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"High Resolution Spectroscopy as a Probe of the Fundamental Nature of Prototypical Non-covalent Interactions"

John W. Bevan
Department of Chemistry
Texas A&M University


Although intermolecular bonding between molecules is much weaker than bonding in normal covalent molecules, such interactions are pervasive and determine countless properties in all phases of matter. The influence of large amplitude, highly anharmonic motions complicate concerted experimental studies even in small systems.

Precise measurement of transitions corresponding to discrete absorptions have been used as the experimental data to be inputted into the CMM computational model for accurately predicting properties of intermolecular interactions. Technological developments in the infrared and submillimeter/terahertz spectral regions have given unique opportunities for such experimental investigations. This experimental data was generated using state-of-the-art techniques exploiting recently developed quantum cascade lasers and ultra-high resolution THz techniques developed in house.

The synergistic approach of combining experiment with morphing methodologies has been demonstrated in the ground state structure of (HI)2 to give rise to an unexpected symmetric paired hydrogen bonded structure unlike any other (HX)2 (X=F, Cl, Br) dimer. Furthermore, morphing methodologies have been used to predict an anomalous deuterium isotope effect in the ground state isotopic isomerization of OC-HI. Here, the ground state hydrogen H-bonded structure of OC-HI contrasts with the corresponding ground state van der Waals OC-ID structure, a fundamental phenomenon not considered before in non-covalent interactions. More recently, a CMM-RS methodology has been further refined for all vibrations in OC-HF. This potential was morphed using only a four parameter fit to near experimental accuracy with primary analyzed rotational and vibrational parameters within 0.001%. Such studies have also been generalized to halogen bonds including OC-Cl2, OC-BrCl and OC-Br2. The investigation of OC-Cl2 permitted detailed comparison of its structure and molecular motion with OC-HCl which has equivalent binding energy. Recently, we have been able to correlate the predictions of binding energies based on CMM approaches with blue frequency shifts of the hydrogen acceptor CO on complexation in the H bonded series OC-HX (X=F, Cl, Br, I, CN, CCH) consistent with the original tenets of a rule initially proposed by Badger-Bauer in 1937. This acts as a calibration curve for accurately predicting binding energies of other complexes without the necessity of detailed experimental investigation or complete morphing calculations.

Friday, October 12, 2012
IQSE 578, 2:00 p.m.
Mitchell Physics Building

Department of Physics and Astronomy
Texas A&M University

(Coffee and Cookies to be served 1:45 p.m.)