ANALYTICAL 2ND DERIVATIVES FOR EFFECTIVE CORE POTENTIAL - APPLICATIONTO TRANSITION STRUCTURES OF CP(2)RU(2)(MU-H)(4) AND TO THE MECHANISM OF REACTION CU+CH(2)N(2)

Routines for calculation of analytical second derivatives for the effe ctive core potential have been developed. The present version allows f or spdf basis sets with spdfg projection operators for HF, DFT, and MP 2 methods and has been incorporated into the Gaussian package. Analyti cal frequency analysis has been applied to the characterization of a c ritical structure of Cp(2)Ru(2)(mu-H)(4) and to the study of the mecha nism of reaction between Cu and CH2N2. Frequency analysis demonstrates that the structure previously found as the transition state of H-2 di ssociation of Cp(2)Ru(2)(mu-H)(4) actually is a third-order stationary point. For various species of the system of Cu + CH2N2, DFT and MP2 s econd derivatives gave reasonable frequencies (similar to 5% average e rror) compared to the experimental in most cases, except that the N-N stretch was very poor at the MP2 level because of spin contamination i n N2CuCH2. On the basis of vibrational frequencies, assignment has bee n made for adducts found experimentally between Cu and CH2N2. The ener getics was also studied with the PCI-80 method and compared with DFT a nd ab initio results. The best estimated binding energy for Cu-CH2 is 60.8 kcal/mol. The end-on isomer is the only stable N-2 . CuCH2 specie s, and the side-on N-2 . CuCH2 isomerizes to the end-on form without b arrier. The best estimate of binding energy for N-2-CuCH2 is 19.4 kcal /mol for the end-on complex. The overall reaction for Cu + CH2N2 --> C uCH2 + N-2 is 34.9 kcal/mol exothermic. The reaction is found to take place without substantial barrier. The effect of recontraction of the ECP-associated basis set in DFT calculations is also briefly discussed .