关键词: symmetry, free radical CH$_{2}$, decomposition of CH$_{4}$

Abstract: Using the different level of methods B3P86, BLYP、B3PW91, HF, QCISD、CASSCF (4,4) and MP2 with the various basis functions 6-311G**, D95, cc--pVTZ and DGDZVP, the calculations of this paper confirm that the ground state is $\tilde {X}{ }^3B_1 $ with $C_{2v} $ group for CH$_{2}$. Furthermore, the three kinds of theoretical methods, i.e. B3P86、CCSD(T, MP4) and G2 with the same basis set cc-pVTZ only are used to recalculate the zero-point energy revision which are modified by scaling factor 0.989 for the high level based on the virial theorem, and also with the correction for basis set superposition error. These results are also contrary to $\tilde {X}{ }^3\varSigma _{\rm g} ^ - $ for the ground state of CH$_{2}$ in reference. Based on the atomic and molecular reaction statics, this paper proves that the decomposition type (1) i.e. CH$_{4}\to $CH$_{2}$+H$_{2}$, is forbidden and the decomposition type (2) i.e. CH$_{4} \to $CH$_{3}$+H is allowed for CH$_{4}$. This is similar to the decomposition of SiH$_{4}$.

Key words: symmetry, free radical CH$_{2}$, decomposition of CH$_{4}$