A ground state morphed intermolecular potential for the hydrogen bonded and van der Waals isomers in OC:HI and a prediction of an anomalous deuterium isotope effect.
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abstract
An extended analysis of the noncovalent interaction OC:HI is reported using microwave and infrared supersonic jet spectroscopic techniques. All available spectroscopic data then provide the basis for generating an accurately determined vibrationally complete semiempirical intermolecular potential function using a four-dimensional potential coordinate morphing methodology. These results are consistent with the existence of four bound isomers: OC-HI, OC-IH, CO-HI, and CO-IH. Analysis also leads to unequivocal characterization of the common isotopic ground state as having the OC-HI structure and with the first excited state having the OC-IH structure with an energy of 3.4683(80) cm(-1) above the ground state. The potential is consistent with the following barriers between the pairs of isomers: 382(4) cm(-1) (OC-IH/OC-HI), 294(5) cm(-1) (CO-IH/CO-HI), 324(3) cm(-1) (OC-IH/CO-IH), and 301(2) cm(-1) (OC-HI/CO-HI) defined with respect to each lower minimum. The potential is also determined to have a linear OC-IH van der Waals global equilibrium minimum structure having R(e)=4.180(11) , (1)=0.00(1), and (2)=0.00(1). This is differentiated from its OC-HI ground state hydrogen bound structure having R(0)=4.895(1) , (1)=20.48(1), and (2)=155.213(1) where the distances are defined between the centers of mass of the monomers and (1) and (2) as cos(-1)[(1/2)] for i=1 and 2. A fundamentally new molecular phenomenon - ground state isotopic isomerization is proposed based on the generated semiempirical potential. The protonated ground state hydrogen-bonded OC-HI structure is predicted to be converted on deuteration to the corresponding ground state van der Waals OC-ID isomeric structure. This results in a large anomalous isotope effect in which the R(0) center of mass distance between monomeric components changes from 4.895(1) to 4.286(1) . Such a proposed isotopic effect is demonstrated to be a consequence of differential zero point energy factors resulting from the shallower nature of hydrogen bonding at a local potential minimum (greater quartic character of the potential) relative to the corresponding van der Waals global minimum. Further consequences of this anomalous deuterium isotope effect are also discussed.
Rivera-Rivera, L. A., Wang, Z., McElmurry, B. A., Willaert, F. F., Lucchese, R. R., Bevan, J. W., Suenram, R. D., & Lovas, F. J.
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Rivera-Rivera, Luis A||Wang, Zhongcheng||McElmurry, Blake A||Willaert, Fabrice F||Lucchese, Robert R||Bevan, John W||Suenram, Richard D||Lovas, Frank J
