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74 Poster session, D27Theoretical Investigation of the HOCO radical in the GroundElectronic StateMirjana MladenovićMladenovic M.Universite Paris Est, Laboratoire MSME, UMR8208 CNRS, France,Mirjana.Mladenovic@univ-paris-est.frHydrocarboxyl radical, HOCO, plays an important role in the reaction betweenhydroxyl radical and carbon monoxid, HO+CO→H+CO 2 , which provides the mostcommon pathway for atmospheric depletion of both OH and CO and is the principlesource of heat in hydrocarbon flames. Our primary interest in HOCO arises from thenew spectroscopic information 1 , providing gas phase spectra of the cis-conformer forthe first time. In the present work, the potential energy surface (PES) for HOCO for theground electronic state (X 2 A’) was explored by means of the partially spin adaptedcoupled cluster RCCSD(T) method using the cc-pVQZ basis set. Ab initio calculationswere designed such to cover the range of spectroscopic interest.Vibrational and rovibrational (J=0-4) energy levels are obtained by means ofcomputational strategies based on the discrete variable representation [DVR6] and the(functional+pointwise) coordinate representations [DVR(+R)+FBR] together withcontraction schemes resulting from several diagonalization/truncation steps. 2,3Rotational constants computed for the ground vibrational state of trans-HOCO and cis-HOCO are in good agreement with the experimental values. Several adiabatic projectionschemes have been employed to characterize the vibrational levels and to study therelevance of the intermode coupling (vibrational mixing).Numerically exact vibrational transitions are also presented for the quartic force fieldsdeveloped recently for trans-HOCO, cis-HOCO, and the cis-HOCO anion 4,5 . Our resultshelp to clear up a large discrepancy between previously reported vibrationalperturbation theory (VPT) and vibrational configuration interaction (VCI) predictionsfor the torsional frequency.References[1] T. Oyama, W. Funato, Y. Sumiyoshi, Y. Endo, J. Chem. Phys. 134, 174303, 2011[2] M. Mladenović, J. Chem. Phys. 112, 1070, 2000[3] M. Mladenović, Spectrochim. Acta, Part A, 58, 809, 2002[4] R. C. Fortenberry, X. Huang, J. S. Francisco, T. D. Crawford, T. J. Lee, J. Chem.Phys. 135, 134301, 2011[5] R. C. Fortenberry, X. Huang, J. S. Francisco, T. D. Crawford, T. J. Lee, J. Chem.Phys. 135, 214303, 2011