Binding energy of the styrene-argon van der Waals molecule

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.

Identification of impurities in phenylacetylene by species-selected mass-analyzed threshold ionization spectroscopy

Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to identify styrene impurities in a commercial phenylacetylene sample. With the mass-gating setup, the recorded MATI spectra are free of contamination from molecules of different mass. Analysis of these spectra gives information on the precise adiabatic ionization and the active cation vibrations, which can be used as fingerprints for the identification of molecular ions.