Ground state for CH₂ and symmetry for methane decomposition

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.