Routines for calculation of analytical second derivatives for the effective core potential have been developed. The present version allows for spdf basis sets with spdfg projection operators for HF, DFT, and MP2 methods and has been incorporated into the Gaussian package. Analytical frequency analysis has been applied to the characterization of a critical structure of Cp2Ru2(μ-H)4 and to the study of the mechanism of reaction between Cu and CH2N2. Frequency analysis demonstrates that the structure previously found as the transition state of H2 dissociation of Cp2Ru2(μ-H)4 actually is a third-order stationary point. For various species of the system of Cu + CH2N2, DFT and MP2 second derivatives gave reasonable frequencies (∼5% average error) compared to the experimental in most cases, except that the N−N stretch was very poor at the MP2 level because of spin contamination in N2CuCH2. On the basis of vibrational frequencies, assignment has been made for adducts found experimentally between Cu and CH2N2. The...