Graduate student Katelyn Dreux will present “Exploring the Potential Energy Surface of the H₂O∙∙∙O₂ van der Waals complex” to the department.

Abstract:

Over the past two decades, numerous studies into atmospheric interactions have been conducted as a result of increasing interest in a variety of areas, including solar radiation, greenhouse gases, and cloud formation. Water and oxygen are both present and highly abundant in the troposphere, making this an important complex for study. The H­₂O^…O₂ dimer is of particular interest because of its potential viability as a greenhouse gas. Water’s role in the Earth’s radiation budget is well defined, as it can absorb IR radiation from the Earth.¹ O₂ is IR inactive, but upon dimerization with water, changes in frequency and intensity may occur. The intermolecular modes that result from such an association with large intensities could indicate the complex’s ability to absorb IR radiation.¹  Results will be presented from a series of full geometry optimizations and harmonic vibrational frequency computations performed at the UCCSD(T) level using Dunning’s correlation consistent basis sets with diffuse functions on every atom but hydrogen (haXZ, where X = D,T,Q). Seven different structures were considered, six C_2v structures, four planar and two non-planar, and one with C_s symmetry. The C_s structure has an electronic binding energy of -0.70 kcal mol^-1 and is the global minimum at the UCCSD(T)/haQZ level of theory. Binding energies for the C_2v structures range from -0.26 to -0.59 kcal mol^-1, highlighting the very shallow nature of the potential energy surface. Analysis of the vibrational frequencies indicates that the formation of the H₂O^…O₂ complex produces two low energy intermolecular modes under 100 cm^-1 with large IR activities. A similar work studied the interaction of H₂O^…N₂, which is more strongly bound but experiences no significantly enhanced IR activity.³

References:

¹ Svishchev, I.; Boyd, R. J. Chem. Phys. A.102, 7294(1998).
² Sabu, A.; Kondo, S.; Miura, N.; Hashimoto, K. Chem. Phys.Lett. 391, 101(2004).
³ Ellington, Thomas L.; Tschumper, Gregory S. Comput. Theor. Chem.1021,109(2013).