Ab initio and DFT study of the molecular conformations and the thermochemistry of the CH2=CHC(O)OONO2 (APAN) atmospheric molecule and of the CH2=CHC(O)OO and CH2=CHC(O)O radicals

MARÍA P. BADENES; CARLOS J. COBOS

JOURNAL OF MOLECULAR STRUCTURE THEOCHEM

Elsevier

Año: 2007 vol. 814 p. 51 - 60

0166-1280

The molecular structures and conformational mobilities of the atmospheric peroxyacryloyl nitrate, CH2=CHC(O)OONO2 (APAN) molecule and its radical decomposition products CH2=CHC(O)OO and CH2=CHC(O)O were studied by ab initio and density functional methods. The potential energy curves for the internal rotations were calculated using the B3LYP hybrid functional with the 6-311++G(d,p) basis set. The equilibrium conformation of APAN, determined at B3LYP/6-311++G(3df,3pd) level, is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in almost perpendicular planes, t(COON) = 86.4º. A quantum statistical analysis showed that only a 7% of the internal rotors of the above molecules can freely rotate at room temperature. From isodesmic energies calculated at the G3MP2//B3LYP/6-311++G(3df,3pd) level of theory, standard enthalpies of formation at 298 K for APAN, CH2=CHC(O)OO and CH2=CHC(O)O are predicted to be -34.8, -8.9, and -16.0 kcal mol-1. The resulting O-N and O-O bond dissociation enthalpies for the channels CH2=CHC(O)OONO2 ® CH2=CHC(O)OO + NO2 and CH2=CHC(O)OONO2 ® CH2=CHC(O)O + NO3 of 34.1 and 36.4 kcal mol-1 are significant larger than those reported for similar processes of the atmospherically relevant PAN species.