Global potential energy surface of the dissociations of ground- state methylene(CH2)

• Main Authors: Chen, Shu Ying, 陳淑瑩
• Other Authors: Yu, Chin Hui
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/37419819340082966260

碩士 === 國立清華大學 === 化學學系 === 83 === The global potential energy surface of ground-state CH2 was deduced from high-level ab initio calculations at the CCSD/TZ2P level on 2174 points. Parameters of the analytical potential energy functions were then fitted by these ab initio results. Three types of analytical functions: Simons-Parr-Finlan(SPF) polynomial, Jensen function and Sorbie-Murrell(SM) function. The equilibrium C-H bond length and H-C-H bond angle of CH2 are 1.075 Angstrom and 133.3 degree, respectively, with an energy of -39.0828910 hartree. CH2 correlates with the ground states of C+H2 and CH+H. The dissociation energies are 3.43eV for the first channel and 4.74eV for the second channel. The reference state is the ground states of three seperate atoms, C+2H, which is -37.7977887 hartree. The nonlinear-least-squares fitting of the parameters of the lobal potential functions was implemented by a modifiedvenberg-Marquardt algorithm with a finite- difference Jacobian.t-mean-square(RMS) error is 3.79 kcal/mol for SPF polynomial,kcal/mol for Jensen function and 4.29 kcal/ mol for SM function. The fits of SPF polynomial and Jensen function areccurate in the vicinity of ground state while SM function givesgood description at the dissociation regions of CH+H and C+H+H. According to 3-D graphs with fixed C-H bond length, SPF polyno- mial reports a wrong profile when the H-C-H bond angle is small and so does Jensen function.