Thermodynamical stability of CH3ONO and CH3ONO-: A coupled-cluster and Hartree-Fock-density-functional-theory study

The structure and thermodynamic stability of methylnitrite and its anion ar e studied by the infinite-order coupled-cluster method with all singles and doubles and noniterative inclusion of triple excitations [CCSD(T)] and Har tree-Fock-density-functional theory (HFDFT). We have optimized the geometri es and computed the harmonic vibrational frequencies of major fragments, H- 2, CH, NH, OH, CN, N-2, CO, NO, O-2, CH2, NH2, H2O, HCN, HNC, HCO, HNO, O2H , CO2, NO2, CH3, NH3, CNH2, HCO2, HNO2, CH3N, CH3O, CH3NO, CH3ON, CH2NO2, a nd their anions, when the latter exist. Fragmentation energies obtained at both levels of theory are rather close to each other, except for channels i nvolving CN as a product. The CH3ONO- and CH3NO2- anions are shown to posse ss lower fragmentation energies than their neutral parents. This implies th at the attachment of an extra electron to CH3NO2 or CH3ONO may have a cruci al role in initiating the decomposition of these compounds. Also, the attac hment of an extra electron to CH3NO2 or CH3ONO leads to the appearance of n ew exothermic decay channels of the anions. (C) 1999 American Institute of Physics. [S0021-9606(99)30801-1].