10min:

T. J. DHILIP KUMAR, Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48105; JOHN F. STANTON, Institute for Theoretical Chemistry, Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712; AND JOHN R. BARKER, Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48105.

The important atmospheric reactions HO₂ + NO and OH + NO₂ lead to formation and dissociation of the cis- and trans- isomers of the HOONO complex. In the present work, the global HNO₃ potential energy surface (PES) is being studied by using high-level ab initio electronic structure methods. This PES and others in the same class have been studied previously by others. In the F + NO₂ reaction system, UCCSD(T) calculations showed that FONO isomerizes to FNO₂ through a tight transition state involving a two-state avoided curve crossing. A similar mechanism has been invoked for HOONO, which is isoelectronic with FONO. CASSCF multi-configurational calculations on the CH₃O + NO₂ reaction located a conical intersection near where single-configurational DFT methods predict an intrinsic energy barrier; the barrier was suggested to be an artifact. In present work, the global HNO₃ PES is being investigated by both the UCCSD(T) and CASSCF methods in order to study the influence of low-lying excited electronic states on the ground state PES and reaction dynamics.