Quantum Chemical Description of the Vibration Motion of Chrysene, Comparison Results of the MINDO/3-FORCES Method , ab initio and Density Functional (B3LYP)


Abstract Vibration frequencies and IR absorption intensities for the chrysene molecule in its calculated equilibrium structure were calculated quantum mechanically applying both the semiempirical MINDO/3-FORCES, the ab initio and density functional (B3LYP 6-311G) methods. The MINDO/3-FORCES frequency values were scaled applying scaling factors that had been evaluated formerly for naphthalene, anthracene and pyrene. Similarly the ab initio frequencies were scaled, and both treatments gave vibration motions of correct symmetries and sequence in frequency values. The calculated frequencies of MINDO/3-FORCES and scaled and ab initio methods, were close to the literature experimental frequencies. The (B3LYP 6-311G) treatment yielded frequency values that were very close to the experimental and MINDO/3-FORCES forces frequencies. Comparison of the results for different vibration modes showed a dependence of the vibration frequencies on the atomic site of the vibration. Thus the following relations were detected:sym(CH str.) (↑↑ ↓↓) > asym(CH str.) (↑↑ ↑↑) > asym(CH str.)(↑↓ ↓↑) > sym(CH str.)(↑↓ ↑↓) > sym(CH str.) , (↑↑ ↓↓) > asym(CH str.) , (↑↑ ↑↑) > asym(CH str.) > sym(CH str.) > asym(CH str.) > sym(CH str.) > sym(CH str.) , (↑↓ ↑↓) > asym(CH str.) , (↑↓ ↓↑) Generally the following relations hold;  (CH str.) >  (CH str.) and  (CH str.) >  (CH str.) , >  (CH str.) > (CH str.) Similar relations were detected for other valance vibrations.