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 X^-3B1 with C2v group for CH2. 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 X^-3∑^-g for the ground state of CH2 in reference. Based on the atomic and molecular reaction statics, this paper proves that the decomposition type （1） i.e. CH4 →CH2＋H2, is forbidden and the decomposition type （2） i.e. CH4→CHa＋H is allowed for CH4. This is similar to the decomposition of SiH4.
The radiation effect of neutrons in a reactor on polyurethane was studied.The gases produced by irradiated samples were analyzed by gas chromatography,and the dynamic mechanical and compression properties of the samples were also studied.The positron annihilation lifetime of irradiated samples was measured at room temperature in vacuum.The experimental results indicate that gas chromatography is a powerful tool to quantitatively analyze the gas products from neutron-irradiated polyurethane and characterizes the chemical changes in the sample.And the changes in microstructure determined from the PAL correlate well with the measurements of the mechanical properties by dynamic mechanical analysis（DMA）.
