High-resolution ultraviolet spectroscopy of p-fluorostyrene-water: Evidence for a σ-type hydrogen-bonded dimer

Van der Waals Bonding to a Molecule with π-Electron Conjugation: Styrene-Argon Complex Studied by Mass Selective High Resolution R2PI UV Spectroscopy and Ab-initio Calculations

Combining high-resolution mass-selective resonance-enhanced two-photon ionization spectroscopy analysed by genetic-algorithm-based computer-assisted rotational fit and high-level ab initio calculations we were able to determine the structure and the transition moment orientation of the styrene-Ar complex. The results demonstrate that Ar binds to the benzene ring of styrene. The binding site of Ar is 3.42 Å above the benzene-ring plane and is close to the C 6 symmetry axis of the aromatic ring, but slightly shifted to the vinyl group, which implies that the binding pattern is perturbed by the presence of the bonded to the benzene ring vinyl group. The transition moment ratio of the styrene-Ar complex is considerably different from the one of bare styrene this being a purely mass effect stemming from the reorientation of the principal axes of inertia upon the cluster formation. The red shift of the 00 0 origin band of the styrene-Ar2 complex is almost twice that of the single complex, indicating that the red-shift additivity rule holds in this case. On this basis we conclude that the second Ar atom is bound to the opposite side of the benzene ring.

Evidence for a C–H⋯π type weak interaction: 1 : 1 complex of styrene with acetylene studied by mass selective high-resolution UV spectroscopy and ab initio calculations

The 1 : 1 complex of styrene with acetylene has been studied by mass selective low- and high-resolution UV resonance-enhanced two-photon ionisation (R2PI) spectroscopy combined with genetic-algorithm-based computer-aided fit of the spectra with partial rotational resolution, and high level ab initio quantum chemistry calculations. Two stable conformeric geometries of the 1 : 1 complex of styrene and acetylene have been theoretically found: one with acetylene binding to styrene as a proton donor, and one with acetylene acting as a proton acceptor. From the analysis of the vibronic structure of the S1<-- S0 spectrum and the fit of the highly resolved spectrum of the 0 origin band of the complex it is shown that the favoured conformation is the one in which acetylene binds to the benzene ring of styrene through formation of a non-conventional hydrogen bond of C-H...pi type with no marked change of the transition moment orientation of styrene. The styrene moiety remains planar and the acetylene molecule is tilted by a small angle of 4 degrees relative to the C6 symmetry axis of the benzene ring, most likely due to the reduced symmetry of the benzene ring pi electrons rather than to a direct interaction with the vinyl group.

Specific and nonspecific interactions in a molecule with flexible side chain: 2-phenylethanol and its 1:1 complex with argon studied by high-resolution UV spectroscopy

Using high-resolution resonance-enhanced two-photon ionization spectroscopy in combination with genetic-algorithm-based computer-aided rotational fit analysis and ab initio quantum chemistry calculations we determined the conformational structure and transition moment orientation in 2-phenylethanol and its 1:1 clusters with argon. The results clearly demonstrate that the gauche structure of 2-phenylethanol, which is stabilized by the intramolecular pi-hydrogen bond between the folded side chain and the benzene ring, is the most abundant in the cold molecular beam. In this conformer the transition moment is rotated by 18 degrees from the short axis of the aromatic ring. Two distinct 1:1 complexes of 2-phenylethanol with argon in a cis- and trans-configuration with respect to the side chain have been found. Employing the Kraitchman [Am. J. Phys. 21, 17 (1953)] analysis we have found that the structure of the 2-phenylethanol moiety and the orientation of the transition moment do not change after the complexation with argon within the experimental accuracy. From the measured band intensities we conclude that in addition to the dispersion interaction of the argon atom with the aromatic ring a hydrogen-bond-type interaction with the terminal -OH group of the side chain stabilizes the cis-structure of the 1:1 complex of 2-phenylethanol with argon.

The World of Non-Covalent Interactions: 2006

The review focusses on the fundamental importance of non-covalent interactions in nature by illustrating specific examples from chemistry, physics and the biosciences. Laser spectroscopic methods and both ab initio and molecular modelling procedures used for the study of non-covalent interactions in molecular clusters are briefly outlined. The role of structure and geometry, stabilization energy, potential and free energy surfaces for molecular clusters is extensively discussed in the light of the most advanced ab initio computational results for the CCSD(T) method, extrapolated to the CBS limit. The most important types of non-covalent complexes are classified and several small and medium size non-covalent systems, including H-bonded and improper H-bonded complexes, nucleic acid base pairs, and peptides and proteins are discussed with some detail. Finally, we evaluate the interpretation of experimental results in comparison with state of the art theoretical models: this is illustrated for phenol...Ar, the benzene dimer and nucleic acid base pairs. A review with 270 references.