PROPYLBENZENE-(H_2O)n Clusters: Effect of the Alkyl Chain on the π H-Bond
Abstract
This talk focuses on the mass resolved- resonant 2-photon ionization (R2PI), resonant ion-dip infrared spectroscopy (RIDIR) and IR-UV holeburning (IR-UV HB) spectroscopy of propylbenzene(pBz)-(H_2O)n clusters and the comparison with their Benzene(Bz)-(H_2O)n cluster counterparts, which are a well-studied prototype system for the π H-bond. Since the pBz monomer exists in gauche and trans conformers, one anticipates the presence of pBz-H_2O complexes with H_2O on the same or opposite sides of the ring as the gauche or trans propyl chain. Indeed, local minima associated with these four complexes were identified by dispersion-corrected DFT calculations. R2PI and IR-UV HB spectra of pBz-H_2O show long Franck-Condon progressions associated with the set of conformers of the complex. The OH stretch RIDIR spectra consist of a single transition in the symmetric stretch region, and a doublet with varying spacing in the antisymmetric stretch region, indicating coupling to a large-amplitude motion (LAM). The changes in the OH stretch region indicate that the water molecule bound to propylbenzene undergoes more restricted motion on the π cloud than its Bz-H_2O counterpart. The potential energy surface for H_2O tumbling on the pBz π cloud was mapped out, and used as the basis for calculating from first principles the OH stretch infrared spectrum. Comparison with the spectrum for Bz-H_2O further illustrates the source and restrictions of the LAM of H_2O in pBz compared to Bz. OH stretch IR spectra of the higher water clusters pBz-(H_2O)n with n=3, 4 are very similar to their Bz-(H_2O)n counterparts, existing as H-bonded cycles, with no evidence of LAM on the aromatic π cloud.
- Publication:
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73rd International Symposium on Molecular Spectroscopy
- Pub Date:
- June 2018
- DOI:
- 10.15278/isms.2018.TE09
- Bibcode:
- 2018isms.confETE09M
- Keywords:
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- Clusters/Complexes