tilted T-shape geometry of the benzene dimer (Bz2). The distances from the center of the external to the center of the internal rings for m = 3 (4.686 Å) and m = 4 (4.523 Å) are shorter than that for Bz2 (4.850 Å). This and charge transfer effects promote the (C(δ-)-H(δ+))(int) dipole-π(ext) interactions in Ni(+)(C6H6)3,4; π-π interactions also occur. The predicted IR spectra, having multiplet structure in the C-H region, provide insight into the experimental spectra of these ions.